toyota electrical and engine control systems manual

7/14/2019 Toyota Electrical and Engine Control Systems Manual

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GeneralElectricity is a form of energy called electricalenergy. It is sometimes called an "unseen" forcebecause the energy itself cannot be seen, heard,touched, or smelled.

However, the effects of electricity can be seen ...a lamp gives off light; a motor turns; a cigarettelighter gets red hot; a buzzer makes noise.

The effects of electricity can also be heard, felt,and smelled. A loud crack of lightning is easilyheard, while a fuse "blowing" may sound like a soft"pop" or "snap." With electricity flowing through

them, some insulated wires may feel "warm" andbare wires may produce a "tingling" or, worse,quite a "shock." And, of course, the odor of burnedwire insulation is easily smelled.

ELECTRICAL FUNDAMENTALS

© Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.



Electron TheoryElectron theory helps to explain electricity. Thebasic building block for matter, anything that hasmass and occupies space, is the atom. All matter -solid, liquid, or gas - is made up of molecules, or

atoms joined together. These atoms are thesmallest particles into which an element orsubstance can be divided without losing itsproperties. There are only about 100 differentatoms that make up everything in our world. Thefeatures that make one atom different from anotheralso determine its electrical properties.

ATOMIC STRUCTUREAn atom is like a tiny solar system. The center iscalled the nucleus, made up of tiny particles calledprotons and neutrons. The nucleus is surroundedby clouds of other tiny particles called electrons.

The electrons rotate about the nucleus in fixedpaths called shells or rings.

Hydrogen has the simplest atom with one proton inthe nucleus and one electron rotating around it.Copper is more complex with 29 electrons in fourdifferent rings rotating around a nucleus that has29 protons and 29 neutrons. Other elements havedifferent atomic structures.





ATOMS AND ELECTRICAL CHARGES

Each atomic particle has an electrical charge.Electrons have a negative (-) charge. Protonshave a positive charge. Neutrons have no charge;

they are neutral.

In a balanced atom, the number of electronsequals the number of protons. The balance of theopposing negative and positive charges holds theatom together. Like charges repel, unlike chargesattract. The positive protons hold the electrons inorbit. Centrifugal force prevents the electronsfrom moving inward. And, the neutrons cancel therepelling force between protons to hold the atom'score together.

POSITIVE AND NEGATIVE IONS

If an atom gains electrons, it becomes a negativeion. If an atom loses electrons, it becomes apositive ion. Positive ions attract electrons fromneighboring atoms to become balanced. Thiscauses electron flow.

ELECTRON FLOW

The number of electrons in the outer orbit(valence shell or ring) determines the atom'sability to conduct electricity. Electrons in the innerrings are closer to the core, strongly attracted tothe protons, and are called bound electrons.Electrons in the outer ring are further away fromthe core, less strongly attracted to the protons,

and are called free electron s .

Electrons can be freed by forces such as friction,heat, light, pressure, chemical action, or magneticaction. These freed electrons move away from theelectromot ive force, or EMF ("electron movingforce"), from one atom to the next. A stream of free electrons forms an electrical current.





CONDUCTORS, INSULATORS,SEMICONDUCTORS

The electrical properties of various materials aredetermined by the number of electrons in the outer

ring of their atoms.

• CONDUCTORS - Materials with 1 to 3 electrons inthe atom's outer ring make good conductors. Theelectrons are held loosely, there's room for more,and a low EMF will cause a flow of free electrons.

• INSULATORS - Materials with 5 to 8 electrons inthe atom's outer ring are insulators. The electronsare held tightly, the ring's fairly full, and a very highEMF is needed to cause any electron flow at all.Such materials include glass, rubber, and certainplastics.

• SEMICONDUCTORS - Materials with exactly 4electrons in the atom's outer ring are calledsemiconductors. They are neither goodconductors, nor good insulators. Such materialsinclude carbon, germanium, and silicon.

CURRENT FLOW THEORIES

Two theories describe current flow. Theconventional theory, commonly used forautomotive systems, says current flows from (+)to (-) ... excess electrons flow from an area of high potential to one of low potential (-). Theelectron theory, commonly used for electronics,says current flows from (-) to (+) ... excesselectrons cause an area of negative potential (-)and flow toward an area lacking electrons, an areaof positive potential (+), to balance the charges.

While the direction of current flow makes adifference in the operation of some devices, suchas diodes, the direction makes no difference to thethree measurable units of electricity: voltage,current, and resistance.





Terms Of Electric ity

Electricity cannot be weighed on a scale ormeasured into a container. But, certain electrical"actions" can be measured.

These actions or "terms" are used to describeelectricity; voltage, current, resistance, andpower .

VOLTAGE

Voltage is electrical pressure, a potential force or difference in electrical charge between twopoints. It can push electrical current through awire, but not through its insulation.

Voltage is pr essure

Current is flow.

Resistance opposes flow.

Power is the amount of work p erformed. Itdepends on the amount of pressure and thevolume of flow.

Voltage is measured in volts. One volt can push acertain amount of current, two volts twice asmuch, and so on. A voltmeter measures thedifference in electrical pressure between twopoints in volts. A voltmeter is used in parallel.





CURRENT

Current is electrical flow moving through a wire.Current flows in a wire pushed by voltage.

Current is measured in amperes, or amps, forshort. An ammeter measures current flow in amps.It is inserted into the path of current flow, or inseries, in a circuit.





RESISTANCE

Resistance opposes current flow. It is likeelectrical "friction." This resistance slows the flowof current. Every electrical component or circuit

has resistance. And, this resistance changeselectrical energy into another form of energy -heat, light, motion.

Resistance is measured in ohms. A special meter,called an ohmmeter , can measure the resistanceof a device in ohms when no current is flowing.





Factors Affecting ResistanceFive factors determine the resistance of conductors.

These factors are length of the conductor, diameter,temperature, physical condition and conductormaterial. The filament of a lamp, the windings of amotor or coil, and the bimetal elements in sensorsare conductors. So, these factors apply to circuitwiring as well as working devices or loads.

LENGTHElectrons in motion are constantly colliding asvoltage pushes them through a conductor. If twowires are the same material and diameter, the longerwire will have more resistance than the shorter wire.Wire resistance is often listed in ohms per foot (e.g.,spark plug cables at 5Ω per foot). Length must beconsidered when replacing wires.

DIAMETER

Large conductors allow more current flow with lessvoltage. If two wires are the same material andlength, the thinner wire will have more resistancethan the thicker wire. Wire resistance tables list ohmsper foot for wires of various thicknesses (e.g., size orgauge ... 1, 2, 3 are thicker with less resistance andmore current capacity; 18, 20, 22 are thinner withmore resistance and less current capacity).Replacement wires and splices must be the propersize for the circuit current.

TEMPERATUREIn most conductors, resistance increases as the wiretemperature increases. Electrons move faster, but notnecessarily in the right direction. Most insulators haveless resistance at higher temperatures.Semiconductor devices called thermistors have

negative temperature coefficients (NTC) resistancedecreases as temperature increases. Toyota's EFIcoolant temperature sensor has an NTC thermistor.Other devices use PTC thermistors.

PHYSICAL CONDITIONPartially cut or nicked wire will act like smaller wire withhigh resistance in the damaged area. A kink in thewire, poor splices, and loose or corroded connectionsalso increase resistance. Take care not to damagewires during testing or stripping insulation.

MATERIAL

Materials with many free electrons are goodconductors with low resistance to current flow.Materials with many bound electrons are poorconductors (insulators) with high resistance to currentflow. Copper, aluminum, gold, and silver have lowresistance; rubber, glass, paper, ceramics, plastics,and air have high resistance.





Voltage, Current, AndResistance In Circuits

A simple relationship exists between voltage,current, and resistance in electrical circuits.

Understanding this relationship is important forfast, accurate electrical problem diagnosis andrepair.

OHM'S LAW

Ohm's Law says: The current in a circuit is directlyproportional to the applied voltage and inverselyproportional to the amount of resistance.

This means that if the voltage goes up, the currentflow will go up, and vice versa. Also, as the

resistance goes up, the current goes down, andvice versa.

Ohm's Law can be put to good use in electricaltroubleshooting. But, calculating precise values for

voltage, current, and resistance is not alwayspractical ... nor, really needed. A more practical,less time-consuming use of Ohm's Law would beto simply apply the concepts involved:

SOURCE VOLTAGE is not affected by eithercurrent or resistance. It is either too low, normal, ortoo high. If it is too low, current will be low. If it isnormal, current will be high if resistance is low orcurrent will be low if resistance is high. If voltage istoo high, current will be high.

CURRENT is affected by either voltage orresistance. If the voltage is high or the resistanceis low, current will be high. If the voltage is low orthe resistance is high, current will be low.

RESISTANCE is not affected by either voltage or

current. It is either too low, okay, or too high. If resistance is too low, current will be high at anyvoltage. If resistance is too high, current will below if voltage is okay.





ELECTRIC POWER AND WORK

Voltage and current are not measurements of electric power and work. Power, in watts, is ameasure of electrical energy ... power (P) equals

current in amps (1) times voltage in volts (E),P = I x E. Work, in wattseconds or watt-hours, is ameasure of the energy used in a period of time ...work equals power in wafts (W) times time inseconds (s) or hours (h), W =P x time. Electricalenergy performs work when it is changed intothermal (heat) energy, radiant (light) energy, audio(sound) energy, mechanical (motive) energy, andchemical energy. It can be measured with a waft-hour meter.





Actions Of Current

Current flow has the following effects; motion,light or heat generation, chemical reaction, andelectromagnetism.

HEAT GENERATIONWhen current flows through a lamp filament,defroster grid, or cigarette lighter, heat isgenerated by changing electrical energy to thermalenergy. Fuses melt from the heat generated whentoo much current flows.

CHEMICAL REACTIONIn a simple battery, a chemical reaction betweentwo different metals and a mixture of acid andwater causes a potential energy, or voltage. Whenthe battery is connected to an external load,current will flow. The current will continue flowinguntil the two metals become similar and the mixturebecomes mostly water.

When current is sent into the battery by analternator or a battery charger, however, the

reaction is reversed. This is a chemical reactioncaused by current flow. The current causes anelectrochemical reaction that restores the metalsand the acid-water mixture.

ELECTROMAGNETISMElectricity and magnetism are closely related.Magnetism can be used to produce electricity. And,electricity can be used to produce magnetism.

All conductors carrying current create a magneticfield. The magnetic field strength is changed bychanging current ... stronger (more current),weaker (less current).

With a straight conductor, the magnetic fieldsurrounds it as a series of circular lines of force.With a looped (coil) conductor, the lines of force

can be concentrated to make a very strong field. The field strength can be increased by increasingthe current, the number of coil turns, or both. Astrong electromagnet can be made by placing aniron core inside a coil. Electromagnetism is used inmany ways.





Types Of Electrici ty

There are two types of electricity: static anddynamic. Dynamic electricity can be either directcurrent (DC) or alternating current (AC).

STATIC ELECTRICITYWhen two non conductors - such as a silk clothand glass rod - are rubbed together, someelectrons are freed. Both materials becomeelectrically charged. One is lacking electrons andis positively charged. The other has extraelectrons and is negatively charged. Thesecharges remain on the surface of the material anddo not move unless the two materials touch or areconnected by a conductor. Since there is noelectron flow, this is called static electricity.

DYNAMIC ELECTRICITYWhen electrons are freed from their atoms andflow in a material, this is called dynamic electricity.If the free electrons flow in one direction, theelectricity is called direct current (DC). This is the

type of current produced by the vehicle's battery. If the free electrons change direction from positive tonegative and back repeatedly with time, theelectricity is called alternating current (AC). This isthe type of current produced by the vehicle'salternator. It is changed to DC for powering thevehicle's electrical system and for charging thebattery.





ELECTRICAL FUNDAMENTALS ASSIGNMENT NAME:

1. Describe the atomic structure of an atom and name all it’s components.

2. Explain how an ION differs from an atom.

3. Explain the difference between “bound” and “free” electrons.

4 Explain the function of the “Valence ring”

5. Define the following items: Conductors, Insulators, and Semiconductors.

6. Describe the two theories of electron flow.

7. Define in detail “voltage” and how is it measured.

8. Define in detail “current” and how is it measured.

9. Define in detail “resistance” and how is it measured.

10. Explain the relationship between current and resistance.

11. List and describe the various factors that effect resistance.

12. Explain what ohms law is and how it can be used.

13. Describe the effects of “current flow” through a conductor.

14. Describe in detail the two general categories of “electricity”.

15. Describe the two types of “dynamic electricity”.



Electrical Circuits

A complete path, or circuit, is needed beforevoltage can cause a current flow throughresistances to perform work.

There are several types of circuits, but all requirethe same basic components. A power source(battery or alternator) produces voltage, or electrical potential. Conductors (wires, printedcircuit boards) provide a path for current flow.Working devices, or loads (lamps, motors),change the electrical energy into another form of energy to perform work. Control devices (switches, relays) turn the current flow on andoff. And, protection devices (fuses, circuitbreakers) interrupt the

current path if too much current flows. Too muchcurrent is called an overload, which coulddamage conductors and working devices.

A list of five things to look for in any circuit:

1. Source of Voltage

2. Protection Device

3. Load

4. Control

5. Ground

We will be identifying these items when we look at Automotive Circuits a little later in this book.

ELECTRICAL CIRCUITS

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Types Of Circuits

There are three basic types of circuits: series,

parallel, and series-parallel . The type of circuitis determined by how the power source,conductors, loads, and control or protectivedevices are connected.

SERIES CIRCUIT

A series circuit is the simplest circuit. Theconductors, control and protection devices, loads,and power source are connected with only onepath for current. The resistance of each devicecan be different. The same amount of current willflow through each. The voltage across each will

be different. If the path is broken, no currentflows.

PARALLEL CIRCUIT

A parallel circuit has more than one path for current flow. The same voltage is applied acrosseach branch. If the load resistance in each branchis the same, the current in each branch will be thesame. If the load resistance in each branch isdifferent, the current in each branch will bedifferent. If one branch is broken, current willcontinue flowing to the other branches.

SERIES-PARALLEL CIRCUIT

A series-parallel circuit has some components inseries and others in parallel. The power sourceand control or protection devices are usually inseries; the loads are usually in parallel. The samecurrent flows in the series portion, differentcurrents in the parallel portion. The same voltage isapplied to parallel devices, different voltages toseries devices. If the series portion is broken,current stops flowing in the entire circuit. If a

parallel branch is broken, current continuesflowing in the series portion and the remainingbranches.

ELECTRICAL CIRCUITS




SERIES CIRCUITS

In a series circuit, current has only one path. Allthe circuit components are connected so that thesame amount of current flows through each. The

circuit must have continuity. If a wire isdisconnected or broken, current stops flowing. If one load is open, none of the loads will work.

Use of Ohm's Law

Applying Ohm's Law to series circuits is easy.Simply add up the load resistances and divide thetotal resistance into the available voltage to find thecurrent. The voltage drops across the loadresistances are then found by multiplying thecurrent by each load resistance. For calculationexamples, see page 6 in the Ohms law section.

Voltage drop is the difference in voltage(pressure) on one side of a load compared to the

voltage on the other side of the load. The drop or loss in voltage is proportional to the amount of resistance. The higher the resistance, the higher the voltage drop.

When troubleshooting, then, you can see that moreresistance will reduce current and less resistancewill increase current. Low voltage would alsoreduce current and high voltage would increasecurrent. Reduced current will affect componentoperation (dim lamps, slow motors). But, increasedcurrent will also affect component operation (earlyfailure, blown fuses). And, of course, no current atall would mean that the entire circuit would notoperate. There are electrical faults that can causesuch problems and knowing the relationship

between voltage, current, and resistance will helpto identify the cause of the problem.

ELECTRICAL CIRCUITS




PARALLEL CIRCUITS

In a parallel circuit, current can flow through morethan one path from and to the power source. Thecircuit loads are connected in parallel legs, or

branches, across a power source. The pointswhere the current paths split and rejoin are called junctions. The separate current paths are calledbranch circuits or shunt circuits. Each branchoperates independent of the others. If one loadopens, the others continue operating.

Use of Ohm's Law

Applying Ohm's Law to parallel circuits is a bitmore difficult than with series circuits. The reasonis that the branch resistances must be combined tofind an equivalent resistance. Just remember that

the total resistance in a parallel circuit is less than

the smallest load resistance. This makes sensebecause current can flow through more than onepath. Also, remember that the voltage drop acrosseach branch will be the same because the sourcevoltage is applied to each branch. For examples of how to calculate parallel resistance, see page 6.

When troubleshooting a parallel circuit, the loss of one or more legs will reduce current because thenumber of paths is reduced. The addition of one or more legs will increase current because thenumber of paths is increased. Current can also bereduced by low source voltage or by resistance inthe path before the branches. And, current can beincreased by high source voltage or by one or more legs being bypassed. High resistance in one

leg would affect component operation only in thatleg.

ELECTRICAL CIRCUITS




SERIES-PARALLEL CIRCUITS

In a series-parallel circuit, current flows throughthe series portion of the circuit and then splits toflow through the parallel branches of the circuit.

Some components are wired in series, others inparallel. Most automotive circuits are series-parallel, and the same relationship betweenvoltage, current, and resistance exists.

Use of Ohm's Law

Applying Ohm's Law to series-parallel circuits is amatter of simply combining the rules seen for series circuits and parallel circuits. First, calculatethe equivalent resistance of the parallel loads andadd it to the resistances of the loads in series.

The total resistance is then divided into the sourcevoltage to find current. Voltage drop across seriesloads is current times resistance. Current inbranches is voltage divided by resistance. For calculation examples, see page 6.

When troubleshooting a series-parallel circuit,problems in the series portion can shut down theentire circuit while a problem in one leg of theparallel portion may or may not affect the entirecircuit, depending on the problem. Very highresistance in one leg would reduce total circuitcurrent, but increase current in other legs. Verylow resistance in one leg would increase totalcircuit current and possibly have the effect of bypassing other legs.

ELECTRICAL CIRCUITS




Ohm's Law

Fast, accurate electrical troubleshooting is easywhen you know how voltage, current, andresistance are related. Ohm's Law explains the

relationship:

• Current (amps) equals voltage (volts) divided byresistance (ohms) ... I = E ÷ R.

• Voltage (volts) equals current (amps) timesresistance (ohms) ... E = I X R.

• Resistance (ohms) equals voltage (volts) dividedby current (amps) ... R ÷ E = 1.

USING OHM'S LAW

The effects of different voltages and differentresistances on current flow can be seen in the

sample circuits. Current found by dividing voltageby resistance. This can be very helpful whendiagnosing electrical problems:

• When the resistance stays the same ... currentgoes up as voltage goes up, and current goesdown as voltage goes down. A discharged batteryhas low voltage which reduces current. Somedevices may fail to operate (slow motor speed). Anunregulated alternator may produce too muchvoltage which increases current. Some devicesmay fail early (burned-out lamps).

• When the voltage stays the same ... current goesup as resistance goes down, and current goesdown as resistance goes up. Bypassed devicesreduce resistance, causing high current. Looseconnections increase resistance, causing low

current.

ELECTRICAL CIRCUITS




SAMPLE CALCULATIONS

Here are some basic formulas you will find helpfulin solving more complex electrical problems. Theyprovide the knowledge required for confidence

and thorough understanding of basic electricity.

The following abbreviations are used in theformulas:

E = VOLTSI = AMPSR = OHMSP = WATTS

• Ohm's Law

Scientifically stated, it says: "The intensity Of the

current in amperes in any electrical circuit is equalto the difference in potential in volts across thecircuit divided by the resistance in ohms of thecircuit." Simply put it means that current is equal tovolts divided by ohms, or expressed as a formula,the law becomes:

I = E / R

or it can be written:

E = I X R

This is important because if you know any two of the quantities, the third may be found by applyingthe equation.

Ohm's law includes these two ideas:

1. In a circuit, if resistance is constant, currentvaries directly with voltage.

Now what this means is that if you take acomponent with a fixed resistance, say a light bulb,and double the voltage you double the currentflowing through it. Anyone who has hooked a six-volt bulb to a twelve-volt circuit has experiencedthis. But it wasn't "too many volts" that burned outthe bulb, it was too much current. More about thatlater.

2. In a circuit, if voltage is constant, current variesinversely with resistance.

This second idea states that when resistance goes

up, current goes down. That's why corrodedconnectors cause very dim lights - not enoughcurrent.

• Watts

A watt is an electrical measurement of power or work. It directly relates to horsepower. In fact, inthe Sl metric standards that most of the worlduses, engine power is given in watts or kilowatts.

Electrical power is easily calculated by the formula:

P = E X I

For instance, a halogen high-beam headlight israted or 5 amps of current. Figuring 12 volts in thesystem, we could write:

P = E X IP = 12 X 5P = 60 watts

ELECTRICAL CIRCUITS




RESISTANCE

The effect of individual resistors on the totalresistance of a circuit depends on whether thecircuit is series or parallel.

Series Circuits

In a series circuit, the total resistance is equal tothe sum of the individual resistors:

SERIES:

total R = R1 + R2 + R3 +

That is the basis of the concept of voltage drop.For example, if you had a circuit with three loads inseries (a bulb, resistor, and corroded ground) you

would add the three together to get totalresistance. And, of course, the voltage woulddrop across each load according to its value.

Parallel Circuits

Parallel circuits are a different story. In a parallelcircuit, there are three ways to find totalresistance. Method A works in all cases. Method Bworks only if there are two branches, equal or not. Method C works only if the branches are of equal resistance.

A. The total resistance is equal to one over thesum of the reciprocals of the individualresistors. That sounds confusing, but looking atthe formula will make it clearer:

PARALLEL:

n example will make it even clearer. Suppose thereis a circuit with three resistors in parallel: 4 ohms,2 ohms, and 1 ohm. The formula would look like

this:

That becomes:

Which becomes:

So there is a little more than one-half ohmresistance in the circuit. You can see that the moreresistors in parallel, the less the resistance.

In fact, the total resistance is always less than thesmallest resistor. This is why a fuse will blow if you add too many circuits to the fuse. There are somany paths for the current to follow that the totalresistance of the circuit is very low. That means

the current is very high - so high that the fuse canno longer handle the load.

B. For two resistors:

For a 3 ohm and a 5 ohm resistor that would be:

C. For several identical resistors, divide the valueof one resistor by the number of resistors, or:

Where R1 is the value of one resistor and n is thenumber of resistors. So if you had three 4 ohmresistors in parallel it would be:

ELECTRICAL CIRCUITS




ELECTRICAL CIRCUITS




ELECTRICAL CIRCUITS ASSIGNMENT NAME:

1. Draw and label the parts of a Series Circuit and a Parallel Circuit.

2. Explain the characteristics of “Voltage” and how it differs between a SeriesCircuit and a Parallel Circuit.

3. Explain the characteristics of “Current” and how it differs between a SeriesCircuit and a Parallel Circuit.

4. Explain the characteristics of “Resistance” and how it differs between a SeriesCircuit and a Parallel Circuit.



Power Sources On The Car

Two power sources are used on Toyota vehicles.When the engine is not running or is being started,the battery provides power. When the engine is

running, the alternator provides power for thevehicle's loads and for recharging the battery.

THE BATTERY

The battery is the primary "source" of electricalenergy on Toyota vehicles when the engine is notrunning or is being started. It uses anelectrochemical reaction to change chemicalenergy into electrical energy for starting, ignition,charging, lighting, and accessories.

All Toyota vehicles use a 12-volt battery. Batteries

have polarity markings ... the larger (thicker)

terminal is marked "plus" or "POS" (+), the other terminal is marked “minus" or "NEG" (-). Correctpolarity is important; components can be damaged

if the battery is connected backwards.

THE ALTERNATOR

The alternator is the heart of the vehicle's electricalsystem when the engine is running. It useselectromagnetism to change some of the engine'smechanical energy into electrical energy for powering the vehicle's loads and for charging thebattery.

All Toyota alternators are rated by amps of currentoutput ... from 40 to 80 amps.

ELECTRICAL COMPONENTS




Loads

Working devices - or loads - consume electricity.They change electrical energy into another form of energy to do work. This energy may be thermal

(heat), radiant (light), mechanical (motive), audio(sound), chemical, or magnetic. The electricalenergy is changed by the resistance of theworking device. Resistance is put to work in manyways on Toyota vehicles.

PERFORM WORK

Some components use resistance to reducecurrent flow and change electrical energy(voltage) into heat, light, or motion. Resistanceproduces heat in electric window defrosters andcigarette lighters. Resistance produces light in

lamp filaments. And, resistance produces motion inmotors and solenoid coils. All circuit loads useresistance to perform work.

CONTROL CURRENT

Other components and systems use resistance for current control. Ignition primary resistors, alsocalled ballast resistors, maintain and protect theelectronic control unit (ECU) from excessivecurrent. The headlamp rheostat adds or subtractsresistance to dim or brighten interior lamps. A

carbon pile resistance in the Sun VAT-40 tester "loads" the battery for cranking-voltage andcharging system tests. A sliding contactresistance is used on some A/C and heatingcontrols to adjust interior temperature byincreasing or decreasing air volume and fanspeed. A wire-wound resistor is used on somefuel pumps to reduce pump speed.

REDUCE ARCING AND "RFI"

Some ignition components use resistance toreduce arcing and radio frequency interference

(RFI). Condensers use the high resistance of adielectric (insulating) material to separateconductive plates that soak up electrostaticcharges and current surges that cause RFI andpoint arcing. Spark plug cables, also called carbonresistance wires, reduce current flow buttransmit high voltage to the spark plugs. Thiscauses an extremely hot spark without RFI or rapidburning of the plug electrodes. Spark plugs,themselves, have a carbon core to achieve thesame results.

SENSE OPERATING CONDITIONS

Other components use resistance in sensing andmonitoring operating conditions. The resistance

added to or subtracted from a sensing circuitchanges the current flow which is used for inputto a control device, gauge, or actuator. The coolanttemperature sensor uses a device that changesresistance with temperature. The fuel-level sensor uses a type of potentiometer, or sliding-contactresistance. The automatic headlamp control uses aphotoresistor. The manifold vacuum sensor uses acrystal which changes resistance with pressure.

And, with the use of electronic control systemsgrowing rapidly, many more sensors and actuatorsare using the variation of resistance to operate.





Types Of Resistors

Three basic types of resistors are use a mautomotive electrical systems ... fixed value,stepped or tapped, and variable. Different symbols

are used for the different types of resistors.

FIXED-VALUE RESISTORS

Two types of fixed-value resistors are used: wire-wound and carbon.

Wire-wound resistors are made with coils of resistance wire. Sometimes called power

resistors, they are very accurate and heat stable.The resistance value is marked.

Carbon resistors are common in Toyotaelectronic systems. Carbon is mixed with binder;the more carbon, the lower the resistance. Somehave the resistance value stamped on, others arerated by wafts of power; most have color-codebands to show the resistance value. Four bandsare used ... the first two bands give the resistancedigits, the next band is the number of zeros, andthe last band gives the "tolerance."

A resistor with four bands - red, green, black, andbrown from left to right - would be sized asfollows:

• The first two bands set the digits ... red (2), green

(5).

• The next band is the number of zeros. Black is "0"zeros. So the resistor has a base value of 25Ω.

• And, the last band is the tolerance ... brown (1%). So, the resistance value is "25 ohms plus or minus .25 ohms" (24.75Ω to 25.25Ω ).





STEPPED OR TAPPED RESISTORSStepped or tapped resistors have two or morefixed resistance values. The different resistances(carbon or wire) are connected to differentterminals in a switch. As the switch is moved,

different resistance values are placed in thecircuit. A typical Toyota application is in the heater motor's blower-fan switch.

VARIABLE RESISTORSThree types of variable resistors are used:rheostats, potentiometers, and thermistors.• RHEOSTAT - Toyota uses a rheostat on the

headlamp switch to dim or brighten dash panellighting. Rheostats have two connections ... oneto the fixed end of a resistor, one to a slidingcontact on the resistor. Turning the controlmoves the sliding contact away from or toward

the fixed end, increasing or decreasing theresistance.

• POTENTIOMETER - Toyota uses a potentiometer in the EFI airflow meter. Potentiometers havethree connections ... one at each end of aresistor and one on a sliding contact. Turning thecontrol places more or less resistance in thecircuit.

• THERMISTOR - Toyota uses NTC (negativetemperature coefficient) thermistors intemperature sensors and PTC (positivetemperature coefficient) thermistors in theelectric assist choke. Both types of thermistorschange resistance with increasing temperature(NTC, resistance goes down as temperaturegoes up; PTC, resistance goes up as temperaturego up.)





Controls

Control devices used in electrical circuits onToyota vehicles include a variety of switches,relays, and solenoids. Electronic control devices

include capacitors, diodes, and transistors.Controls are needed to start, stop, or redirectcurrent flow. Most switches require physicalmovement for operation, relays and solenoids areoperated with electromagnetism, electroniccontrols are operated electrically.

SWITCHES

Switches are the most common circuit controldevice. They usually have two or more sets of contacts. Opening the contacts is called "opening"or "breaking the circuit," while closing the contacts

is called "closing" or "making" the circuit. "Poles"refer to the number of input circuit terminals."Throws" refer to the number of output circuits.Such switches are referred to as SPST (single-pole, single-throw), SPDT (single-pole, double-throw), and MPMT (multiple-pole, multiple-throw).

The various types of switches include:

• Hinged pawl - a simple SPST switch to make or break a circuit.

• Momentary contact - another SPST switch,

normally open or closed, which makes or breaksthe circuit when pressed ... typically used for thehorn switch.

• SPDT - one wire in, two wires out ... commonlyused in high-beam / low-beam headlamp circuits.

• MPMT - movable contacts are linked to sets of output terminals ... may be used for thetransmission neutral start switch.

• Mercury switch - liquid mercury flows betweencontacts to make circuit ... commonly used to turnengine compartment and trunk lamps on and off.

• Temperature-sensitive switch - a bimetalelement bends when heated to make contactcompleting a circuit or to break contact opening acircuit. The same principle is also used in time-delay switches and flashers.





RELAYS A relay is simply a remote-control switch, whichuses a small amount of current to control a largeamount of current. A typical relay has a controlcircuit and a power circuit. The control circuit is

fed current by the power source, and the currentflows through a switch and an electromagneticcoil to ground. The power circuit is also fedcurrent from the power source, and the currentflows to an armature which can be attracted bythe magnetic force on the coil.

In operation, when the control circuit switch isopen, no current flows to the relay. The coil is notenergized, the contacts are open, and no power goes to the load. When the control circuit switch isclosed, however, current flows to the relay andenergizes the coil. The resulting magnetic field

pulls the armature down, closing the contacts andallowing power to the load.

Many relays are used on Toyotas for controllinghigh current in one circuit with low current inanother circuit. The relay control circuit can beswitched from the power supply side or, morecommon in Toyotas, from the ground side.

SOLENOIDSSolenoids are electromagnetic switches with amovable core that converts current flow intomechanical movement.

In a "pulling" type solenoid, the magnetic field pullsa core into a coil. These solenoids are calledmagnetic switches on Toyota starters. A pull-in coil"pulls" the core into the coil, and a hold-in coil"holds" the core in place.

In a "push-pull" type solenoid, a permanent magnet

is used for the core. By changing the direction of current flow, the core is "pulled in" or "pushed out."

A typical use is on electric door locks.





CAPACITORS

Capacitors use an electrostatic field to "soak up" or store an electrical charge. In a circuit, a capacitor will build up a charge on its negative plate. Current

flows until the capacitor charge is the same as thatof the power source. It will hold this charge until itis discharged through another circuit (such asground). Always handle capacitors with care;once charged, they can be quite shocking longafter the power is removed.

• TYPES

A capacitor has two conducting plates separatedby an insulating material or dielectric. Three typesare used: ceramic for electronic circuits, paper and foil for noise suppression in charging and

ignition systems, and electrolytic for turn-signalflashers. Different symbols are used for ordinaryand electrolytic capacitors.

• RATINGS

Automotive capacitors are rated in microfarads,and the rating is usually stamped on the case.

Always choose a capacitor rated for the maximumexpected voltage.

• DIAGNOSIS / TESTING

Capacitors can be tested for short circuits using anohmmeter. Connect one test lead to the capacitor mounting clip and the other test lead to thecapacitor pigtail connector. The meter needle willfirst show some continuity as the meter's batterycharges the capacitor, then will swing to infiniteresistance (∞). If only continuity is seen, thecapacitor is most likely shorted.





Electronics"Electronic" devices and systems provide today'svehicles with added comfort, convenience, safety,and performance.

These devices and systems, like their "electrical"counterparts, control electricity to do work. Thecurrent flows through a semiconductor - rather than through wires. The movement usuallyproduces an electrical signal - rather than heat,light, or motion. And, this signal may be transmitted,amplified, or used in special circuits to performlogical decision-making functions.

Since there are seldom any moving(electromechanical) parts, these devices andsystems are often called solid-state electronics.

SEMICONDUCTORSSemiconductors can act like conductors or insulators. They have a resistance higher than thatof conductors like copper or iron, but lower thanthat of insulators like glass or rubber. They havespecial electrical properties:• Conductivity can be increased by mixing incertain substances;

• Resistance can be changed by light, temperature,or mechanical pressure; and,

• Light can be produced by passing currentthrough them.

DIODESDiodes are semiconductor devices which act asone way electrical check valves. Diodes will allowcurrent flow in one direction (anode to cathode),but block it in the reverse direction (cathode to

anode).

• TYPES / USESThere are several types of diodes. Rectifyingdiodes change low-current AC to DC in thecharging system. Power rectifiers can handlelarger currents in electronic power supplies.Zener diodes can function as voltage sensitiveswitches. They turn "on" to allow current flowonce a certain voltage is reached. They are oftenused in voltage regulation applications. Light-emitting diodes (LEDs) are used for indicator lights and digital displays. And, photodiodes detect

light for sensors.

• SYMBOLSSymbols for various diodes are shown. The arrowpoints in the "forward" direction of current flow(anode to cathode). Zener diodes have a "Z"shaped bar on the cathode side. LEDs andphotodiodes are enclosed in a circle with incomingor outgoing light indicated.





TransistorsTransistors are semiconductor devices for controlling current flow. A "transistor"(transformer + resistor) transfers signals acrossthe resistance of two semiconductor materials.

• TYPES / USESThere are many types of transistors. Ordinary or bipolar transistors are most common for switchingand amplifying. Power transistors are avariation for larger currents; exposed metal carriesaway heat. Phototransistors are another variation, used as light-sensitive switches inspeedometer and headlamp systems.

Field-effect transistors (FETs) are quitedifferent. They are used as switches, amplifiers,and voltage controlled resistors.

• SYMBOLSBipolar transistors are shown with a line andarrow for the emitter , a heavy T-shaped line for the base, and a line without an arrow for thecollector . The emitter arrow points to the circuit'snegative side. Phototransistors have incoming lightarrows added. And, FETs have an arrow showingnegative (N) or positive (P) voltage.

• OPERATIONIn bipolar transistors, a small base current (I b)

between the emitter-base "turns on" the transistor and causes a larger current (I c) to flow betweenthe emitter-collector. In phototransistors, lightstriking the base "turns on" the transistor. Thisswitches on a second transistor which amplifiesthe signal.

ELECTRONIC CIRCUITS AND SYSTEMSIndividual semiconductor devices are calleddiscrete devices, a number of them may be usedin a circuit. Such devices are common in charging,ignition, and headlamp circuits that handle large

amounts of power.

The more sophisticated electronic control systemsnow being used on the vehicle, however, makeuse of integrated circuits andmicroprocessors or onboard computers.

• INTEGRATED CIRCUITS An integrated circuit (IC) has hundreds, eventhousands, of discrete devices on a single siliconchip. These include diodes, transistors, resistors,and capacitors. The IC is usually packaged inceramic or plastic and each tiny device inside is

connected to one or more leads that plug into alarger on-vehicle circuit. One type can processanalog signals - those that change continuouslywith time. Another type can process digitalsignals - those that change intermittently "on" or "off" with time.

• MICROPROCESSORSMicroprocessors, or on-board computers, are usedon various electronic control systems. Suchsystems have three basic parts: 1) sensors tellwhat is happening; 2) the microprocessor computes the data and decides what to do; and 3)the actuators or controls respond to change or display the condition. The ECS and ABS areexamples of such systems.





Protective Devices

Electrical circuits are protected from too muchcurrent by fuses, fusible links, and circuitbreakers. Such devices will interrupt a circuit to

prevent high current from melting conductors anddamaging loads. Each of these circuit protectiondevices is sensitive to current, not voltage, and israted by current-carrying capacity. They areusually located at, or near, the power source for the circuit being protected. As such, they areusually a good starting point during electricalproblem troubleshooting. Remember, though, thesedevices "blow" or open a circuit because of aproblem. Always locate and correct the problembefore replacing a fuse or fusible link or resettinga circuit breaker.

FUSES

Fuses are the most common circuit protectiondevice. Fuses have a fusible element, or low-

melting-point metal strip, in a glass tube or plug-inplastic cartridge. These fuses are located in a fuseblock under the dash or behind a kick panel. Mostcircuits - other than the headlamp, starter, andignition systems - receive power through the fuseblock. Battery voltage is supplied to a buss bar inthe block. One end of each fuse is connected tothis bar, the other end to the circuit it protects.

Fuse ratings range from 0.5 to 35 amps, but 7.5 -amp to 20-amp fuses are most common.





FUSIBLE LINKS

Some circuits use fusible links, or fuse links, for overload protection. Toyotas can have as many assix fusible links protecting circuits for charging,

starting, ignition, and certain accessories. Checkthe "Power Source" page in the Electrical WiringDiagram manual for the specific vehicle.

A fusible link is a short length of smaller gaugewire installed in a circuit with larger conductors.High current will melt the link before it melts thecircuit wiring. Such fuse links have specialinsulation that blisters or bubbles when the linkmelts. A melted link must be replaced with one of the same size after the cause of the overload hasbeen identified and the problem corrected.

CIRCUIT BREAKERS

Circuit breakers are used for protecting circuitstemporary overloads may occur and where power must be quickly restored. A bimetal strip is used,

similar to that in a temperature-sensitive switch.When heated, the two metals expand differentlyand cause the strip to bend. The "breaker" isnormally closed and it opens when the bimetalelement bends. Some circuit breakers are self-resetting, others must be manually reset.

Circuit breakers are used on Toyota vehicles toprotect circuits for the defogger, heater, air conditioner, power windows, power door locks,and sun roof.





ELECTRICAL COMPONENTS ASSIGNMENT NAME:

1. Describe two power sources used in a vehicle.2. Explain the term “load” and how it is used in a circuit.

3. Describe the two types of resistors and how each is used.

4. Explain the color code of a resistor that is: “Brown, Orange, Red, Silver.

5. Describe a “stepped resistor “ and how it differs from a “fixed resister”.

6. List and describe three types of “variable resistors”.

7. Explain how a “NTC” thermistor differs from a “PTC” thermistor.

8. List six types of switches used in automobiles.

9. Describe the two circuits used in a relay.

10 Explain how a “relay” differs from a “solenoid”.

11. Explain how current flows into a “capacitor”.

12. Explain the term “semiconductor”.

13. Draw, label, and describe the basic function of a “diode”.

14. Draw, label, and describe the basic function of a “bi-polar transistor”.

15. Explain the term “Integrated Circuit”.

16. List three types of “circuit protective devices”.

17. Describe the basic construction of a “fuse” or “fuse element”.

18. Explain how a “fuse element” differs from a “fusible link”.

19. Describe the basic construction of a “circuit breaker”.



ANALOG VS. DIGITAL METERS

U lt ima tely, your dia gnosis of vehicle

electrical system problems will comedown t o using a voltmeter , a mmeter , orohmmeter t o pinpoint th e exa ct locat ion ofth e problem. There a re tw o ty pes of eachmeter—a na log and dig i t a l .

Ana log meters use a n eedle andcalibr ate d scale to ind icate values.

Digital m eters d isplay th ose values on adigital display.

This chapt er w ill help you und ersta nd

how th ese meters work as w ell a s theadva nta ges and disadva nta ges of ea ch.

B efore using a meter , rea d themanufac turer ' s opera t ing inst ruct ions .Reading a na log meters usua l ly requiressimple mental calculat ions. For example,a meter might ha ve three vol tage ra nges :4.0 V, 20 V a nd 40 V, but only t w o sca les:4.0 V an d 20 V. In order t o use th e 40 Vra nge, you need to multiply t he needlereading on the 4.0 V scale by 10 (or for

th a t m a tt er, the 20 V sca le by 2).

Digita l meters a re usually simpler toread a nd ma ny w ill a djust to the properra nge requir ed for th e circuit or devicethey are

conn ected t o. These meters a re known a sa uto-ra nging meters . Other dig i t a lmeters require t he operat or t o select t heproper ra nge . In a ny case i t is impor ta ntto lea rn t he symbols used in a digita lreadout so you can int erpret th e reading.The electrica l unit s of measu re sym bolsa re :

M for m ega or mil lionK for k ilo or th ousan dm for mil li or on e-th ousan dthu for m icro or on e-millionth

The three types of meters—voltmeters,a mmeters a nd ohmmeters—connect toth e circuits or devices in different w a ys.This is n ecessary to get a ccura temeasurements a nd to prevent da ma ge toth e meters.

VOLTMETERS—

ANALOG AND DIGITAL

Voltmeters m easure voltage or volta ge

drop in a circuit . Volta ge drop can beused t o locat e excessive resista nce in th ecircuit w hich could cause poorperforma nce or improper opera t ion. La ckof volta ge at a given point ma y indica te a nopen circuit or gr ound. On t he otherha nd, low volta ge or high volta ge drop,ma y indica te a high resis ta nce problemlike a poor conn ect ion.

Voltm eters must be connected in par a llelw ith t he device or circuit so tha t t hemeter can t ap off a smal l a mount o fcurrent. Tha t is, t he positive or red lead isconn ected t o th e circuit closest t o thepositive side of th e bat tery . The nega tiveor black lead is connected t o ground or th enega tive side of th e circuit . I f a voltm eteris connected in series, its high r esista ncew ould reduce circuit current a nd cau se afa lse reading .

ANA LOG AND DIGITAL METERS

Pa ge 1 © Toyota Motor S ales, U .S.A., Inc. All Rights R eserved.



B eca use voltmeters ar e alw ay s hooked t oa circuit in par a llel, they become par t ofth e circuit a nd reduce th e total resista nceof th e circuit . I f a voltmeter ha s aresistan ce tha t is t oo low in compar ison t oth e circuit , it will give a fa lsemea surement . The false read ing is due toth e meter cha nging t he circuit bylow er ing th e resis tan ce , which increa ses

th e curren t flow in t he circuit . The effecta voltmeter ha s on th e circuit t o which i t

is a t t a ched is sometimes referred to a s" loadin g effect" of th e meter. The loa dingeffect a voltmet er ha s on a circuit isdetermined by the tota l resista nce of thecircuit in rela tion to th e impeda nce of th evoltmeter.

Every voltmeter ha s an impeda nce,w hich is t he meter 's interna l resis ta nce.The impedan ce of a conventiona l a na logvoltmet er is expressed in " ohms per volt . "The am ount of resista nce a n a na logvoltm eter represents t o the circuitchan ges in relat ion to the scale on w hichit is placed. Digita l voltmeters, on theother ha nd, ha ve a f ixed impedancew hich does not cha nge from scale to sca lea nd is usu a lly 10 M ohms or more.

Impeda nce is th e biggest dif ferencebetw een a na log an d digita l voltmeters.Since most d igita l voltmeters ha ve 50t imes more impedance tha n a na logvoltmeters, digita l meters ar e morea ccura te wh en measur ing vol ta ge inhigh resis ta nce circui t s .

For example, i f you are using a low impeda nce (20,000 ohm s per volt) a na logmeter on th e 20 volt scale (th e voltm eterrepresent s 400,000 ohms resist a nce to thecircuit) to measur e volta ge drop a cross a1,000,000 ohm component in a circuit , tw o

an d a ha l f t imes a s m uch cur rent i sf lowing t hrough the meter tha n th roughth e component . You a re no longermeasu ring just th a t component , but th ecomponent plus y our meter, givin g you afalse reading of the a ctua l volta ge dropacross the component. This situationmight lead you to believe the volta ge at thecomponent is low or t ha t t here is highresista nce somew here in th e circuit orth a t t he component is defective w hen it isjust t he meter you are using.

If you use a digita l meter wit h 10 millionohms of impeda nce to test t he sam ecomponent , only 1/10 of t he curr ent w illf low through th e meter , wh ich mea ns i tha s very lit t le effect on th e circuit beingm e a s u r e d .





AMMETERS—

ANALOG AND DIGITAL

Ammeters m easure a mpera ge , orcurrent f low, in a circuit , an d provideinforma t ion on current dra w a s wel l a scircuit cont inuity . High current f low indica tes a shor t c ircui t , unintent iona lground or a defective component. S omety pe of defect h a s lowered t he circuitresis ta nce. Low current f low ma yindicate h igh resista nce or a poorconnect ion in th e circuit or a dischar gedbat tery. No current indicat es an opencircuit or loss of pow er.

Ammeters m ust a lwa ys be connected inseries w ith t he circuit , never in para llel .Tha t is , a l l the circuit current m ust f low th rough th e meter. I t is conn ected bya tt a ching t he positive lead t o the positiveor ba tt ery side of th e circuit , a nd t henega tive lead t o nega tive or ground side of

the c ircui t , a s shown.CAUT ION : Th ese m eters hav e extrem ely low

interna l resistance. If conn ected in parallel, the

current ru nn ing through th e parallel branch

created by the m eter m ight be high enough to

dam age the m eter along with th e circuit the m eter

is connected to. Also, since all the current will

fl ow throu gh the a m m eter when it is con nected be

sure tha t th e circuit current will n ot exceed th e

m aximu m rat ing of the m eter.

There is not a grea t difference betw eena na log and dig it a l am meters . Dig i t a lmeters a re often capa ble of measur ingsma l ler currents , a l l the wa y down tomicroa mps. They a re easier t o usebeca use th ey give a specific va lue,eliminat ing th e need t o interpret t hea na log meter 's needle on i t s scale .G enera l ly speaking , most dig i t a la mmeters a re combined wit h a voltmeter .

OHMMETERS—

ANALOG AND DIGITAL

An ohmmeter is powered by a n int erna l

bat t ery tha t a pplies a sma ll voltage to acircuit or component a nd m eas ures how much current f lows t hrough t he c ircuitor component . I t then displa ys t he resulta s resista nce. Ohmm eters ar e used for

checking cont inui t y a nd for mea sur ingth e resista nce of components . Zeroresista nce indica tes a sh ort w hile infinite

resista nce indicat es an open in a circuitor device. A read ing higher th a n t hespecification indicates a faulty componentor a high r esista nce problem such a sburnt cont a cts, corroded termina ls orloose connections.





Ohmmeters, beca use they a re self-pow ered, must never be conn ected t o apow ered circuit a s th is ma y blow a fuse inthe meter a nd da mage i t s ba t t ery . Un lessth e circuit being mea sured cont a ins adiode, polarity (a t t aching t he leads in apar t icular order) is inconsequent ial .

An a na log ohmmeter should beca libra ted regularly by connect ing t he tw olea ds together a nd zeroing the meter withth e ad just knob. This compensa tes forcha nges in the sta te of cha rge of theinternal bat tery.

CAUT ION : Analog ohm m eters may apply ahigher voltage to a circuit t han a d igital

ohm m eter, causin g dam age to solid state

components .

Use analog ohm m eters with care. Digital m eters,

on th e other h an d, ap ply less voltage to a circuit , so

dam age is less l ikely.

Ana log meters can a lso bias, or turn on,semi-condu ctors a nd cha nge th e circuitby a llow ing current t o flow to oth erport ions of the circuit .

Most digita l meters ha ve a low volta geset t ing w hich will not bia s semi-conductors an d a higher volta ge set t ingfor test ing semiconductors. Theinforma tion displayed on a d igita l meterin t he diode test function differs from onemeter brand t o a nother . Some digita lmeters wi l l displa y a va lue wh ichrepresents t he perceived resista nceof th e diode in forw a rd bia s. Other metersw ill display the forw a rd bias voltage drop

of the diode.

Digita l ohmm eters do ha ve onelimitat ion. Due to the small a mount ofcurrent t hey pass t hrough th e devicebeing tested, t hey can not check somesemicond uctors in circuits , such a s aclam ping diode on a r elay coil.

Man y a na log ohmmeters w i l l , wh ensw itched t o the ohm funct ion, reverse thepolarity of the t est leads. In other w ords,the red lea d ma y become negat ive and thebla ck lea d ma y become positive. Themeter w ill funct ion properly a s long a syou are aw a re of this a nd reverse theleads. This is especially importa nt w henw orking wi th diodes or t ra nsis tors whicha re polarity sensit ive an d only a llow current t o flow from th e positive to thenega tiv e end. To check for polar ityreversal , set th e ohmm eter in ohmfunct ion an d connect i t s leads t o the lea dsof a v oltm eter (red t o red, black to bla ck).

I f th e voltmeter shows a negat ive value,tha t pa r t icular ohmmeter reversespolarit y in ohm funct ion. Most digita lmeters do not reverse pola rity .

You should note tha t ohmmeters d o li t t legood in low resista nce, high current -ca rrying circui t s such a s s t a r ters . Theycann ot f ind points of high resista ncebeca use they only use a sma ll amount of

current f rom their interna l ba t ter ies . In ala rge conductor (such as a ba tt ery cable),th is current meets l i t t le resista nce. Avolta ge drop test durin g circuit opera tionis much more effective a t loca tin g point sof high r esista nce in t his t ype of circuit .

Ta ken w ith permission from theToyota Advanced Electrical Course#672,





ANALOG AND DIGITAL METERS

ASSIGNMENT NAME:

1. Expla in how read ing an Ana log meter d if fer s from a Digi t a l meter.

2. Expla in the fol lowing elect r ica l uni t s of measure symbols ( M, K, m, u ).

3. List th ree t ypes of met er s.

4. Descr ibe how voltmeters a re connected to a cir cu it .

5. E x pla i n how “ m et er loa d ing” a ff ect s t he cir cu it .

6. Descr ibe “meter impedance” and how i t ef fect s a ci rcu it ?

7. L is t the f ixed impedance va lue of a d ig it a l vol tmeter.

8. Expla in how the impedance of a d igi t a l meter d if fer s from an a na log meter .

9. D es cr ibe how a m m et er s a r e connect ed t o a cir cu it .

10. Expla in how ana log ohmmeters dif fer f rom dig it a l ohmmeters in setup.

11. Expla in what precaut ions one should t a ke whi le connect ing an ohmmeter to acircuit.



CONDUCTORS

Conductors are needed to complete the path for electrical current to flow from the power source to the

working devices and back to the power source.

POWER OR INSULATED CONDUCTORS

Conductors for the power or insulated current pathmay be solid wire, stranded wire, or printed circuitboards. Solid, thin wire can be used when current islow. Stranded, thick wire is used when current is high.Printed circuitry - copper conductors printed on aninsulating material with connectors in place - is usedwhere space is limited, such as behind instrumentpanels.

Special wiring is needed for battery cables and for ignition cables. Battery cables are usually very thick,stranded wires with thick insulation. Ignition cablesusually have a conductive carbon core to reduce

radio interference.

GROUND PATHS

Wiring is only half the circuit in Toyota electricalsystems. This is called the "power" or insulated sideof the circuit. The other half of the path for currentflow is the vehicle's engine, frame, and body. This iscalled the ground side of the circuit. These systemsare called single-wire or ground-return systems.

A thick, insulated cable connects the battery'spositive ( + ) terminal to the vehicle loads. Asinsulated cable connects the battery's negative ( - )

cable to the engine or frame. An additional groundingcable may be connected between the engine andbody or frame.

Resistance in the insulated side of each circuit willvary depending on the length of wiring and thenumber and types of loads. Resistance on theground side of all circuits must be virtually zero. This isespecially important: Ground connections must besecure to complete the circuit. Loose or corrodedground connections will add too much resistance for proper circuit operation.

SYSTEM POLARITY

System polarity refers to the connections of thepositive and negative terminals of the battery to theinsulated and ground sides of the electrical system.On Toyota vehicles, the positive (+) battery terminal isconnected to the insulated side of the system. This iscalled a negative ground system having positivepolarity.

Knowing the polarity is extremely important for proper service. Reversed polarity may damage alternator diodes, cause improper operation of the ignition coiland spark plugs, and may damage other devicessuch as electronic control units, test meters, and

instrument panel gauges.

WIRE, TERMINAL AND CONNECTOR REPA IR




HARNESSES

Harnesses are bundles of wires that are groupedtogether in plastic tubing, wrapped with tape, or

molded into a flat strip. The colored insulation of various wires allows circuit tracing. While theharnesses organize and protect wires going tocommon circuits, don't over look the possibility of aproblem inside.

WIRE INSULATION

Conductors must be insulated with a covering or "jacket." This insulation prevents physical damage,and, more important, keeps the current flow in thewire. Various types of insulation are used dependingon the type of conductor. Rubber, plastic, paper,ceramics, and glass are good insulators.

CONNECTORS

Various types of connectors, terminals, and junctionblocks are used on Toyota vehicles. The wiringdiagrams identify each type used in a circuit.Connectors make excellent test points because thecircuit can be "opened" without need for wire repairsafter testing. However, never assume a connection is

good simply because the terminals seem connected.Many electrical problems can be traced to loose,corroded, or improper connections. These problemsinclude a missing or bent connector pin.





CONNECTOR REPAIR

The repair parts now in supply are limited to thoseconnectors having common shapes and terminal

cavity numbers. Therefore, when there is no availablereplacement connector of the same shape or terminalcavity number, please use one of the alternativemethods described below. Make sure that theterminals are placed in the original order in theconnector cavities, if possible, to aid in futurediagnosis.

1 . When a connector with a different number of terminals than the original part is used, select aconnector having more terminal cavities thanrequired, and replace both the male and femaleconnector parts.

Example: You need a connector with sixterminals, but the only replacement available is aconnector with eight terminal cavities. Replaceboth the male and female connector parts withthe eight terminal part, transfering the terminalsfrom the old connectors to the new connector.

2. When several different type terminals are used inone connector, select an appropriate male andfemale connector part for each terminal typeused, and replace both male and femaleconnector parts.

Example: You need to replace a connector thathas two different types of terminals in oneconnector. Replace the original connector withtwo new connectors, one connector for one typeof terminal, another connector for the other typeof terminal.

3. When a different shape of connector is used, firstselect from available parts a connector with theappropriate number of terminal cavities, and onethat uses terminals of the same size as, or larger

than, the terminal size in the vehicle. The wirelead on the replacement terminal must also be thesame size as, or larger than, the nominal size of the wire in the vehicle. ("Nominal" size may befound by looking at the illustrations in the back of this book or by direct measurement across thediameter of the insulation). Replace all existingterminals with the new terminals, then insert theterminals into the new connector.

Example: You need to replace a connector that isround and has six terminal cavities. The onlyround replacement connector has three terminalcavities. You would select a replacement

connector that has six or more terminal cavitiesand is not round, then select terminals that will fitthe new connector. Replace the existing terminals,then insert them into the new connector and jointhe connector together.





CONDUCTOR REPAIR

Conductor repairs are sometimes needed because of wire damage caused by electrical faults or by physical

abuse. Wires may be damaged electrically by shortcircuits between wires or from wires to ground. Fusiblelinks may melt from current overloads. Wires may bedamaged physically by scraped or cut insulation,chemical or heat exposure, or breaks caused duringtesting or component repairs.

WIRE SIZE

Choosing the proper size of wire when making circuitrepairs is critical. While choosing wires too thick for thecircuit will only make splicing a bit more difficult,choosing wires too thin may limit current flow to

unacceptable levels or even result in melted wires.Two size factors must be considered: wire gaugenumber and wire length.

• WIRE GAUGE NUMBER

Wire gauge numbers are determined by theconductor's cross-section area.

In the American Wire Gauge system, "gauge"numbers are assigned to wires of differentthicknesses. While the gauge numbers are notdirectly comparable to wire diameters and cross-section areas, higher numbers (16, 18, 20) areassigned to increasingly thinner wires and lower

numbers (1, 0, 2/0) are assigned to increasinglythicker wires. The chart shows AWG gauge numbersfor various thicknesses.

Wire cross-section area in the AWG system ismeasured in circular mils. A mil is a thousandth of aninch (0.001). A circular mil is the area of a circle 1 mil(0.001) in diameter.

In the metric system used worldwide, wire sizes arebased on the cross-section area in square millimeters(mm 2 ). These are not the same as AWG sizes incircular mils. The chart shows AWG size equivalentsfor various metric sizes.

• WIRE LENGTH

Wire length must be considered when repairingcircuits because resistance increases with longer lengths. For instance, a 16-gauge wire can carry an18-amp load for 10 feet without excessive voltagedrop. But, if the section of wiring being replaced isonly 3-feet long, an 18-gauge wire can be used.Never use a heavier wire than necessary, but - moreimportant - never use a wire that will be too small for the load.





WIRE REPAIRS

• Cut insulation should be wrapped with tape or

covered with heat-shrink tubing. In both cases,

overlap the repair about 1/2-inch on either side.

• If damaged wire needs replacement, make sure

the same or larger size is used. Also, attempt touse the same color. Wire strippers will removeinsulation without breaking or nicking the wirestrands.

• When splicing wires, make sure the battery is

disconnected. Clean the wire ends. Crimp andsolder them using rosin-core, not acid-core, solder.

• SOLDERING

Soldering joins two pieces of metal together with alead and tin alloy.

In soldering, the wires should be spliced together witha crimp. The less solder separating the wire strands,the stronger the joint.

• SOLDER

Solder is a mixture of lead and tin plus traces of other substances.

Flux core wire solder (wire solderwith a hollow center filled with flux) is recommended for electrical splices.

• SOLDERING FLUX

Soldering heats the wires. In so doing, it acceleratesoxidization, leaving a thin film of oxide on the wiresthat tends to reject solder. Flux removes this oxideand prevents further oxidation during the solderingprocess.

Rosin or resin-type flux must be used for all electricalwork. The residue will not cause corrosion, nor will itconduct electricity.

• SOLDERING IRONS

The soldering iron should be the right size for the job. An iron that is too small will require excessive time toheat the work and may never heat it properly. A low-wattage (25-100 W) iron works best for wiring repairs.

• CLEANING WORK

All traces of paint, rust, grease, and scale must beremoved. Good soldering requires clean, tight splices.





• TINNING THE IRON

The soldering iron tip is made of copper. Through thesolvent action of solder and prolonged heating, it will

pit and corrode. An oxidized or corroded tip will notsatisfactorily transfer heat from the iron to the work. Itshould be cleaned and tinned. Use a file and dressthe tip down to the bare copper. File the surfacessmooth and flat.

Then, plug the iron in. When the tip color begins tochange to brown and light purple, dip the tip in andout of a can of soldering flux (rosin type). Quicklyapply rosin core wire solder to all surfaces.

The iron must be at operating temperature to tinproperly. When the iron is at the proper temperature,solder will melt quickly and flow freely. Never try to

solder until the iron is properly tinned.

• SOLDERING WIRE SPLICES

Apply the tip flat against the splice. Apply rosin-corewire solder to the flat of the iron where it contacts thesplice. As the wire heats, the solder will flow throughthe splice.

• RULES FOR GOOD SOLDERING

1. Clean wires.

2. Wires should be crimped together.

3. Iron must be the right size and must be hot.

4. Iron tip must be tinned.

5. Apply full surface of soldering tip to the splice.

6. Heat wires until solder flows readily.

7. Use rosin-core solder.

8. Apply enough solder to form a secure splice.

9. Do not move splice until solder sets.

10. Place hot iron in a stand or on a protective pad.

11. Unplug iron as soon as you are finished.





Step 1. Identify the connector and terminal type.

1. Replacing Terminals

a. Identify the connector name, position of thelocking clips, the un-locking direction andterminal type from the pictures provided on thecharts.

Step 2. Remove the terminal from the connector.

1. Disengage the secondary locking device or terminal retainer.

a. Locking device must be disengaged before theterminal locking clip can be released and theterminal removed from the connector.

b. Use a miniature screwdriver or the terminal pickto unlock the secondary locking device.

2. Determine the primary locking system fromthe charts.

a. Lock located on terminal

b. Lock located on connector

c. Type of tool needed to unlock

d. Method of entry and operation





3. Remove terminal from connector byreleasing the locking clip.

a. Push the terminal gently into the connector and

hold it in this position.

b. Insert the terminal pick into the connector in thedirection shown in the chart.

c. Move the locking clip to the un-lock positionand hold it there.

NOTE: Do not apply excessive force to theterminal. Do not pry on the terminal with thepick.

d. Carefully withdraw the terminal from theconnector by pulling the lead toward the rear of the connector.

NOTE: Do not use too much force. If theterminal does not come out easily, repeatsteps (a.) through (d.).

4. Measure "nominal" size of the wire lead byplacing a measuring device, such as amicrometer or Vernier Caliper, across the

diameter of the insulation on the lead andtaking a reading.

5. Select the correct replacement terminal, withlead, from the repair kit.





6. Cut the old terminal from the harness.

a. Use the new wire lead as a guide for proper length.

NOTE: If the length of wire removed is notapproximately the same length as the newpiece, the following problems may develop:

Too short - tension on the terminal, splice, or the connector, causing an open circuit.

Too long - excessive wire near theconnector, may get pinched or abraded,causing a short circuit.

NOTE: If the connector is of a waterproof type,the rubber plug may be reused.

7. Strip insulation from wire on the harness andreplacement terminal lead.

a. Strip length should be approximately 8 to 10mm (3/8 in.).

NOTE: Strip carefully to avoid nicking or cuttingany of the strands of wire.

NOTE: If heat shrink tube is to be used, it must beinstalled at this time, sliding it over the end of onewire to be spliced. (See Step 3, 4. B. 1. for instructions on how to use heat shrink tube.)

NOTE: If the connector is a waterproof type, therubber plug should be installed on the terminal endat this time.





1. Select correct size of splice from the repair kit.

a. Size is based on the nominal size of the wire(three sizes are available).

Part Number Wire Size

Small 00204-34130 16-22 AWG1.0 - 0.2 mm

Medium 00204-34137 14-16 AWG2.0 - 1.0 mm

Large 00204-34138 10 - 12 AWG5.0 - 3.0 mm

2. Crimp the replacement terminal lead to theharness lead.

a. Insert the stripped ends of both thereplacement lead and the harness lead intothe splice, overlapping the wires inside thesplice.

NOTE: Do not place insulation in the splice,only stripped wire.

b. Do not use position marked "INS".

The crimping tool has positions marked for

insulated splices (marked "INS") that shouldnot be used, as they will not crimp the splicetightly onto the wires.

c. Use only position marked "NON INS".

1. With the center of the splice correctly placed

between the crimping jaws, squeeze thecrimping tool together until the contact pointsof the crimper come together.

NOTE: Make sure the wires and the spliceare still in the proper position beforeclosing the crimping tool ends. Use steadypressure in making the crimp.

2. Make certain that the splice is crimpedlightly.





3. Solder the completed splice using only rosincore solder.

a. Wires and splices must be clean.

b. A good mechanical joint must exist, becausethe solder will not hold the joint together.

c. Heat the joint with the soldering iron until thesolder melts when pressed onto the joint.

d. Slowly press the solder into the hot splice onone end until it flows into the joint and outthe other end of the splice.

NOTE: Do not use more solder than necessaryto achieve a good connection. There shouldnot be a "glob" of solder on the splice.

e. When enough solder has been applied,remove the solder from the joint and thenremove the soldering iron.

4. Insulate the soldered splice using one of thefollowing methods:

a. Silicon tape (provided in the wire repair kit)

1. Cut a piece of tape from the rollapproximately 25 mm (1 in.) long.

2. Remove the clear wrapper from the tape.

NOTE: The tape will not feel "sticky" on either side.

3. Place one end of the tape on the wire andwrap the tape tightly around the wire. Youshould cover one-half of the previous wrapeach time you make a complete turnaround the wire. (When stretched, thistape will adhere to itself.)

4. When completed, the splice should becompletely covered with the tape and thetape should stay in place. If both of these

conditions are not met, remove the tapeand repeat steps 1 through 4.

NOTE: If the splice is in the enginecompartment or under the floor, or in an areawhere there might be abrasion on the splicedarea, cover the silicon tape with vinyl tape.





b. Heat shrink tube (provided in the wire repair kit)

1. Cut a piece of the heat shrink tube that isslightly longer than the splice, and slightly

larger in diameter than the splice.

2. Slide the tube over the end of one wire tobe spliced. (THIS STEP MUST BE DONEPRIOR TO JOINING THE WIRESTOGETHER!)

3. Center the tube over the soldered splice.

4. Using a source of heat, such as a heat gun,gently heat the tubing until it has shrunktightly around the splice.

NOTE: Do not continue heating the tubing after

it has shrunk around the splice. It will onlyshrink a certain amount, and then stop. It willnot continue to shrink as long as you hold heatto it, so be careful not to melt the insulation onthe adjoining wires by trying to get the tubing toshrink further.

Step 4. Install the terminal into the connector.

1. If reusing a terminal, check that the lockingclip is still in good condition and in the proper

position.

a. If it is on the terminal and not in theproper position, use the terminal pick togently bend the locking clip back to theoriginal shape.

b. Check that the other parts of the terminalare in their original shape.





2. Push the terminal into the connector until youhear a "click".

NOTE: Not all terminals will give an audible

"click".

a. When properly installed, pulling gently on thewire lead will prove the terminal is locked inthe connector.

3. Close terminal retainer or secondary lockingdevice.

a. If the connector is fitted with a terminalretainer, or a secondary locking device, returnit to the lock position.

4. Secure the repaired wire to the harness.

a. If the wire is not in the conduit, or secured byother means, wrap vinyl tape around thebundle to keep it together with the other wires.





WIRE, TERMINAL A ND CONNECTOR REPAIR A SSIGNMENT NAME:

1. E x pla i n w h ich t y pe of w ir e i s u sed w h en cu rr en t flow i s hig h.

2. E xpla i n w h a t i s m ea n by sy st em pola r it y a n d how i s it u sed t od a y .

3. E x pl a in how t he col or s of t he w i r e i ns ul a t i on a r e us ed a nd g ive a n e xa m p le.

4. E x pl a i n how w i re is s iz ed , di ff er en t s i zi ng s y st em s , a nd p r ov ide ex a m pl es .

5. Name the cor rect t ype of solder used for elect r ica l repa i r repa i r and w hy

6. O ut l in e t h e pr oced ur e f or “ Tin n in g a n Ir on ” .

7. L is t t h e r ules for good s old er in g.

8. Out line in de t a i l t he cor rect p rocedure for spl icing a new wire end on .

9. When an d w hy is a hea t gun used?



General

The battery is the primary "source" of electricalenergy on Toyota vehicles. It stores chemicals, notelectricity. Two different types of lead in an acidmixture react to produce an electrical pressure. Thiselectrochemical reaction changes chemical energyto electrical energy.

Battery Functions

1. ENGINE OFF: Battery energy is used tooperate the lighting and accessory systems.

2. ENGINE STARTING: Battery energy is usedto operate the starter motor and to providecurrent for the ignition system during cranking.

3. ENGINE RUNNING: Battery energy may be

needed when the vehicle's electrical loadrequirements exceed the supply from the chargingsystem.

In addition, the battery also serves as a voltagestabilizer , or large filter, by absorbing abnormal,transient voltages in the vehicle's electrical system.Without this protection, certain electrical or electroniccomponents could be damaged by these highvoltages.

Battery Types

1. PRIMARY CELL: The chemical reaction totallydestroys one of the metals after a period of time.Small batteries for flashlights and radios areprimary cells.

2. SECONDARY CELLS: The metals and acid mixturechange as the battery supplies voltage. Themetals become similar, the acid strength weakens.

This is called discharging . By applying current tothe battery in the opposite direction, the batterymaterials can be restored. This is called charging .Automotive lead-acid batteries are secondary cells.

3. WET-CHARGED: The lead-acid battery is filled withelectrolyte and charged when it is built. Duringstorage, a slow chemical reaction will cause self-discharge. Periodic charging is required. For

Toyota batteries, this is every 5 to 7 months.

4. DRY-CHARGED: The battery is built, charged,washed and dried, sealed, and shipped withoutelectrolyte. It can be stored for 12 to .18 months.When put into use, it requires adding electrolyteand charging.

5. LOW-MAINTENANCE: Most batteries for Toyotavehicles are considered low-maintenancebatteries. Such batteries are built to reduceinternal heat and water loss. The addition of watershould only be required every 15,000 miles or so.

BATTERIES




Construction

1. CASE: Container which holds and protects allbattery components and electrolyte, separatescells, and provides space at the bottom forsediment (active materials washed off plates).

Translucent plastic cases allow checkingelectrolyte level without removing vent caps.

2. COVER: Permanently sealed to the top of thecase; provides outlets for terminal posts, ventholes for venting of gases and for batterymaintenance (checking electrolyte, adding water).

3. PLATES: Positive and negative plates have a gridframework of antimony and lead alloy. Activematerial is pasted to the grid ... brown-coloredlead dioxide (Pb02) on positive plates, gray-colored sponge lead (Pb) on negative plates. Thenumber and size of the plates determine currentcapability ... batteries with large plates or manyplates produce more current than batteries withsmall plates or few plates.

4. SEPARATORS: Thin, porous insulators (wovenglass or plastic envelopes) are placed betweenpositive and negative plates. They allow passageof electrolyte, yet prevent the plates from touchingand shorting out.

5. CELLS: An assembly of connected positive andnegative plates with separators in between iscalled a cell or element. When immersed inelectrolyte, a cell produces about 2.1 volts

(regardless of the number or size of plates).Battery cells are connected in series, so thenumber of cells determines the battery voltage. A"1 2 - volt" battery has six cells.

6. CELL CONNECTORS: Heavy, cast alloy metalstraps are welded to the negative terminal of one

cell and the positive terminal of the adjoining celluntil all six cells are connected in series.

7. CELL PARTITIONS: Part of the case, the partitionsseparate each cell.

8. TERMINAL POSTS: Positive and negative posts(terminals) on the case top have thick, heavycables connected to them. These cables connectthe battery to the vehicle's electrical system(positive) and to ground (negative).

9. VENT CAPS: Types include individual filler plugs,strip-type, or box-type. They allow controlled

release of hydrogen gas during charging (vehicleoperation). Removed, they permit checkingelectrolyte and, if necessary, adding water.

10. ELECTROLYTE: A mixture of sulfuric acid(H2SO4) and water (H2O). It reacts chemicallywith the active materials in the plates to create anelectrical pressure (voltage). And, it conducts theelectrical current produced by that pressure fromplate to plate. A fully charged battery will haveabout 36% acid and 64% water.

BATTERIES




CELL THEORYA lead-acid cell works by a simple principle: when twodifferent metals are immersed in an acid solution, achemical reaction creates an electrical pressure.One metal is brown-colored lead dioxide (Pb02). Ithas a positive electrical charge. The other metal is

gray colored sponge lead (Pb). It has a negativeelectrical charge. The acid solution is a mixture of sulfuric acid (H2SO4) and water (H20). It is called

electrolyte.If a conductor and a load are connected between thetwo metals, current will flow. This discharging willcontinue until the metals become alike and the acid isused up. The action can be reversed by sending

current into the cell in the opposite direction. Thischarging will continue until the cell materials arerestored to their original condition.

BATTERIES




ELECTROCHEMICAL REACTIONA lead-acid storage battery can be partiallydischarged and recharged many times. There arefour stages in this discharging/charging cycle.

1. CHARGED: A fully charged battery contains anegative plate of sponge lead (Pb), a positive plateof lead dioxide (Pb02), and electrolyte of sulfuric acid(H2SO4) and water (H20).

2. DISCHARGING: As the battery is discharging, theelectrolyte becomes diluted and the plates becomesulfated. The electrolyte divides into hydrogen (H2)and sulfate(S04) . The hydrogen (H2) combines withoxygen (0) from the positive plate to form more water(H20). The sulfate combines with the lead (Pb) inboth plates to form lead sulfate (PbS04)

3. DISCHARGED: In a fully discharged battery, bothplates are covered with lead sulfate (PbSO4) and theelectrolyte is diluted to mostly water (H2O).

4. CHARGING: During charging, the chemical actionis reversed. Sulfate (S04) leaves the plates andcombines with hydrogen (H2) to become sulfuric acid(H2SO4). Free oxygen (02) combines with lead (Pb)on the positive plate to form lead dioxide (Pb02).Gassing occurs as the battery nears full charge, andhydrogen bubbles out at the negative plates, oxygenat the positive.

BATTERIES




Capacity Ratings The battery must be capable of cranking the engineand providing adequate reserve capacity. Itscapacity is the amount of electrical energy thebattery can deliver when fully charged. Capacity isdetermined by the size and number of plates, thenumber of cells, and the strength and volume of electrolyte.

The most commonly used ratings are:

• Cold Cranking Amperes (CCA)

• Reserve Capacity (RC)

• Amp-Hours (AH)

• Power (Watts)

COLD-CRANKING AMPERES (CCA) The battery's primary function is to provide energy tocrank the engine during starting. This requires alarge discharge in a short time. The CCA Rating specifies, in amperes, the discharge load a fullycharged battery at 0˚F (-1 7.8˚C) can deliver for 30seconds while maintaining a voltage of at least 1.2volts per cell (7.2 volts total for a 12-volt battery).Batteries used on various Toyota vehicles have CCAratings ranging from 350 to 560 amps.

RESERVE CAPACITY (RC) The battery must provide emergency energy forignition, lights, and accessories if the vehicle's

charging system fails. This requires adequatecapacity at normal temperatures for a certain amountof time. The RC Rating specifies, in minutes, thelength of time a fully charged battery at 80˚F (26.7'C)can be discharged at 25 amps while maintaining avoltage of at least 1.75 volts per cell (10.5 volts totalfor a 12-volt battery). Batteries used on various

Toyota vehicles have RC ratings ranging from 55 to115 minutes.

AMP-HOURS (AH) The battery must maintain active materials on itsplates and adequate lasting power under light-loadconditions. This method of rating batteries is alsocalled the 20-hour discharge rating. Originalequipment batteries are rated in amp-hours. Theratings of these batteries are listed in the partsmicrofiche. The Amp-Hour Rating specifies, inamphours, the current the battery can provide for 20hours at 80˚F (26.7˚C) while maintaining a voltage of at least 1.75 volts per cell (10.5 volts total for a 12-volt battery). For example, a battery that can deliver 4amps for 20 hours is rated at 80 amp-hours (4 x 20 =80). Batteries used on various Toyota vehicles haveAH ratings ranging from 40 to 80 amp-hours.

POWER (WATTS) The battery's available cranking power may also bemeasured in watts. The Power Rating, in watts, is

determined by multiplying the current available by thebattery voltage at 0˚F (-1 7.8˚C). Batteries used onvarious Toyota vehicles have power ratings rangingfrom 2000 to 4000 watts.

BATTERIES




FACTORS AFFECTING CHARGINGFive factors affect battery charging by increasing itsinternal resistance and CEMF (counter-electromotiveforce produced by the electrochemical reaction):

1. TEMPERATURE: As the temperature decreases

the electrolyte resists charging. A cold battery willtake more time to charge; a warm battery, less time.Never attempt to charge a frozen battery.

2. STATE-OF-CHARGE: The condition of thebattery's active materials will affect charging. Abattery that is severely discharged will have hardsulfate crystals on its plates. The vehicle's chargingsystem may charge at too high of a rate to removesuch sulfates.

3. PLATE AREA: Small plates are charged fasterthan large plates. When sulfation covers most of theplate area, the charging system may not be able torestore the battery.

4. IMPURITIES: Dirt and other impurities in theelectrolyte increase charging difficulty.

5. GASSING: Hydrogen and oxygen bubbles form atthe plates during charging. As these bubble out, theywash away active material, cause water loss, andincrease charging difficulty.

BATTERIES




BATTERIES




Diagnosis and Testing

All batteries require routine maintenance to identifyand correct problems caused by physical abuse andlow electrolyte levels. A visual inspection canidentify such physical problems. A state-of-chargetest checks the electrolyte strength. And, electricaltesting identifies overcharging or underchargingproblems. These tests include a capacity, or heavy-load, test.

SAFETY FIRST!

When testing or servicing a battery, safety should beyour first consideration. The electrolyte containssulfuric acid. It can eat your clothes. It can burn yourskin. It can blind you if it gets in your eyes. It canalso ruin a car's finish or upholstery. If electrolyte is

splashed on your skin or in your eyes, wash it awayimmediately with large amounts of water. If electrolyteis spilled on the car, wash it away with a solution of baking soda and water.

When a battery is being charged, either by thecharging system or by a separate charger, gassingwill occur. Hydrogen gas is explosive. Any flame orspark can ignite it. If the flame travels into the cells,the battery may explode.

Safety precautions include:

• Wear gloves and safety glasses.

• Remove rings, watches, other jewelry.

• Never use spark-producing tools near a battery.

• Never lay tools on the battery.

• When removing cables, always remove the groundcable first.

• When connecting cables, always connect theground cable last.

• Do not use the battery ground terminal when

checking for ignition spark.

• Be careful not to get electrolyte in your eyes or onyour skin, the car finish, or your clothing.

• If you have to mix battery electrolyte, pour the acidinto the water - not the water into the acid.

• Always follow the recommended procedures forbattery testing and charging and for jump startingan engine.

CARE OF ELECTRONICS

Disconnecting the battery will erase the memory onelectronic devices. Write down trouble codes and

programmed settings before disconnecting the

battery.

Also, to prevent damage to electronic components:

• Never disconnect the battery with the ignition ON.

• Never use an electric welder without the batterycables disconnected.

• Never reverse battery polarity.

BATTERIES




VISUAL INSPECTION

Battery service should begin with a thorough visualinspection. This may reveal simple, easily correctedproblems, or problems that might require batteryreplacement.

1 . Check for cracks in the battery case and forbroken terminals. Either may allow electrolyteleakage. The battery must be replaced.

2. Check for cracked or broken cables orconnections. Replace, as needed.

3. Check for corrosion on terminals and dirt or acidon the case top. Clean the terminals and case topwith a mixture of water and baking soda orammonia. A wire brush is needed for heavycorrosion on the terminals.

4. Check for a loose battery hold-down and loosecable connections. Tighten, as needed.

5. Check the level of electrolyte. The level can beviewed through the translucent plastic case or byremoving the vent caps and looking directly intoeach cell. The proper level is 1/2" above the

separators. If necessary, add distilled water toeach low cell. Avoid overfilling. When water isadded, always charge the battery to make surethe water and acid mix.

6. Check for cloudy or discolored electrolyte causedby overcharging or vibration. This could cause highself discharge. The problem should be correctedand the battery replaced.

7. Check the condition of plates and separators.Plates should alternate dark (+) and light (-). If allare light, severe undercharging is indicated.Cracked separators may allow shorts. The batteryshould be replaced. An undercharging problemshould be corrected.

BATTERIES




8. Check the tension and condition of the alternatordrive belt. A loose belt must be tightened. It willprevent proper charging. A belt too tight willreduce alternator life. It should be loosened tospecs. A frayed or glazed belt will fail duringoperation. Replace it.

NOTE: Approved Equipment tension gauge:Nippondenso, BTG-20 (SST) Borroughs BT-33-73F

9. Check for battery drain or parasitic loads usingan ammeter. Connect the ammeter in seriesbetween the battery negative terminal and groundcable connector. Toyota vehicles typically showless than .020 amp of current to maintainelectronic memories ... a reading of more than.035 amp is unacceptable. If the ammeter readsmore than .035 amp, locate and correct the causeof excessive battery drain.

10. Check for battery discharge across the top of thebattery using a voltmeter. Select the low voltagescale on the meter, connect the negative (black)test lead to the battery's negative post, andconnect the positive (red) test lead to the top of the battery case. If the meter reading is morethan 0.5 volt, clean the case top using a solutionof baking soda and water.

BATTERIES




STATE-OF-CHARGE TEST The state-of-charge test checks the battery'schemical condition. One method uses a hydrometerto measure the specific gravity of the electrolyte.Another method uses a digital voltmeter to check thebattery's open circuit voltage and, for a general

indication of the battery's condition, check theindicator eye (if the battery has one) or check theheadlamp brightness during starting.

Specific GravitySpecific gravity means exact weight. The hydrometercompares the exact weight of electrolyte with that of water. Strong electrolyte in a charged battery isheavier than weak electrolyt e in a dischargedbattery.

By weight, the electrolyte in a fully charged battery isabout 36% acid and 64% water. The specific gravityof water is 1.000. The acid is 1.835 times heavierthan water, so its specific gravity is 1.835. Theelectrolyte mixture of water and acid has a specificgravity of 1.270 is usually stated as "twelve andseventy."By measuring the specific gravity of the electrolyte,you can tell if the battery is fully charged, requirescharging, or must be replaced. It can tell you if thebattery is charged enough for the capacity, or heavy-load test.

TEST PROCEDURE: The following steps outline atypical procedure for performing a state-of-chargetest:1 . Remove vent caps or covers from the battery cells.2. Squeeze the hydrometer bulb and insert thepickup tube into the cell closest to the battery'spositive (+) terminal.3. Slowly release the bulb to draw in only enough

electrolyte to cause the float to rise. Do notremove the tube from the cell.

4. Read the specific gravity indicated on the float. Besure the float is drifting free, not in contact with thesides of top of the barrel. Bend down to read thehydrometer a eye level. Disregard the slightcurvature of liquid on the float.

5. Read the temperature of the electrolyte.6. Record your readings and repeat the procedure for

the remaining cells.

TEMPERATURE CORRECTION: The specific gravitychanges with temperature. Heat thins the liquid, andlowers the specific gravity. Cold thickens the liquid,and raises the specific gravity. Hydrometers areaccurate at 80-F (26.7˚C). If the electrolyte is at anyother temperature, the hydrometer readings must beadjusted. Most hydrometers have a built-inthermometer and conversion chart. Refer to thetemperature correction chart. For each 1 O F (5.5 C)above 80˚F (26.7˚C), ADD 0.004 to your reading.

BATTERIES




TEST RESULTS: Specific gravity readings tell a lotabout battery condition.

1. A fully charged battery will have specific gravityreadings around 1.265.

2. Specific gravity readings below 1.225 usually

mean the battery is run down and must becharged.3. Readings around 1.190 indicate that sulfation is

about to begin. The battery must be charged.4. Readings of 1.155 indicate severe discharge.

Slow charging is required to restore activematerials.

5. Readings of 1.120 or less indicate that the batteryis completely discharged. It may requirereplacement, but slow charging may restore somebatteries in this condition.

6. A difference of 50 points (0.050) or more betweenone or more cells indicates a defective battery. Itshould be replaced.

7. When the specific gravity of all cells is above1.225 and the variation between cells is less than50 points, the battery can be tested under load.

Open-Circuit VoltageAn accurate digital voltmeter is used to check thebattery's open-circuit voltage:

1 . If the battery has just been charged, turn on theheadlamps for one minute to remove any surfacecharge.

2. Turn headlamps off and connect the voltmeteracross the battery terminals.

3. Read the voltmeter. A fully charged battery will

have an open-circuit voltage of at least 12.6 volts.A dead battery will have an open-circuit voltage of less than 12.0 volts.

Indicator Eye Toyota original-equipment batteries have an indicatoreye for electrolyte level and specific gravity. If theeye shows red, the electrolyte level is low or thebattery is severely discharged. If some blue isshowing, the level is okay and the battery is at least25% charged.

NOTE: The indicator eye should be used only as ageneral indication of electrolyte level and strength.

BATTERIES




HEAVY-LOAD TESTWhile an open circuit voltage test determines thebattery's state of charge, it does not measure thebattery's ability to deliver adequate cranking power.A capacity, or heavy-load , test does. A Sun VAT-40tester is used. If another type of tester is used, follow

the manufacturer's recommended procedure.

The following steps outline a typical procedure forload testing a battery:

1. Test the open circuit voltage. The battery must beat least half charged. If the open circuit voltage isless than 12.4v, charge the battery.

2. Disconnect the battery cables, ground cable first.3. Prepare the tester:

• Rotate the Load Increase control to OFF.• Check each meter's mechanical zero. Adjust, if necessary.

• Connect the tester Load Leads to the batteryterminals; RED to positive, BLACK to negative.

• Set Volt Selector to INT 18V. Tester voltmetershould indicate battery open-circuit voltage.

NOTE: Battery open-circuit voltage should be at least12.4 volts (75% charged). If not, the battery requirescharging.

• Set Test Selector to #2 CHARGING.• Adjust ammeter to read ZERO using the electrical

Zero Adjust control.4. Connect the clamp-on Amps Pickup around either

tester load cable (disregard polarity).

5. Set the Test Selector Switch to #1 STARTING.6. Load the battery by turning the Load Increase

control until the ammeter reads 3 times the amp-hour (AH) rating or one-half the cold-crankingampere (CCA) rating.

7. Maintain the load for no more than 15 seconds and note the voltmeter reading.

8. Immediately turn the Load Increase control OFF.9. If the voltmeter reading was 10.0 volts or more, the

battery is good. If the reading is 9.6 to 9.9 volts,the battery is serviceable, but requires furthertesting. Charge and re-test. If the reading wasbelow 9.6 volts, the battery is either dischargedor defective.

NOTE: Test results will vary with temperature. Lowtemperatures will reduce the reading. The batteryshould be at operating temperature.

BATTERIES




Battery ServiceBattery service procedures include charging,cleaning, jump starting, and replacement. Follow therecommended procedures.

CHARGINGA battery in good condition may occasionally fail tocrank the engine fast enough to make it start. In suchcases, the battery may require charging.

All battery chargers operate on the same principle: anelectric current is applied to the battery to reverse thechemical action in the cells. Never connect ordisconnect leads with the charger turned ON. Followthe battery charger manufacturer's instructions. And,do not attempt to charge a battery with frozenelectrolyte.

When using a battery charger, always disconnect the

battery ground cable first. This will minimize thepossibility of damage to the alternator or to electroniccomponents. Otherwise, use a charger with polarityprotection that prevents reverse charging.

The battery can be considered fully charged when allcells are gassing freely and when there is no changein specific gravity readings for more than one hour.

BATTERIES




Fast ChargingFast charging is used to charge the battery for ashort period of time with a high rate of current. Fastcharging may shorten battery life. If time allows, slowcharging is preferred. Some low maintenancebatteries cannot be fast charged.

1. Preparation for charging.• Clean dirt, dust, or corrosion off the battery; if

necessary, clean the terminals.• Check the electrolyte level and add distilled

water if needed.• If the battery is to be charged while on the

vehicle, be sure to disconnect both (-) (+)terminals.

2. Determine the charging current and time for fastcharging.• Some chargers have a test device for

determining the charging current and required

time.• If the charger does not have a test device, refer

to the chart below to determine current and time.

3. Using the charger:• Make sure that the main switch and timer switchare OFF and the current adjust switch is at theminimum position.

• Connect the positive lead of the charger to thebattery positive terminal (+) and the negativelead of the charger to the battery negativeterminal (-).

• Connect the charger's power cable to the electricoutlet.

• Set the voltage switch to the correct batteryvoltage.

• Set the main switch at ON.• Set the timer to the desired time and adjust the

charging current to the predeterminedamperage.

4. After the timer is "off," check the chargedcondition using a voltmeter.• Correct Voltage: 12.6 volts or higher.

If the voltage does not increase, or if gas is notemitted no matter how long the battery is charged,there may be a problem with the battery, such as aninternal short.

5. When the voltage reaches the proper reading:• Set the current adjust switch to minimum.• Turn off the main switch of the charger.• Disconnect the charger cables from the battery

terminals.• Wash the battery case to clean off the acidemitted.

Slow ChargingHigh charging rates are not good for completelycharging a battery. To completely charge a battery,slow charging with a low current is required.Slow charging procedures are the same as those forfast charging, except for the following:

1. The maximum charging current should be less than1 1/10th of the battery capacity. For instance, a 40AH battery should be slow charged at 4 amps orless.

2. Set the charger switch to the slow position (if provided).

3. Readjust the current control switch from time totime while charging.

4. As the battery gets near full charge, hydrogen gasis emitted. When there is no further rise in battery

voltage for more than one hour, the battery iscompletely charged.• Battery Voltage: 12.6 volts or higher

BATTERIES




CLEANINGCleaning the battery will aid your visual inspectionand reduce the possibility of current leakage. Thebattery case can be cleaned with a brush and dilutedammonia or soda solution. Avoid getting the solutionin the cells. The battery terminals and cable

connections can be cleaned with the cleaning tool(brush) made for that purpose. Remove all corrosionand oxidation, both common causes of highresistance.

JUMP STARTINGWhen jump starting a dead battery with a boosterbattery, proper connections prevent sparks. First,connect the two positive terminals. Then, connectone end of the jumper cable to the negative terminal

of the booster battery. And, connect the other end toa good ground away from the dead battery. If a sparkoccurs, it won't be near the battery.

BATTERY REPLACEMENTIf a battery requires replacement: use a cable pullerto remove terminal clamps; unfasten the battery hold-down; lift the battery from its carrier with the propertool; wash and paint corroded parts; replace any

damaged parts of the hold-down, support tray, orcables; and select and install a battery of the propersize and capacity rating.

Taken with permission from the Toyota BasicElectrical Course #622,

BATTERIES




SELF TEST This brief self-test will help you measure yourunderstanding of The Battery. The style is thesame as that used for A.S.E. certification tests.

The answers to this self test are shown on next

page.

1. The amount of current a battery can produce iscontrolled by the:

A. plate thicknessB. plate surface areaC. strength of acidD. discharge of load

2. How many volts are produced in each cell of abattery?

A. 2.1B. 6. 0C. 9.6D. 12.0

3. The plates of a discharged battery are:

A. two similar metals in the presence of anelectrolyte

B. two similar metals in the presence of waterC. two dissimilar metals in the presence of an

electrolyteD. two dissimilar metals in the presence of

water

4. A battery's reserve capacity is measured in:

A. amperesB. waftsC. amp-HoursD. minutes

5. Severe battery undercharging is indicated if:

A. active materials are washed off theplatesB. the terminals are corrodedC. the plates (+and -) are both very light

coloredD. the electrolyte is cloudy

6. To check for battery drain, you would connectan ammeter between the:

A. battery and alternatorB. battery and (-) terminalsC. battery terminal and ground cableD. battery terminal and ground cable

7. What is the state of charge of a battery that hasa specific gravity of 1.190 at 80˚F (26.7'C)?

A. Completely dischargedB. About 1/2 chargedC. About 3/4 chargedD. Fully charged

8. A battery heavy-load test discharges the batteryfor:

A. 5 secondsB. 10 secondsC. 15 secondsD. 20 seconds

9. When performing a battery capacity test on a12-volt battery, the voltage should not fall below:

A. 12.0 voltsB. 10.6 voltsC. 9.6 voltsD. 8.6 volts

10. The preferred method of recharging a "dead"battery is:

A. fast chargingB. slow chargingC. cycling the batteryD. with a VAT-40

BATTERIES




SELF-TEST ANSWERS

For the preceding self-test on The Battery,the following best complete the sentence oranswer the question. In cases where youmay disagree with the choice - or may simplywant to reinforce your understanding -please review the appropriate workbookpage or pages noted.

1 . "B" - The number and size of the platesdetermine current capability. (Page 2.)

2. "A" - When immersed in electrolyte, a cellproduces about 2.1 volts (regardless of thenumber of size of plates). (Page 2.)

3. "B" - In a fully discharged battery, bothplates are covered with lead sulfate and theelectrolyte is diluted to mostly water. (Page4.)

4. "D" - The Reserve Capacity rating is thelength of time, in minutes, a fully chargedbattery at 80'F (26.70C) can be discharged at25 amps while maintaining a voltage of at

least 1.75 volts per cell. (Page 5.)5. "C" - Plates should alternate dark (+) andlight It all are light, severe undercharging isindicated. (Page 9.)

6. "D" - Check for battery drain using anammeter between the battery negativeterminal and ground cable connector. (Page10.)

7. "B" - Specific gravity readings around1.190 indicate that sulfation is about tobegin. The battery is about 50% charged,and requires charging. (Page 12.)

8. "C" - In a battery load test, maintain theload for no more than 15 seconds and notethe voltmeter reading. (Page 13.)

9. "C" - In a battery capacity or heavy-load test,if the voltmeter reading falls below 9.6 volts,the battery is either discharged or defective.(Page 13.)

10. "B" - Slow charging is preferred. (Page15.)

BATTERIES




BATTERIES ASSIGNMENT NAME:

1. Describe the basic construction of a lead-acid battery.

2. Explain what materials are used to make up the: positive plate, negative plate, andelectrolyte.

3. Describe the basic chemical operation of a single cell that makes a battery.

4. List the voltage output of both a single battery cell and a six cell automotivebattery. Be exact.

5. Explain the four basic battery “capacity ratings” systems.

6. List the gases that are produced during the charging process from both the positive andthe negative plates.

7. Explain why repeated “overcharging” or “cycling” is harmful to a battery.

8. List the three basic battery tests / inspections that can be performed.

9. List ten (10) items inspected while performing a “visual inspection”.

10. Explain the terms “battery drain” and “parasitic loads”.

11. Describe the procedure of checking parasitic drain on a car.

12. List the maximum parasitic drain allowed.

13. Describe why and how baking soda is used on an automotive battery.

14. List two methods of checking a battery’s “state of charge.

15. List the specific gravity readings of a battery that has the following states of

charge: 100%, 50%, 0%.

16. Explain the term “specific gravity” and how it is measured.

17. List the open circuit voltages of a battery with the following states of charge 100%, 50%, 0%.

18. Describe the “open circuit voltage” test procedure.

19. What is the minimum charge a battery needs to perform a Heavy Load Test.

20. Explain in detail the “Heavy Load” or “Capacity” test procedure.

21. What is the maximum time a Heavy Load Test should be performed?

22 How much of a load is placed on a battery that has a 500 CCA rating?

23. What action should be taken if battery voltage drops to 8.7 volts during a heavy load test?What if the voltage was 10.3 volts?



General

Starting the engine is possibly the most importantfunction of the vehicle's electrical system. Thestarting system performs this function by changing

electrical energy from the battery to mechanicalenergy in the starting motor. This motor thentransfers the mechanical energy, through gears, tothe flywheel on the engine's crankshaft. Duringcranking, the flywheel rotates and the air-fuelmixture is drawn into the cylinders, compressed,and ignited to start the engine. Most enginesrequire a cranking speed of about 200 rpm.

Toyota Starting SystemsTwo different starting systems are used on Toyotavehicles. Both systems have two separateelectrical circuits ... a control circuit and a motor

circuit. One has a conventional starting motor .

This system is used on most older-model Toyotas. The other has a gear reduction starting motor .This system is used on most current Toyotas. Aheavy-duty magnetic switch, or solenoid, turnsthe motor on and off. It is part of both the motor

circuit and the control circuit.

Both systems are controlled by the ignitionswitch and protected by a fusible link. On somemodels, a starter relay is used in the starter controlcircuit. On models with automatic transmission, aneutral start switch prevents starting with thetransmission in gear. On models with manualtransmission, a clutch switch prevents startingunless the clutch is fully depressed. On 4WD Truckand 4-Runner models, a safety cancel switch allows starting on hills without the clutchdepressed. It does so by establishing an alternate

path to ground.

TOYOTA STARTING SYSTEMS




Starting System Operation





Starting Motor Construction

GENERAL

The starter motors used on Toyota vehicles have a

magnetic switch that shifts a rotating gear (piniongear) into and out of mesh with the ring gear onthe engine flywheel. Two types of motors areused: conventional and gear reduction. Both arerated by power output in kilowatts (KW) ... thegreater the output, the greater the cranking power.

CONVENTIONAL STARTER MOTOR The conventional starter motor contains thecomponents shown. The pinion gear is on thesame shaft as the motor armature and rotates

at the same speed. A plunger in the magneticswitch (solenoid) is connected to a shift lever.When activated by the plunger, the shift lever pushes the pinion gear and causes it to mesh with

the flywheel ring gear . When the engine starts,an over-running clutch disengages the piniongear to prevent engine torque from ruining thestarting motor.

This type of starter was used on most 1975 andolder Toyota vehicles. It is currently used oncertain Tercel models. Typical output ratings are0.8, 0.9, and 1.0KW. In most cases, replacementstarters for these older motors are gear-reductionmotors.





GEAR-REDUCTION STARTER MOTOR

The gear-reduction starter motor contains thecomponents shown. This type of starter has acompact, high-speed motor and a set of reduction

gears. While the motor is smaller and weighs lessthan conventional starting motors, it operates athigher speed. The reduction gears transfer thistorque to the pinion gear at 1/4 to 1/3 the motor speed. The pinion gear still rotates faster than thegear on a conventional starter and with muchgreater torque (cranking power).

The reduction gear is mounted on the same shaftas the pinion gear. And, unlike in the conventional

starter, the magnetic switch plunger acts directlyon the pinion gear (not through a drive lever) topush the gear into mesh with the ring gear.

This type of starter was first used on the 1973

Corona MKII with the 4M, six cylinder engine. It isnow used on most 1975 and newer Toyotas.Ratings range from 0.8KW on most Tercels andsome older models to as high as 2.5KW on thediesel Corolla, Camry and Truck. The cold-weather package calls for a 1.4KW or 1.6KW starter, whilea 1.0KW starter is common on other models.

The gear-reduction starter is the replacementstarter for most conventional starters.





Starting Motor Operation

CONVENTIONAL STARTER MOTOR

IGNITION SWITCH IN "ST"

• Current flows from the battery through terminal"50" to the hold-in and pull-in coils. Then, from thepull-in coil, current flows through terminal "C" tothe field coils and armature coils.

• Voltage drop across the pull-in coil limits thecurrent to the motor, keeping its speed low.

• The solenoid plunger pulls the drive lever to meshthe pinion gear with the ring gear.

• The screw spline and low motor speed help the

gears mesh smoothly.

PINION AND RING GEARS ENGAGED

• When the gears are meshed, the contact plate onthe plunger turns on the main switch by closingthe connection between terminals "30" and "C."

• More current goes to the motor and it rotates withgreater torque (cranking power).

• Current no longer flows in the pull-in coil. Theplunger is held in position by the hold-in coil'smagnetic force.

IGNITION SWITCH IN "ON"

• Current no longer flows to terminal "50," but themain switch remains closed to allow current flowfrom terminal "C" through the pull-in coil to thehold-in coil.

• The magnetic fields in the two coils cancel each

other, and the plunger is pulled back by the returnspring.

• The high current to the motor is cut off and thepinion gear disengages from the ring gear.

• A spring-loaded brake stops the armature.





GEAR-REDUCTION STARTER MOTOR

IGNITION SWITCH IN "ST"

• Current flows from the battery through terminal

"50" to the hold-in and pull-in coils. Then, fromthe pull-in coil, current flows through terminal "C"to the field coils and armature coils.

• Voltage drop across the pull-in coil limits thecurrent to the motor, keeping its speed low.

• The magnetic switch plunger pushes the piniongear to mesh with the ring gear.

• he screw and low motor speed help thegears mesh smoothly.

PINION AND RING GEARS ENGAGED

• When the gears are meshed, the contact plate onhe plunger turns on the main switch by closingthe connection between terminals "30" and "C."

• More current goes to the motor and it rotates withgreater torque.

• Current no longer flows in the pull-in coil. Theplunger is held in position by the hold-in coil'smagnetic force.

IGNITION SWITCH IN "ON"

• Current no longer flows to terminal "50," but themain switch remains closed to allow currentflow from terminal "C" through the pull-in coil tothe hold-in coil.

• The magnetic fields in the two coils cancel eachother, and the plunger is pulled back by thereturn spring.

• The high current to the motor is cut off and thepinion gear disengages from the ring gear.

• The armature has less inertia than the one in aconventional starter. Friction stops it, so a brakeis not needed.





OVER-RUNNING CLUTCH

Both types of starter motors used on Toyotastarting systems have a one-way clutch, or over-running clutch. This clutch prevents damage to the

starter motor once the engine has been started. Itdoes so, by disengaging its housing (whichrotates with the motor armature) from an inner

race which is combined with the pinion gear.Spring loaded wedged rollers are used.

Without an over-running clutch, the starter motor would be quickly destroyed if engine torque wastransferred through the pinion gear to the armature.






The starting system requires little maintenance.Simply, keep the battery fully charged and allelectrical connections clean and tight.

Diagnosis of starting system problems is relativelyeasy. The system combines electrical andmechanical components. The cause of a startingproblem may be electrical (e.g., faulty switch) or mechanical (e.g., wrong engine oil or a faultyflywheel ring gear).

Specific symptoms of starting system problemsinclude:

• The engine will not crank;

• The engine cranks slowly;

• The starter keeps running;

• The starter spins, but the engine will not crank;and,

• The starter does not engage or disengageproperly.

For each of these problems, refer to the chartbelow for the possible causes and needed actions.Diagnosis starts with a thorough visual inspection.Testing includes: a starter motor current draw test,starter circuit voltage drop tests, operational andcontinuity checks of control components, andstarter motor bench tests.





VISUAL INSPECTION

A visual inspection of the starting system canuncover a number of simple, easy-to-correctproblems.

• SAFETY FIRST: The same safety considerationsused in checking the battery apply here. Removerings, wristwatch, other jewelry that might contactbattery terminals. Wear safety glasses andprotective clothing. Be careful not to spillelectrolyte and know what to do if electrolyte getsin your eyes, on your skin or clothing, or on thecar's finish. Write down programmed settings onelectronic components. Avoid causing sparks.

• STARTING PERFORMANCE: Check the startingperformance. Problem symptoms, possible causes,

and needed actions are shown in the chart on theprevious page.

• BATTERY CHECKS: Inspect the battery for corrosion, loose connections. Check theelectrolyte level, condition of the plates andseparators, and state of charge (specific gravity or open-circuit voltage). Load test the battery. It must

be capable of providing at least 9.6 volts duringcranking.

STARTER CABLES: Check the cable condition andconnections. Insulation should not be worn or damaged. Connections should be clean and tight.

STARTER CONTROL CIRCUIT: Check theoperation of the ignition switch. Current should besupplied to the magnetic switch when the ignition is"on" and the clutch switch or neutral start switch isclosed. Faulty parts that prevent cranking can belocated using a remote-control starter switch and a

jumper wire. Use the "split half" diagnosis method.Ohmmeter checks can also identify componentproblems.





CURRENT DRAW TEST A starter current draw test provides a quick checkof the entire starting system. With the Sun VAT-40tester, it also checks battery's cranking voltage. If another type of tester is used, follow the

manufacturer's recommended procedure.

The starting current draw and cranking voltageshould meet the specifications listed for the Toyotamodel being tested. Typical current draw specsare 130-150 amps for 4-cylinder models and 175amps for 6-cylinder models. Cranking voltagespecs range from 9.6 to 11 volts. Always refer tothe correct repair manual. Only perform the testwith the engine at operating temperature.

The following steps outline a typical procedure for performing a current draw test on a starting

system:1. This test should be made only with a

serviceable battery. The specific gravityreadings at 800˚F should average at least 1. 190(50% charged). Charge the battery, if necessary.

2. Prepare the tester:

• Rotate the Load Increase control to OFF.

• Check each meter's mechanical zero. Adjust, if necessary.

• Connect the tester Load Leads to the battery

terminals; RED to positive, BLACK to negative.

NOTE: Battery open-circuit voltage should be atleast 12.2 volts (50% charged). If not, the batteryrequires charging.

• Set Volt Selector to INT 18V. Tester voltmeter should indicate battery open-circuit voltage.

• Set Test Selector to #2 CHARGING.

• Adjust ammeter to read ZERO using the electricalZero Adjust control.

3. Connect the clamp-on Amps Pickup around thebattery ground cable or cables.

4. Make sure all lights and accessories are off andvehicle doors are closed.

5. Set the Test Selector switch to #1 STARTING.

6. Disable the ignition so the engine does not startduring testing.

7. Crank the engine, while observing the tester ammeter and voltmeter.

• Cranking speed should be normal (200-250 rpm).

• Current draw should not exceed the maximumspecified.

• Cranking voltage should be at or above theminimum specified.

8. Restore the engine to starting condition andremove tester leads.

TEST RESULTS: High current draw and lowcranking speed usually indicate a faulty starter.High current draw may also be caused by engineproblems. A low cranking speed with low current

draw, but high cranking voltage, usually indicatesexcessive resistance in the starter circuit.Remember that the battery must be fully chargedand its connections tight to insure accurate results.





VOLTAGE-DROP TESTS

Voltage-drop testing can detect excessiveresistance in the starting system. High resistancein the starter motor circuit (power side or ground

side) will reduce current to the starting motor. Thiscan cause slow cranking speed and hard starting.High resistance in the starter control circuit willreduce current to the magnetic switch. This cancause improper operation or no operation at all.

A Sun VAT-40 tester or separate voltmeter can beused. The following steps outline a typicalprocedure for performing voltage-drop tests on thestarting system:

Motor Circuit (insulated Side)1. If using the Sun VAT-40, set the Volt Selector to

EXT 3V. For other voltmeters, use a low scale.

2. Connect the voltmeter leads ... RED to thebattery positive (+) terminal, BLACK to terminal"C" on the starter motor magnetic switch.

3. Disable the ignition so the engine cannot startduring testing.

NOTE: On models with the Integrated Ignition Assembly, disconnect the "IIA" plug. On others,disconnect the power plug to the remote igniter assembly (black-orange wire).

4. Crank the engine and observe the voltmeter.Less than 0.5 volt indicates acceptableresistance. More than 0.5 volt indicatesexcessive resistance. This could be caused bya damaged cable, poor connections, or adefective magnetic switch.

5. If excessive resistance is indicated, locate thecause. Acceptable voltage drops are 0.3 voltacross the magnetic switch, 0.2 volts for the

cable, and zero volts for the cable connection.Repair or replace components, as needed.





Motor Circuit (Ground Side)1. Connect the voltmeter leads ... RED to the starter

motor housing, BLACK to the battery ground (-)terminal.

2. Crank the engine and observe the voltmeter.Less than 0.2 volt indicates acceptableresistance. More than 0.2 volt indicatesexcessive resistance. This could be caused bya loose motor mount, a bad battery ground, or aloose connection. Repair or replace componentsas necessary. Make sure engine-to-bodyground straps are secure.

Control Circuit1. Connect the voltmeter leads ... RED to the

battery positive (+) terminal, BLACK to terminal"50" of the starting motor.

2. On vehicles with automatic transmission, placethe lever in Park or Neutral. On vehicles withmanual transmission, depress the clutch.

(NOTE: A jumper wire could be used to bypasseither of these switches).

3. Crank the engine and observe the voltmeter.Less than .5 volt is acceptable. If the currentdraw was high or cranking speed slow, thestarter motor is defective. More than .5 voltindicates excessive resistance. Isolate thetrouble and correct the cause.

4. Check the neutral start switch or clutch switchfor excessive voltage drop. Also check theignition switch. Adjust or replace a defectiveswitch, as necessary.

5. An alternate method to checking the voltage dropacross each component is to leave the voltmeter connected to the battery (+) terminal and move

the voltmeter negative lead back through thecircuit toward the battery. The point of highresistance is found between the point wherevoltage drop fell within specs and the point lastchecked.





COMPONENT TESTS

For the various tests on starting systemcomponents, refer to the appropriate Toyota repair manual for testing procedures and specifications.

Ignition Switch and Key

The ignition switch should be checked bothmechanically as well as electrically. Make sure theswitch turns smoothly, without binding. And, checkthe ignition key for wear or metal chips that mightcause the switch to stick in the "start" position.Some duplicate keys have caused this problem. If an electrical problem is suspected, disconnect thebattery and check the switch for proper operationand continuity using an ohmmeter.

Starter Relay

• Continuity Check: Using an ohmmeter, check for continuity between terminals 1 and 3, and, for nocontinuity, between terminals 2 and 4. Replacethe relay if continuity is not as specified.

• Operational Check: Apply battery voltage acrossterminals 1 and 3 and check for continuitybetween terminals 2 and 4. Replace the relay if operation is not as specified.

Neutral Start Switch

If the engine will start with the shift selector in anyrange other than "N" or "P," adjust the switch. First,loosen the switch bolt and set the selector to "N."Then, disconnect the switch connector andconnect an ohmmeter between terminals 2 and 3.

Adjust the switch until there is continuity. (Refer toappropriate Service Manual for specific vehicleprocedures.)





Clutch Start Switch

Follow the procedure given in Toyota repair manuals for checking pedal height and freeplay.Then, check the switch for proper operation andcontinuity. Using an ohmmeter on the switchconnector, there should be continuity when theswitch is ON (clutch depressed) and no continuitywhen the switch is OFF (clutch not depressed). If continuity is not as specified, replace the switch.

Safety Cancel Switch

• Continuity Checks: Using an ohmmeter, thereshould be no continuity between terminals 2 and1, 3 and 1, or 2 and 3. If there is continuity,replace the switch.

• Operational Checks: Connect a battery betweenterminals 3 and 1 as shown. No continuity shouldbe seen between terminals 1 and 2. But, whenthe switch is pushed "on," there should becontinuity. If operation is not as specified, replacethe safety cancel switch.





SELF TESTThis brief self-test will help you measure your understanding of The Starting System. The style isthe same as that used for A.S.E. certification tests.The answers to this self test are shown on next

page.

1. The starting system has two circuits. They arethe:

A. motor circuit and ignition circuitB. insulated circuit and power circuitC. motor circuit and control circuitD. ground circuit and control circuit

2. A basic starter control circuit energizes themagnetic switch through the ignition switch andthe:

A. solenoidB. neutral start switchC. starter clutchD. regulator

3. On a Toyota gear-reduction starter, the plunger in the magnetic switch:

A. pulls a drive lever to mesh the gearsB. pushes the pinion gear into mesh with the

ring gear C. is held in place by the pull-in coilD. disengages the pinion gear from the starter

armature

4. When an engine starts, the pinion gear isdisconnected from the starter by the:

A. magnetic switchB. plunger C. over-running clutchD. switch return spring

5. If the engine cranks too slow to start, the

problem may be caused by:

A. engine problemsB. a faulty neutral start switchC. an open relay in the control circuitD. a damaged pinion gear

6. If a starter motor spins but does not engage andcrank the engine, the problem is most likelycaused by a bad:

A. magnetic switchB. over-running clutchC. positive battery cableD. ignition switch

7. When performing a starter current draw test,low current draw usually indicates:

A. high resistanceB. a bad starter C. a discharged batteryD. a short in the starter

8. When performing a starter current draw test,

high current draw usually indicates:

A. a discharged batteryB. high resistanceC. battery terminal corrosionD. engine problems or a bad starter

9. A test of a starting system reveals that thevoltage drop between the battery positive (+)post and the starter motor terminal "C" is aboutone volt. The most probable cause is:

A. low resistance in the motor circuit

B. high resistance in the motor circuitC. low resistance in the control circuitD. high resistance in the control circuit

10. The voltage drop on the ground side of thestarter motor circuit should be no more than:

A. battery voltageB. 0.1 voltC. 0.2 voltD. 0.5 volt





SELF-TEST ANSWERS

For the preceding self-test on The Starting System,the following best complete the sentence or answer the question. In cases where you may

disagree with the choice - or may simply want toreinforce your understanding - please review theappropriate workbook page or pages noted.

1 . "C" - The starting system has two separateelectrical circuits ... a control circuit and a motor circuit. (Page 1.)

2. "B" - If the transmission is in gear, the controlcircuit between the ignition switch and starter magnetic switch is interrupted by the neutral start

switch. (Page 2.)

3. "B" - Unlike in the conventional starter, themagnetic switch plunger acts directly on the piniongear (not through a drive lever) to push the gear into mesh with the ring gear. (Page 4.)

4. "C" - An over-running clutch disengages thepinion gear and prevents damage to the starter motor when the engine starts. (Page 7.)

5. "A" - If the engine cranks too slow to start, thecause may be a discharged battery, loose or corroded connections, a faulty starter, or engineproblems such as the wrong oil. (Page 8.)

6. "B" - If the starter motor spins, but the enginewill not crank, check the over-running clutch.(Page 8.)

7. "A" - Low current draw, with a low crankingspeed and high cranking voltage, usually indicatesexcessive resistance in the starting circuit. (Page10.)

8. "D" - High current draw, with a low crankingspeed, usually indicates a faulty starter or engineproblems such as the wrong oil or ignition timing.(Page 10.)

9. "B" - With the voltmeter leads connectedbetween the battery (+) terminal and the motor "C"terminal, a reading of more than 0.5 volt indicatesexcessive resistance (in the motor circuit). (Page11.)

10. "C" - With the voltmeter leads connectedbetween the battery (-) terminal and the motor housing, a reading of more than 0.2 volt indicatesexcessive resistance (in the motor ground circuit).(Page 12.)





TOYOTA STARTING SYSTEMS ASSIGNMENT NAME:

1. List the two staring system circuits.

2. List the components that make up the “control circuit”.

3. List the components that make up the “motor circuit”.

4. Explain in detail how a “Conventional Starter” differs from that of a “Gear ReductionStarter”.

5. Explain why an “overrunning clutch” is needed and how it works.

6. Explain how the “starter drive pinion” engages (pushed out) with the ring gear whenthe ignition key is turned to the “Start” position.

7. List and describe the five items included in a “Visual Inspection”.

8. Explain in detail the steps taken in order to perform a “Current Draw Test”.

9. Explain the procedure and the need for a voltage drop test of the “Motor Circuit”



General

The charging system converts mechanical energyinto electrical energy when the engine is running.

This energy is needed to operate the loads in thevehicle's electrical system. When the chargingsystem's output is greater than that needed by thevehicle, it sends current into the battery to maintainthe battery's state of charge. Proper diagnosis of charging system problems requires a thoroughunderstanding of the system components and theiroperation.

Operation

When the engine is running, battery powerenergizes the charging system and engine powerdrives it. The charging system then generateselectricity for the vehicle's electrical systems. Atlow speeds with some electrical loads "on" (e.g.,lights and window defogger), some battery currentmay still be needed. But, at high speeds, thecharging system supplies all the current needed bythe vehicle. Once those needs are taken care of,the charging system then sends current into thebattery to restore its charge.

CHARGING SYSTEMS




Toyota Charging Systems

Typical charging system components include:

IGNITION SWITCH

When the ignition switch is in the ON position,battery current energizes the alternator.

ALTERNATORMechanical energy is transferred from the engineto the alternator by a grooved drive belt on a pulleyarrangement. Through electromagnetic induction,the alternator changes this mechanical energy intoelectrical energy. The alternating currentgenerated is converted into direct current by therectifier, a set of diodes which allow current topass in only one direction.

VOLTAGE REGULATORWithout a regulator, the alternator will alwaysoperate at its highest output. This may damagecertain components and overcharge the battery.

The regulator controls the alternator output toprevent overcharging or undercharging. On oldermodels, this is a separate electromechanicalcomponent which uses a coil and contact points toopen and close the circuit to the alternator. Onmost models today, this is a built-in electronicdevice.

BATTERY The battery supplies current to energize thealternator. During charging, the battery changes

electrical energy from the alternator into chemicalenergy. The battery's active materials are restored. The battery also acts as a "shock absorber" orvoltage stabilizer in the system to prevent damageto sensitive components in the vehicle's electricalsystem.

INDICATOR The charging indicator device most commonly usedon Toyotas is a simple ON/OFF warning lamp. It isnormally off. It lights when the ignition is turned"on" for a check of the lamp circuit. And, it lightswhen the engine is running if the charging system

is undercharging. A voltmeter is used on currentSupra and Celica models to indicate system voltage... it is connected in parallel with the battery. Anammeter in series with the battery was used onolder Toyotas.

FUSINGA fusible link as well as separate fuses are usedto protectcircuits in the charging system.

CHARGING SYSTEMS




Alternator Construction

GENERAL

Two different types of alternators are used on

Toyota vehicles. A conventional alternator andseparate voltage regulator were used on all Toyotas prior to 1979. A new compact, high-speedalternator with a built-in IC regulator

is now used on most models. Both types of alternators are rated according to current output.

Typical ratings range from 40 amps to 80 amps.

CONVENTIONAL ALTERNATOR This type of alternator is currently used on some1986 Tercel models, and all Toyotas prior to 1979.

CHARGING SYSTEMS




TOYOTA COMPACT,HIGH-SPEED ALTERNATOR

Beginning with the 1983 Camry, a compact, high-speed alternator with a built-in IC regulator is used

on Toyota vehicles. Corolla models with the 4A-Cengine use a different alternator with an integral ICregulator.

This new alternator is compact and lightweight. Itprovides better performance, as well as improvedwarning functions. If either the regulator sensor(terminal "S") or the alternator output (terminal "B")become disconnected, the warning lamp goes on.It also provides better serviceability. The rectifier,brush holder, and IC regulator are bolted onto theend frame.

CHARGING SYSTEMS




Al ternator Terminals

Toyota's high-speed alternator has the followingterminals: "B", "IG", "S", "U', and "17".

When the ignition switch is "on," battery current issupplied to the regulator through a wire connectedbetween the switch and terminal "IG". When thealternator is charging, the charging current flowsthrough a large wire connected between terminal"B" and the battery. At the same time, batteryvoltage is monitored for the MIC regulator throughterminal "S". The regulator will increase ordecrease rotor field strength as needed. Theindicator lamp circuit is connected through terminal"U'. If there is no output, the lamp will be lit. Therotor field coil is connected to terminal "P, which is

accessible for testing purposes through a hole inthe alternator end frame.

Regulator

While engine speeds and electrical loads change,the alternator's output must remain even - not toomuch, nor too little.

The regulator controls alternator output byincreasing or decreasing the strength of the rotor'smagnetic field. It does so, by controlling the amountof current from the battery to the rotor's field coil.

The electromechanical regulator does its job with amagnetic coil and set of contact points. The ICregulator does its job with diodes, transistors, andother electronic components.

CHARGING SYSTEMS




Alternator Operation

GENERAL

The operation of the Toyota compact, high-speed

alternator is shown in the following circuitdiagrams.

IGNITION ON, ENGINE STOPPED

CHARGING SYSTEMS




CHARGING SYSTEMS





The charging system requires periodic inspectionand service. Specific problem symptoms, theirpossible cause, and the service required are listed

in the chart below. The service actions require athorough visual inspection. Problems identifiedmust be corrected before proceeding withelectrical tests. These electrical tests include: analternator output test, charging circuitvoltage-drop tests , a voltage regulator (non-IC) test,charging circuit relay (lamp, ignition, engine) tests,and alternator bench tests.

PRECAUTIONS• Make sure battery cables are connected to

correct terminals.

• Always disconnect battery cables (negativefirst!) when the battery is given a quick charge.

• Never operate an alternator on an open circuit(battery cables disconnected).

• Always follow specs for engine speed whengrounding terminal "F to bypass the regulator.High speeds may cause excess output that coulddamage components.

• Never ground alternator output terminal "B." It hasbattery voltage present at all times, even with theengine off.

• Do not perform continuity tests with a high-voltage insulation resistance tester. This type of ohmmeter could damage the alternator diodes.

CHARGING SYSTEMS




VISUAL INSPECTIONA visual inspection should always be your firststep in checking the charging system. A number of problems that would reduce charging performancecan be identified and corrected.

CHECK THE BATTERY• Check for proper electrolyte level and state of charge. When fully charged, specific gravityshould be between 1.25 and 1.27 at 80˚F(26.7˚C).

• Check the battery terminals and cables. Theterminals should be free of corrosion and thecable connections tight.

CHECK THE FUSES AND FUSIBLE LINK• Check the fuses for continuity. These include the

Engine fuse (10A), Charge fuse (7.5A), andIgnition fuse (7.5A).

• Check the fusible link for continuity.

INSPECT THE DRIVE BELT• Check for belt separation, cracks, fraying, or

glazing. If necessary, replace the drive belt.

• Check the drive belt tension using the propertension gauge, Nippondenso BTG-20

Refer to the appropriate repair manual for properdrive belt tension. "New" belts (used less than 5minutes on a running engine) are installed withgreater tension than "used" belts. Tension specsare different for different models.

INSPECT THE ALTERNATOR• Check the wiring and connections. Replace any

damaged wires, tighten any loose connections.

• Check for abnormal noises. Squealing mayindicate drive belt or bearing problems. Defectivediodes can produce a whine or hissing noisebecause of a pulsating magnetic field andvibration.

CHECK THE WARNING LAMP CIRCUIT• With the engine warm and all accessories off,

turn the ignition to ON. The warning lamp shouldlight.

• With the engine started and the ignition in RUN,the warning lamp should be off.

• If the lamp does not operate as specified, checkthe bulb and check the lamp circuit.

CHARGING SYSTEMS




ALTERNATOR OUTPUT TEST

The alternator output test checks the ability of thealternator to deliver its rated output of voltage andcurrent. This test should be performed whenever

an overcharging or undercharging problem issuspected. Output current and voltage shouldmeet the specifications of the alternator. If not, thealternator or regulator (IC or external) may requirereplacement.

A Sun VAT-40 tester, similar testers, or a separatevoltmeter and ammeter can be used. Toyota repairmanuals detail the testing procedures with anammeter and voltmeter. Follow the manufacturer'sinstructions when using special testers, althoughmost are operated similarly. The following stepsoutline a typical procedure for performing thealternator output test using a Sun VAT-40:

CHARGING SYSTEMS




Charging Without Load1. Prepare the tester:

• Rotate the Load Increase control to OFF,

• Check each meter's mechanical zero. Adjust, if

necessary.• Connect the tester Load Leads to the battery

terminals; RED to positive, BLACK to negative.

• Set Volt Selector to INT 18V.

•Set Test Selector to #2 CHARGING.

• Adjust ammeter to read ZERO using the electricalZero Adjust control.

• Connect the clamp-on Amps Pickup around thebattery ground (-) cables.

2. Turn the ignition switch to "ON" (engine notrunning) and read the amount of discharge onthe ammeter. This is a base reading for currentthe alternator must supply for ignition andaccessories before it can provide current tocharge the battery.

NOTE: The reading should be about six amps.

3. Start the engine and adjust the speed to about2000 rpm. Some models may require a differentspeed setting.

4. After about 3-4 minutes, read the ammeter and

voltmeter. Add this ammeter reading and thereading found in step 2 (engine not running).

NOTE: The total current should be less than 10amps. If it is more, the alternator may still becharging the battery. Once the battery is full y

charged, you should get specified results.

The voltage should be within the specs for thealternator. This is usually between 13 and 15 volts.Refer to the appropriate repair manual. If thevoltage is more than specified, replace theregulator. If the voltage is less than specified,ground the alternator field terminal "F" and checkthe voltmeter reading. This bypasses the regulator,so do not exceed the specified test speed. If thereading is still less than specified, check thealternator.

5. Remove ground from terminal "F."

Charging With Load6. With the engine running at specified speed,

adjust the Load Increase control to obtain thehighest ammeter reading possible withoutcausing the voltage to drop lower than 12 volts.

7. Read the ammeter.

NOTE: The reading should be within 10% of thealternator's rated output. If it is less, the alternator

requires further testing or replacement.

CHARGING SYSTEMS




CHARGING SYSTEMS




VOLTAGE-DROP TESTSVoltage-drop testing can detect excessiveresistance in the charging system. These testsdetermine the voltage drop in the alternator outputcircuit. Both sides of the circuit should be checked

... insulated side as well as ground side.Excessive voltage drop caused by high resistancein either of these circuits will reduce the availablecharging current. Under heavy electrical loads, thebattery will discharge.

A Sun VAT-40 tester or a separate voltmeter canbe used. The following steps outline a typicalprocedure for performing voltage-drop tests usinga voltmeter:

Output Circui t - Insulated Side

1. Connect the voltmeter positive lead to thealternator's output terminal "B" and thevoltmeter's negative lead to the battery'spositive (+) terminal.

2. Start the engine and adjust the speed toapproximately 2000 rpm.

3. Read the voltmeter. The voltage drop should beless than 0.2 volt. If it is more, locate and correctthe cause of the high resistance.

Output Circuit - Ground Side

1. Connect the voltmeter's negative lead to thealternator's frame and the voltmeter's positivelead to the battery's negative (-) terminal.

2. Start the engine and run at specified speed(about 2000 rpm).

3. Read the voltmeter. The voltage drop should be0.2 volt or less. If it is more, locate and correct

the cause of high resistance. Excessiveresistance is most likely caused by loose orcorroded connections.

CHARGING SYSTEMS




CHARGING CIRCUIT RELAY TESTS

Various charging system layouts are used on Toyota vehicles. The indicator lamp circuit may ormay not be controlled by a relay. Depending on the

model, when a relay is used, it may be a separatelamp relay, the ignition main relay, or the enginemain relay. Each is checked using an ohmmeter.

Charge Lamp Relay

When used, the charge lamp relay is located onthe right cowl side of the vehicle. The followingsteps are used to check this relay:

1. Check relay continuity.

• Connect the ohmmeter positive (+) lead to

terminal "4," the negative (-) lead to terminal "3."Continuity (no resistance) should be indicated.

• Reverse the polarity of the ohmmeter leads. Nocontinuity (infinite resistance) should be indicated.

• Connect the ohmmeter leads between terminals 1and "2." No continuity (infinite resistance) shouldbe indicated.

If the relay continuity is not as specified, replacethe relay.

2. Check relay operation.

• Apply battery voltage across terminals "3" and"4."

NOTE: Make sure polarity is as shown.

• Connect the ohmmeter leads between terminals

“1” and "2." Continuity (no resistance) should beindicated.

If relay operation is not as specified, replace therelay.

CHARGING SYSTEMS




Ignition Main Relay

The ignition main relay is located in the relay boxunder the instrument panel. The following stepsare used to check this relay:

1. Check relay continuity.

• Connect the ohmmeter leads between terminals“1” and "3." Continuity (no resistance) should beindicated.

• Connect the ohmmeter leads between terminals"2" and "4." No continuity (infinite resistance)should be indicated.

If relay continuity is not as specified, replace therelay.

2. Check relay operation.

• Apply battery voltage across terminals "l " and"3."

• Connect the ohmmeter leads between terminals"2" and 'A." Continuity (no resistance) should beindicated.

If relay operation is not as specified, replace therelay.

CHARGING SYSTEMS




ALTERNATOR BENCH TESTS

If the on-vehicle checks have indicated that thealternator is defective, it should be removed forbench testing and replacement. Specific

procedures for removal, disassembly, inspection,and assembly are noted in the appropriate repairmanuals. Only the electrical bench tests arecovered here.

• Always disconnect the battery ground (-) cablebefore removing the alternator.

• Refer to the appropriate repair manual for testspecifications.

An ohmmeter is used for electrical bench tests onthe rotor, stator, and diode rectifier. The following

steps are typical:

Rotor Tests

• Check the rotor for an open circuit by measuringfor resistance between the slip rings. Someresistance (less than 5 ohms) indicatescontinuity. If there is no continuity (infiniteresistance), replace the rotor.

• Check the rotor for grounded circuits bymeasuring for resistance between the rotor andslip ring. Any amount of resistance indicates a

ground (continuity). The resistance should beinfinite ( 0 ohms ). If not, replace the rotor.

CHARGING SYSTEMS




Diode Tests

Diodes can be checked with the alternator on thevehicle using a scope. Scope testing can identifyopen or shorted diodes, as well as problems in the

stator coils. The scope patterns shown below include:

a) Normal alternator output;

b) one diode short-circuited;

c) two diodes of the same polarity short-circuited;

d) one diode open;

e) two diodes open;

f) one phase of the stator coil short-circuited;

g) one phase of the stator coil disconnected; and,

h) two phases of the stator coil short-circuited.

CHARGING SYSTEMS




CHARGING SYSTEMS




This brief self-test will help you measure yourunderstanding of The Charging System. The styleis the same as that used for A.S.E. certificationtests. Each incomplete statement or question isfollowed by four suggested completions oranswers. In each case, select the one that bestcompletes the sentence or answers the question.

1. A regulator controls alternator output voltage byregulating:

A. sine-wave voltageB. battery voltageC. field currentD. output current

2. In an alternator, alternating current is convertedto direct current by the:

A. statorB. brushesC. rectifierD. regulator

3. If the charging system indicator lamp goes onwith the engine running, the cause may be lossof voltage at terminal:

A. "IG"B. "S"C. "L"

D. "F

4. With the engine not running and the ignition ON,the charge lamp should light. If it doesn't, thismay indicate a:

A. burned out bulbB. grounded bulbC. loose drive beltD. overcharged battery

5. Which alternator terminal can be grounded fortest purposes?

A. "B"B. "IG"C. “S"D. "F

6. When performing a visual inspection of thecharging system, the alternator drive belt shouldbe checked for proper tension.

Technician "A" says that new-belt tensionspecs are higher than those for used belts.

Technician "B" says that the belt tension isdifferent for different Toyota models.

Who is right?

A. Only AB. Only BC. Both A and BD. Neither A nor B

7. The amount of current the alternator must supply

or ignition and accessories is about:

A. four ampsB. six ampsC. eight ampsD. ten amps

8. In an alternator output test under load, the outputshould be:

A. about 10 ampsB. about 30 ampsC. within 10% of rated output

D. within 20% of rated output

9. To check for excessive voltage drop on theinsulated side of the alternator's output circuit,you would connect a voltmeter between the:

A. battery terminal and ignition switchB. battery terminal and groundC. battery terminal and alternator "S" terminalD. battery terminal and alternator "B" terminal

10. High resistance in an alternator output circuit isoften caused by:

A. a discharged batteryB. a shorted diodeC. loose or corroded connectionsD. a bad regulator

CHARGING SYSTEMS




SELF-TEST ANSWERS

For the preceding self-test on The ChargingSystem , the following best complete thesentence or answer the question. In cases where

you may disagree with the choice - or may simplywant to reinforce your understanding - pleasereview the appropriate workbook page or pagesnoted.

1 . "C" - The regulator controls alternator output byincreasing or decreasing the amount of currentfrom the battery to the rotor field coil. (Page 5.)

2. "C" - The alternating current is changed intodirect current by the rectifier, a set of diodeswhich allow current to pass in only onedirection. (Page 2.)

3. "B" - If either the regulator sensor (terminal "S")or the alternator output (terminal "B") becomedisconnected, the warning lamp goes on. (Page4.)

4. "A" - If the warning lamp does not light, with theignition ON and the engine not running, thepossible causes include a blown fuse, burnedout lamp, loose connections, or faulty relay orregulator. (Page 9.)

5. "D" - Terminal "F is the only terminal that can be

grounded. Never ground alternator outputterminal "B. It has battery voltage present at alltimes, even with the engine off. (Page 9.)

6. "C" - A "new belt" is one that has been used forless than 5 minutes. It is installed with moretension than a used belt, because it will stretchsome during use. Methods of checking aredifferent for different models. (Page 10.)

7. "B" -The reading should be about six amps. Thisis the amount of current the alternator must

supply for ignition and accessories. (Page 12.)

8. "C" - With the alternator operating at maximumoutput, the reading should be within 10% of rated output. (Page 12.)

9. "ID" - To check for the insulated circuit voltagedrop, connect the voltmeter leads to thebattery's (+) terminal and the alternator output(B) terminal. (Page 14.)

10. "C" - Excessive resistance is most likelycaused by loose or corroded connections.

(Page 14.)

CHARGING SYSTEMS


Taken with permission from the

Toyota Basic Electrical Course#622,



USING THE ELECTRICAL WIRING DIAGRAM

USING TOYOTA WIRING DIAGRAMS




ELECTRICAL DIAGNOSTIC TOOLS

Page 1 ' Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.



DIAGNOSING BODY ELECTRICAL PROBLEMS




SEMICONDUCTORS

One of the ba sic building blocks of all

modern electronic devices is t hesemicondu ctor . Semicondu ctors ca ncondu ct or block electr ical curr ent .B eca use of this a bili ty , semiconductorsserve a n importa nt funct ion in everyt hingfrom r ela ys t o the integra ted circuits ofcomputers.

This chapt er exa mines diodes a s w ell a ssome of th e oth er components us ed toconst ruct electronic devices, such a scapacitors a nd r esistors. Diodes allow

current to f low thr ough t hem in only onedirect ion an d a re used in a var iety ofw a ys, including suppression of volta gespikes ("de-spiking") and convertinga lterna t ing current to direct current inan a l t e rna tor.

Ca pacitors store electr ica l cha rges an da re used for electrical noise a nd volta gespike suppression. Ca pacitors ar e alsoused in t imer circuits t o delay turn ing onor off a device or syst em.

This cha pter w ill exam ine each of thefol low ing a reas :

Capaci tors

Cur r en t F l ow Th eor y

Semi cond uctor T heor y

Diodes

CAPACITORS

Ca pacitors ha ve th e a bility to absorb a nd

store an electr ica l cha rge and t henrelea se i t into th e circuit . Ca pacitors a refrequently used in t imers wh ich w ill keepa circuit or device in opera tion for aperiod of t ime a fter t he circuit ha s beenshu t off. An exa mple of th is is a d omelight circuit t ha t st a ys on for a specifiedlength of t ime a fter th e door ha s beenclosed.

A capacitor is const ructed from tw oconducting pla tes sepa ra ted by a n

insula t ing ma ter ia l ca l led a dielect r ic .This insula t ing ma ter ia l can be pa per ,p las t ic, f i lm mica , g lass , ceram ic, a ir ora va cuum. The pla tes can be a luminumdiscs, a luminum foil or a th in f i lm ofmet a l a pplied t o opposite sides of a soliddielectr ic. These lay ered ma teria ls a reeither rolled into a cylinder or left fla t .

The opera tion of a capa citor is relat ivelysimple. When t he capa citor is pla ced in acircuit , a charge builds on t he pla tes unt il

the plat es a re at t he same potent ia l a s thepow er source. When th e source poten tia lis removed, th e ca pacitor will dischar gea nd cause a current to f low in th e circuit .I f t he potent ia l of the source cha nges, thecapa citor will eith er cha rge or dischar geto ma tch t he source, thereby smooth ingvoltage fluctuations in the circuit .

SEMICONDUCTORS




Since current ca n f low int o a capa citoronly until the cha rge reaches th epotent ia l of th e source, a capa citor w illblock curr ent in a DC circuit . ACcurrents a re not blocked by a ca pacitorbeca use th e pola rity of the AC circuit iscont inual ly changing .

The unit of mea sure of ca pacita nce is th e" f a r a d . " Mos t c apac ito r s a re much lesstha n one fara d, and a re ra ted in micro-fa ra ds or picofa ra ds. When capa citorsa re connected in series th eir tota lcapa cita nce is reduced, l ike resistorsconn ected in pa ra llel . When ca pacitors

a re connected in pa ra llel their tota lcapacita nce increases, l ike tota lresista nce w hen resistors a re connectedin series.

There a re th ree types of ca pacitors:cera mic for electr onic circuits , pa per a ndfoil for noise suppression in cha rging a ndignit ion sy stems, a nd electrolyt ic as usedin tu rn s igna l f l a shers. Ordina ry a ndelectrolyt ic ca pacitors a re designa ted bydi f ferent symbols in w ir ing diagra ms.

As sta ted, ca pacitors ha ve three uses:

Noise su pp ression —Noise in an a udiosyst em is often ca used by AC electr ica lvolta ge riding on t op of the D C voltagesupplying pow er to a ra dio or ta pe player.A capa citor conn ected t o the circuit w illfilter out th e AC volta ge by allow ing it t o

pass t o ground. Most a lterna tors onToyota vehicles ha ve a capacitor built infor th is purpose.

Spike sup pr ession —A capa citor cana bsorb volta ge spikes in a circuit . Thisa pplica t ion ha s been used in convent iona lignit ion syst ems to prevent a n a rc fromjumping the breaker points w hen th eya re opened.

Timers—A resistor put in s eries w ith a

capa citor can keep current f low ing in acircuit for a specified am ount of t imea fter pow er from the source ha s beenremoved. This ca n be used t o keep domelights on a fter th e vehicle doors a reclosed. The resistor-capacitor or RCcircuit in t he example above is used t okeep a tra nsistor turned on, so thet ra nsis tor a l low s current to remainflowing to the syst em.

SEMICONDUCTORS




CURRENT FLOW THEORY

B efore w e discuss semiconductors a nd

how t hey opera te , i t is importa nt tounderst a nd current f low th eory. Therea re tw o different theories of how currentflow s: electron current f low a ndconvent iona l current f low (sometimesreferred t o as " hole f low " ).

The electr on current flow t heory sa ys th a tcurrent f low in a circuit is t he movementof electrons through the conductors.Since the electrons ha ve a negat ivecha rge and unl ike cha rges a t t ra ct each

other, th e electr ons move from th enegat ive termina l of the ba tt ery to thepositive termin a l. So th e electr on t heorysa ys tha t current f lows from nega t ive topositive.

The convent ional curren t flow t heory,wh ich h a s been a ccepted for ma ny y ears ,sa ys th a t current f low s from t he posit iveterminal of the bat t ery to the negat ivetermin a l . The convent iona l current f low th eory is sometimes called t he hole flow

theory beca use this theory sa ys tha t w hena n electr on moves, a n empt y h ole is left

behind. The holes a re sa id to tra vel in t heopposite direction from the electrons inth e conductor . To understa nd h ow th iscould w ork thin k of a line of ca rs st oppeda t a stop sign. As one ca r pulls a w a y fromth e stop sign a hole is left a nd t he next ca rin line moves forw a rd t o fill th e hole. Now th e hole ha s moved back to where th esecond car w as an d th e third car movesforw a rd t o f i l l i t . As each car in t urnmoves forw a rd t o fill the hole, the holemoves to the rea r. The car s move onedirection a nd t he holes move the oth er,just like electr ons a nd h oles in a circuit .

When looking a t a n electr ical circuit ,either t he electron current flow t heory orconventional current f low theory can bea pplied because th e circuit opera tion a ndth e schema tic will be the sa me. Whendeal ing wi th dia gra ms tha t use elect ronicsymbols , such a s diodes an d t r a nsis tors ,th e a rrow in the symbol a lw a ys points inth e direction of conventiona l curr ent flow.B eca use th e conventional current f low th eory is w idely accepted in t hea utomotive industry, i t is used

th roughout th is book.

SEMICONDUCTORS




BASIC THEORY OF

SEMICONDUCTOR OPERATION

Semiconductors are importa nt t oundersta nd beca use they pla y such aprominent par t in a utomotive electr onics.You will deal wit h th em nearly everytime y ou diagn ose a Toyota electronicsystem.

Some ma teria ls conduct electr ica lcurrent bett er tha n others. This is due toth e number of electr ons in th e outerm ostring , or sh ell, of electrons of the a tomsth a t ma ke up the ma terials . The outer

shell is ca lled the va lence shell" or" r ing . " I f th e va lence r ing has f ive toeight electrons, i t ta kes a large a mount offorce to caus e one of th e electrons t o breakfree from the a tom, ma king tha t ma ter ia la poor conductor . Such ma teria ls ar eoften used as insu la tors to block current .ma ter ia ls tha t a re ma de up of a toms wi thone to thr ee electr ons in t heir va lencering a re good conductors beca use a sm a llforce will cause t he electrons to brea kfree. Semiconductors fa l l somew here in

th e middle. Since th ey ha ve four electr onsin t heir valence r ings, th ey a re not goodinsula tors or conductors.

Semiconductors ar e usual ly m a de fromgerma nium or s i l icon wh ich, in t he irna tura l s t a tes , a re pure crysta ls . Neitherha ve enough free electr ons to supportsignif ica nt current f low, but by a ddinga toms from other ma ter ia ls—a processcalled doping— the crystals will conductelectr icity in a wa y th at is useful inelectr onic circuit s. The s emiconductorma teria l, aft er it ha s been doped, becomeseither N-ty pe ma teria l or P -ty pe ma teria l.

SEMICONDUCTORS




Silicon is the most comm only usedsemiconductor m a teria l . The outer sh ellof a si l icon a tom cont a ins four electrons,but it n eeds eight t o be sta ble. Therefore,the a toms link together to sha reelectrons. In this sta te , si l icon w ill notconduct current .

When sil icon is doped w ith a ma teria lsuch as phosphorous, which ha s f ive

elect rons , the resul tan t ma ter ia l conta insfree e lect rons—known a s ca rr iers—a ndtherefore conducts electricity. Thiscreat es N-type ma terial , na med for i tsnega tive char ge ca used by t he excess ofelectrons.

Sil icon can a lso be doped w ith a ma terialtha t ha s fewer th a n four electrons in i tsouter shells , as is th e ca se with boron an dits t hree electrons. The resulta nts t ructure has "h oles " lef t by t he missing

electrons. As discussed ea rlier , a nelectron can move into these holes an d, ineffect, t he h ole moves in t he oppositedirection. The a bund a nce of holes crea tesP -ty pe ma teria l, na med for its positivecha rge due t he la ck of electr ons or excessof holes. B y joining t his N-ty pe and P -ty pema ter ia l , d iodes and t ra nsis tors can beformed.

DIODES

Diodes block current flow in one directiona nd pa ss current in th e oppositedirection. This is a ccomplished by joinin ga layer of P t ype ma terial and a layer of N-type ma te r ia l dur ing ma nufac tur ing .Where they m eet is ca lled t he P Njunction. At th e P N junction, some of theelectrons of the N-type ma teria l move int osome of th e holes in the P -ty pe ma teria la nd crea te a neutra l a rea a t t he junct ion.Another wa y of thinking of this is tha t t he

positive holes a tt ra ct t he negat iveelectrons lea ving n o free electrons, socurrent is una ble to f low past tha t point .This neutra l a rea a cts a s a ba rr ier ,w hich is ca lled the depletion region.

SEMICONDUCTORS




The depletion region is very t hin a ndresponds r a pidly t o volta ge cha nges. I t ishere tha t current is either a llow ed to pa ssor is blocked.

When t he diode is conn ected in a circuitw here the N-ty pe ma teria l is connected t othe negat ive terminal of the bat tery an dth e P -type ma teria l is connected to th epositive t ermina l, the excess electrons inth e N-type ma terial a re repelled by thenegat ive potentia l of the ba tt ery. At t hesa me time, the positively cha rged holes inth e P-type ma terial a re repelled by th epositive potentia l of the ba tt ery, resultingin a concentra t ion of holes a nd electronsa t t he depletion region. When volta gea pplied to the diode is great enough (.5 to.7 volts) electr ons in th e N ty pe mat erialw ill move a cross t he depletion

region at th e junction, filling holes in theP -type mat erial an d lea ving holes in th eN-type ma terial . Electrons move throughth e diode to the positive term ina l of theba tt ery an d holes move th rough the diodeto the nega tive terminal of the batt ery.When t his ha ppens t he diode condu ctscurrent a nd is said t o be forw a rd biased.

If t he conn ection of the d iode in t hecircuit is reversed, wit h t he N-ty pema teria l connected t o the positiveterminal of the bat tery a nd th e P-typema terial connected t o the negat iveterm ina l, the diode is reverse

biased. In t his case, the electrons in t heN-type material a re at t racted to thepositive termina l of the batt ery an d theholes in t he P -type mat erial a re at tra ctedto the nega tive terminal of the batt ery.This results in a n increase in thedepletion region or neutr a l zone so nocurrent can f low t hrough t he diode.Whet her t he diode cond ucts or blockscurrent flow is determin ed by the volta gepolarity applied to it.

SEMICONDUCTORS




If t he reverse bias volta ge applied t o adiode is great enough, th e volta ge ca novercome th e depletion r egion a t th ejunction a nd t he diode will conduct for ashort period before burn ing open. Whenth is ha ppens t he diode is destr oyed.

The th ree ma in uses for diodes in t hea ut omobile a re rectifica tion, de-spiking,and isolat ion.

Rectification —Sin ce a diode will a llow

current t o flow in one direction a nd n otth e oth er, it can be used to turna l terna t ing current int o direct current .This is called rectificat ion. Diodes canprovide either full-w a ve or ha lf-w a verectifica tion, depending on th e number ofdiodes a nd h ow th ey a re connected.

A ha lf-w a ve rectifier consist ing of onediode will have a n output voltage th a t isa pproxima tely one ha lf of th e AC source.

Since the output from a n AC pow ersource continually changes or a lternatesfrom posit ive to negat ive, the diode isforw a rd biased for part of the output a ndreverse bia sed for th e oth er. The diodew ill a l low current to f low in t he circuitw hen it is forwa rd biased but w ill blockth e flow of current w hen it is reverse

biased. The result is th a t only ha lf of thew a ve is output w hile the other ha lf isblocked by t he diode. This ty pe of rectifieris not commonly found in a n a utomotivea pplica tion since it is not a n efficient w a yto rectify AC t o DC to cha rge a ba tt ery.

A full-w a ve rectifier uses a four-diodenetw ork to rectify both h a lves of a n ACoutput . In such a system, current f lowsfrom the first h a lf of the pha se of th e ACpow er source thr ough th e first diode inforw ar d b ias , through the externa lcircuit , through the second diode, thencompletes th e circuit . On t he second h a lfof th e phase, the current f lows t hroughth e third diode, through th e externa l

circuit , through t he fourt h diode a ndcompletes t he circuit .

SEMICONDUCTORS




B y using four diodes in the full-w a verectifier, all of the current flow s to th e DCpart of the circuit a nd t he current in t heDC par t a lw a ys f lows the sam e direct ioneven t hough th e current f low in t he ACpow er source cha nges dir ect ions.

The fu ll-w a ve, t hr ee-pha se rectifier foundin an a utomotive alterna tor goes a stepfur ther . Because t he a l terna tor usesth ree coils th a t produce th ree overlappingAC sine w a ves sta ggered at 120 degreeinterva ls, six diodes ar e required t oa chieve full-w a ve rectificat ion. Ea ch coiluses four of th e diodes to rectify t he

output, achieving full-wave rectification(a s in t he full-w a ve, single-pha se rectifierdiscussed ea rlier). B eca use th e coils a nddiodes a re interconnected, the sa mediodes a re used by different coils a tdifferent t imes. Due to th e overlap of thew a ves, output from each coil in this t ypeof a lterna tor produces a sm ooth output t othe DC system.

The follow ing w orksheet shows how t hesix diodes can r ectify t he output of all

th ree coils.

SEMICONDUCTORS




DIODE RECTIFICATION WORKSHEET

In ea ch of the i l lustra t ions above, t ra cethe pat h of current f low t hrough thestator coils, the corresponding diodes andth e DC circuit .

The ar rows in t he i l lustra t ions next t o thesta tor coils show t he direction ofconvent iona l current f low.

SEMICONDUCTORS




De-spiking—Diodes a re used on somerelay coils to suppress volta ge spikes.These spikes ca n d a ma ge componentssuch as t ra nsist ors in the cont rol circuitof the r elay . The volta ge spike is producedby t he collapsing ma gnetic f ield in therela y coil wh ich occurs w henever currentflow th rough t he coil is stopped suddenly .The volta ge induced in t he rela y coil issimilar t o the w a y a n ignit ion coilopera tes. The induced volta ge in a relaycoil ca n be severa l t imes more tha n t hesystem voltage.

A de-spikin g diode is conn ected in

para llel wit h t he relay coil . I t is reversebiased wh en the rela y is turned on,th erefore no curr ent

w ill flow t hr ough the diode. When th erela y cont rol circuit is opened, curren tstops f low ing t hrough t he coil , ca using

th e ma gnetic field to collapse. Thema gnetic l ines of force cut th rough th ecoil an d induce a volta ge. Sin ce th ecircuit is open, n o curr ent flows. Thevolta ge builds unt il it reaches about .7volts, enough to forw a rd bia s th e diode,completing t he circuit to th e oth er end ofth e coil. The curr ent flows a round in t hediode a nd coil circuit unt il the volta ge isdissipated.

B eca use some relays a re located in veryhot environment s w here de-spikingdiodes ca n fa il premat urely, resistors ar esometimes used instead. The resistor ismore dura ble a nd can suppress volta gespikes in much the sa me wa y a s thediode, but t he resistor will a l low currentto f low thr ough it w henever the relay ison. Therefore resista nce of t he r esistormus t be fa irly h igh (400 to 600 ohm s) toprevent t oo much current f low in t hecircuit . B eca use of resistors' highresista nce, th ey are not quit e as efficienta t suppressing a volta ge spike as diodes.

SEMICONDUCTORS

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Isolation—A diode can be used t osepa ra te t w o circuits . Diodes are used inth is wa y on ma ny Toyota models. TheE lectr onic Load Sense (ELS ) circuit usedon a Ca mry is a good exam ple. Thissystem signals th e EC U t o increase theidle speed w hen certa in electr ical loa dsa re turned on. I t uses tw o diodes so tw odifferent circuits can provide a volta gesigna l to the same terminal on the EC U.Without diodes, w henever either of th esystems w ere turned on, volta ge woulda lso be applied to th e oth er circuitcausing it t o operat e.

SEMICONDUCTORS




Zener d iode—A zener diode a cts like a nordinar y sil icon diode w hen in th eforw ar d bias direct ion, but i t ha s beenspecia lly doped t o a ct very different ly inreverse bia s. A zener diode allowscurrent to flow in r everse bias a t aspecif ic volta ge with out da ma ge over a ndover a ga in. The reverse bias volta ge atw hich th e zener w ill conduct , sometimescalled th e zener point , differs from onezener t o an other a s each zener diode isdoped to ha ve a zener point a t a specificvoltage.

A zener d iode can be used to suppressspikes by connecting it betw een th e circuita nd ground w ith t he diode reverse biased.When a volta ge spike exceeds th e zenerpoint of the diode, it completes t he circuitto ground a nd prevents t he spike fromda m a g i ng a ny t h i ng .

A more comm on use of a zener d iode ina n a utomobile is to sense th e cha rgingsyst em volta ge. B y conn ecting t he zener

betw een th e base of a t ra nsistor a nd th epositive side of the cha rging sy stem, th ezener can a llow current t o flow to the ba seof the tr a nsistor wh en its zener point isrea ched. If th e zener point is 14.5 voltsa nd th e tra nsistor to w hich th e zener isconnected turns off alternator fieldcurrent w hen the t ra nsis tor is turned on,a consta nt cha rg ing system vol ta ge canbe maint a ined. As soon a s the syst emvolta ge drops below th e zener point , th ediode stops conduct ing a nd t he tra nsistor

tur ns off , a l low ing f ield current to f low .

SEMICONDUCTORS




Light emitting diodes (LEDs)—An L ED isa diode tha t is specially designed toproduce l ight . LE Ds a re made w i th atra nsparent epoxy case so they can emitth e light t hey produce wh en forw a rdbia sed. The color of t he light given off bya n LE D can be red, green or infra red,depending on how t he ma terial is d opedAn LE D, l ike a sta nda rd sil icon diode,w ill conduct current in only onedirection. The forw a rd bia s volta ge dropof an LE D (1.5 to 2 volts) is much h igherth a n a si l icon diode. The forw a rd bia scurrent through a n LED must becontrolled, as w ith a ny other

semiconductor ' or da ma ge w i l l resul t .LED s ha ve advanta ges over ordinarybulbs, su ch a s longer life, cooleroperat ion, lower volta ge requirementsa nd t he abil ity to produce the sam ea mount of l ight a s an incan descent bulbwhile consuming less power.

In vehicles, LED s a re used in a var iety ofw a ys , including displa ys a nd indica tors .LE Ds a re also used in conjunct ion wit hphototra nsistors, wh ich convert l ight toelectr ical curr ent . A vehicle speedsensor, know n a s a photo-coupler orlight-a ct iva ted sw itch, is a good exam ple.In a speed sensor, th e speedometer ca bleis connected t o a slotted w heel whichsepa ra tes the LED from thephototra nsistor . As th e wheel turns, i tconst a nt ly breaks th e beam of lightemitted from th e LED t o thephototra nsistor , thereby turning t hephototra nsist or on a nd off. The pulsed

signa l goes to the computer an d is used todeterm ine vehicle speed.

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SEMICONDUCTORS




SEMICONDUCTORS

ASSIGNMENT NAME:

1. Descr ibe the cons t ruct ion and opera t ion of a capaci tor.

2. N a me t h e t h ree t y pes of ca pa cit or s.

3. D es cr ibe t he t h r ee u ses of ca p a cit or s.

4. N a m e a nd expla i n bot h cu rr en t flow t heor ies .

5. Descr ibe how a semicondor dif fers from a conductor or an insula tor.

6. Wha t a re two common t ypes of semiconductor ma ter ia l .

7. Expla in what “Doping “ is and how N-Type or P-Type mater ia l is made .

8. Descr ibe the funct ion and cons t ruct ion of a “D iode” .

9. E xpla in th e t er m P N jun ct ion .

10. Descr ibe the deplet ion region of a diode.

11. Wha t is the voltage drop (the voltmeter reading) of a diode?

12. Expla in the t erms “Forward” and “Reverse” B ia s .

13. Descr ibe Rect i fica t ion and how diodes are used.

14. Explain the dif ference betw een half-wa ve an d full-wa ve rect if icat ion.

15. Describe th e function of a D e-spiking (Volta ge Suppression) diode.

16. Explain the operat ion of a De-spiking (Voltage Suppression) diode.

17. Descr ibe the funct ion of an I sola t ion diode.

18. Expla in the opera t ion of an I sola t ion d iode.

19. Expla in how a “Zener Diode” dif fers f rom a convent iona l diode.

20. Expla in the term “Zener P oint ” (Avalanche Point) and w hat happens a t this point .

21. Expla in how a “Light Emit t ing Diode” (LED) di ffers f rom a convent iona l diode.

22. What is the vol tage drop (the vol tmeter reading) of an LED?



THE BIPOLAR TRANSISTOR

TRANSISTORS

A tra nsis tor can be used a s a n a mplif ierto cont rol electric motor speed such a s ACblow er motors, or a s solid sta te sw itchesto cont rol actua tors such a s fuel injectors.

This cha pter w ill cover ea ch of thefol lowing four a reas :

Tr an sistor Oper at i on

Tr ansistor App l i ca t i ons

Tr ansistor Gain

In tegra t ed C i rcu i t s

Tra nsis tors are ma de from t he sam e N-type and P -type mat eria ls as diodes andemploy t he sa me principles. Tra nsist ors,however, ha ve two P N junct ions instea dof just one like a diode ha s. The tw o PNjunct ions a llow a tra nsist or t o perform m ore funct ionst h a na diode , such a s ac t ing as a swi tch or a nampli f ier .

The bipola r tr a nsist or is ma de up of th reepart s: the emit ter , the base and t hecollector. There a re t w o types of bipola rt r ans is tor s : the P NP and t he NPN. In theP NP t ra nsis tor th e emit ter is made from

P -type ma terial, t he base is N-typema teria l an d th e collector is P-ty pema ter ia l . For the P N t ra nsis tor tooperat e, the emitter m ust be connected t opositive, th e base to nega tive and thecollector t o nega tive.

The NPN t r an sis tor ha s an emit ter ma defrom N-ty pe ma teria l. I ts ba se is P -ty pema teria l an d th e collector is N-ty pema ter ia l . For the NP N t ra nsis tor tooperat e, the emitter m ust be connected t o

negat ive, the base to positive and t hecollector t o posit ive Aside from th e wa y inwhich the NPN and P NP t r ans is tor s a reconn ected in t he circa t hey opera te th esame wa y . Bo th t r a ns is tor ha ve a forwa rdbiased junct ion a nd a reverse biasedjunct ion, a nd t hree pa rts-the emit t er , theba se a nd t he collector-formed in a th ree-layer a r r a ngement

TRANSISTORS




Current f low betw een th e emit ter a nd

ba se controls the current flow betw een th eemitt er a nd collector. The emitt er of thetr a nsist or is th e most h eavily doped so itha s th e most excess electrons or holes,depending on w hether th e emit t er is P-ty pe or N -ty pe ma ter ia l. The collector isdoped slight ly less tha n t he emit ter a ndth e base is very th in wit h th e fewestdoping a toms. As a result of this t ype ofdoping, the current f low in t he emit ter-collector is much grea ter th a n in th eemit ter-base. B y regulat ing the current a t

th e emit ter-ba se junction, the a mount ofcurrent a l low ed to pa ss from the emit terto t he collector ca n be contr olled.

The symbols for both P NP a nd NP Ntra nsis tors a re very s imila r . Thedis t inguishing fea ture is the arr ow ,w hich is a lw a ys loca ted in the emit tera nd a lwa ys points in t he direct ion ofconvent iona l curr ent flow . The ba se ispar t of th e symbol wh ich looks like a " T"a nd t he rema ining l ine, opposite the

emitt er, is th e collector. In th e symbol fora P NP t ra nsis tor the arrow in the emit terpoints t ow a rd t he center so the currentflow is from emit ter t o ba se an d fromemitter to collector . In t he NP N t ra nsistorthe a rrow

in the emit t er points a w a y from th ecent er so th e current flow is from the bas eto emitter a nd fr om the collector t oemit ter .

One of the m ost comm on uses of at ra nsis tor in a n a utomobile is as aswitch. Sw itching t ra nsis tors ca n befound in solid st a te contr ol modules a ndcomputers. They control devices on thecar such a s th e fuel injector in a n E FI caror a mecha nica l re lay t ha t opera tes there t rac t motor on a car wi th re t rac tab leheadl ights . When an NP N t ra nsis tor is

used as a switch, the emit ter of thetra nsistor is grounded a nd th e ba se isconn ected t o positive. If th e volta ge isremoved from t he ba se, no current f low sfrom the emitt er to the collector a nd t hetra nsistor is off . When th e base is forw a rdbiased by a large enough volta ge, currentw ill flow from th e emitter t o the collector.Essentia lly, the tra nsistor is being used tocontr ol a la r ge current w i th a sma l lcurrent l ike a s ta r ter re lay . A smal la mount of current t o the relay w ill

complete a circuit so a la rge current canflow.

TRANSISTORS




TRANSISTOR GAIN

We know t ha t t he current flow betweenthe emit t er an d ba se contr ols th e currentflow betw een t he emitt er a nd collector.Also, th e am ount of curr ent flow betw eenthe emit ter and ba se will a f fect t hea mount of emit ter collector curr ent. Thera t io between these tw o currents isknown as the " ga in " o f the t r ans is tor .This gain a llows us t o use a tr a nsistor tocontrol a la rge current w i th a very sma l l

current s imilar t o the wa y a re la yopera tes . Exam ple show n: i f a t ra nsis torha d a ga in of 100 and t he emitt er-basecurrent w a s increa sed by 10 milliam ps or.01 a mps, t he emitt er collector currentw ould increase by 100 times or 1 a mp.This t ype of increas e will occur unt il th et ra nsis tor rea ched sa tura t ion. This is th epoint w here increasing th e emit t er-basecurrent does not increase t he emit ter-collector curr ent . Tra nsis tors u sed forswitching usua l ly opera te a t the

sa t ura t ion point w hen turned on, wh i let ra nsis tors th a t a r e used for a mpli f iersopera te in t he ra nge betw een off andsa tura t ion .

Another a pplica t ion for a t ra nsistor isa mplifica t ion. This situa t ion ta kesa dvan ta ge of the relat ionship betw een t heemit ter base current a nd th e emit ter-collector current . Since a sm a ll cha nge incurrent f lowing through th e t ra nsis torfrom t he emit t er to the base has aproportionally la rger effect on t heemitter-collector current, we can usetra nsistors to increa se the strength of a

sma ll signal in a ra dio or t o provide ava ria ble cont rol for a m otor.

On some Toyota models, t ra nsistors a rebeing used t o provide var ia ble speedcont rol such a s th e AC blower m otor onthe Cr essida a nd t he electr ic motor tha trun s t he pow er steering pump on t he 1991MR2. By var ying t he emit ter-base currentof th e tra nsistor , the current f low ingthr ough t he motor can be varied, therebyva rying t he motor speed.

TRANSISTORS




INTEGRATED CIRCUITS

An int egra ted circuit ( IC) is nothin gmore tha n ma ny t r a nsis tors , diodes ,capa citors a nd r esistors connectedtogeth er wit h conductors an d placed on asin gle silicon chip. A sin gle IC is asystem within a system, wi th severa l tosevera l t housand electr ica l circuits built

into or onto a several-squaremillimetersil icon chip in a cera mic or pla st icpackage. The adva nt a ges of the IC a re thesize an d low cost of ma ss productiona long w i th low pow er consumpt ion a ndreliabil i ty . An IC can be an yt hing fromsimple logic gat e to a microprocessor toa lmost a complete computer on a chip.

ICs a re more re liab le than non-integra ted circuits beca use all th eelements ca n be built int o and ont o a

single silicon chip, thereby reducingcont a ct junct ions. In a ddit ion, thenumber of components is reduced.

ICs a re classif ied by t he number of part sincluded on one chip. The S ma ll Sca leInt egra t ion (SS I) IC ha s a bout 100element s; the Medium Sca le Int egrat ion(MSI ) IC ha s 100 to 1,000 elements; th eLa rge Sca le Integra t ion (LSI) IC ha s10,000 to 100,000 elements; and the VeryLa rge Sca le Int egra t ion (VLSI ) IC ha smore th a n 100,000 element s.

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TRANSISTORS




TRANSISTORS

ASSIGNMENT NAME:

1. Descr ibe the bas ic cons t ruct ion of a B ipola r Trans is tor .

2. D ra w a P NP Tr a nsist or a n d la bel it s pa r ts.

3 E xpla in t h e t w o cu rr en t pa t h s of a bipola r t ra n sis tor .

4. Expla in the purpose of the a r row on the emit t er and w hy i s the direct ion of itimportant .

5. I f t he a r row on the emit t er is point ing towa rd the base. Wha t t ype of t r ansistor isit a nd w ha t volta ge signal (positive or nega tive) is needed to the ba se in order toforwa rd bias the tra nsistor?

6. E x pla i n a nd pr ov ide a n exa m ple of “t r a nsis t or ga i n” .

7. D es cr ibe w h a t a n in t eg ra t ed cir cu it is .



COMPUTERS AND LOGIC CIRCUITS

Dea l ing wi th comput ers ca n seemoverwhelming for t hose w ho are

a c cus tomed t o wor king w i th mecha n ica lsys tems. Since we cann ot a c tual ly seew ha t is going on inside the comput er orth e system it cont rols , comput ers ma y notbe as easy t o under sta nd a s mechan ica lc omponents suc h a s t r a nsmiss ions a ndengines . H ow ever , computers a re not a scomplica ted a s th ey might sound. Thischa pter w il l help demyst i fy computers.

The comput ers found on a v ehicle a rereally no dif ferent t ha n a ny othercomput er encount ered in everyda y l i fe.Vehicle comput ers rely on da ta fromsome type of input device and th en follow the ins tru ct ions in t heir progra ms t odetermine t he required output . The inputdevice ma y be a keyboa rd or a coolan ttempera tur e sensor ,

a nd t he output ma y be video displa y or afuel injector . The progra m t he comput erfollows m a y be for w ord processing or forcont ro ll ing fuel meter ing a nd engine

t iming .

Computers ca n process a great deal o fda ta very quickly a nd a ccura tely , ma kingth em very us eful for severa l jobsinc luding cont ro ll ing ma ny of t hesyst ems on a n a ut omobile. This chapt erexpla ins how a comput er func t ions ,s ta r t ing wi th th e inputs a nd outputs , thecomputer 's centra l process ing uni t (CP U )a nd memory , a nd logic ga tes an d theirsymbols.

U nders ta nding how comput ers work isessentia l beca use most vehicles havesome type of computer . Kn ow ing how computers operat e and f i t t ogether w ithva r ious sensors a nd a c tua tors wi l lincrea se your a bil ity t o diag nose a ndrepair problems.

COMPUTERS A ND LOGIC CIRCUITS




This cha pter is divided int o the follow ingsections:

Ana log and D i g i t a l Inpu t s Ana log and D i g i ta l Outpu ts

S igna ls, in clu d i ng .

Ana l og and d i g i ta l w ave for ms

AI D conver ter s

D/A con ver ters

Microprocessor

Ra n dom Access M em ory (RAM )

Read -On ly Memor y (ROM )

Pr ogr amma ble Read -Onl y Memor y

(PROM)

Log ic C i rcu i t s

INPUTS

As demonstra ted in th e previous chapt er ,the EC U , as w ell as a ny o ther a utomobi lecomput er , depends on sensors t o monitorvar ious sys t em func t ions a nd repor t theirsta tus ba ck to the computer . Once thecomput er receives th e dat a from t hesensors , it a na lyzes i t a gains t pre-p r og r a m m e d s t a n d a r d s a n d a c t saccordingly .

One problem w ith m a ny of these inputs istha t t hey do not spea k the same langua gea s t he comput er . The comput er onlyund ersta nds d igita l s igna ls or on/offsignals. A resistive type sensor providesth e comput er

wi th a var ia ble vol ta ge, known a s ana na log s igna l . Some sensors , like th esw itch type sensors, do provide a d igita l

s ignal for the computer . In th is case , th ecomputer can in terpret the s igna lbeca use it is either on or it is off-nothin gin-between.

B eca use computers must ha ve digi ta linputs to use the dat a received, al l ana logsigna ls must be converted t o digita l . How computers in terpret th e ana log s ignalsw ith a n A/D convert er w ill be coveredla ter .

OUTPUTS

Computer output to most a ctua tors isdigita l . The signal tel ls the actua tor toeither t urn on for a specified lengt h oft ime or shut off . St epper motors, relaysa nd solenoids ha ve only t wo modes ofopera t ion: on or off .

Aga in , w hen a ctua to r s r equi r e a va r i ab levolt a ge, such a s th e speed cont rol for ablow er motor for a ir condit ioning, t he

computer n eeds a nother in terpreter . Inth is case, th e interpreter is a D/Aconverter , w hich w il l be covered lat er .

SIGNALS

As expla ined previously, t he t w o types ofs igna ls are an a log an d digi ta l . Thevol ta ge of these s igna ls ma y chan geslow ly or very q uickly depending on th esensor a nd w ha t i t moni tors . Whensigna ls ar e expressed a s w a ve forms ona n osci l loscope, the a na log s igna l showsup a s a f lowing l ine wi th curved pea ksa nd va l leys , indica t ing va r iable r ises anddrops in volta ge. The digita l s igna l ha sver t ica l r ises a nd drops , an d a hor izont a ll ine wit h sha rp corners. The tophorizont a l lines indicat e w hen th e volta geis high or on a nd t he bott om horizont a ll ines indicat e wh en th e volta ge is low oroff.





When using a vol tmeter t o measuredigita l or a na log s ignals tha t chan ge veryquickly, such a s speed sensor or RP M

signals , it i s impor ta nt to remember th a tthe meter rea ding is not a t ruerepresent a tion of th e signa l . A voltmet erdisplays t he a vera ge reading of thes igna l . For ex ample, w i th a d ig it a l s igna lth e voltmeter w il l display t he avera gebetween zero volts (off) and the voltagew hen t he circuit w a s on. The comput erlooks for "on" s igna ls , not volta ge. Thevolt met er, however, is looking for volta ge,not wh ether a s igna l c omes thr ough . Avoltmeter ma y show t ha t th e volta ge is

w ithin specif ica tions even i f a pulse ismiss ing. Tha t m iss ing s igna l couldrepresent th e ca use of a n engine problem.You might not know it by t he voltmeter ,causing you to a ssume incorrect ly t heproblem is e lsewh ere and w a ste t imesear c h ing .

So if you suspect th e problem is in acert a in circuit, but t he voltm eter does notshow it , consider using a n oscilloscopefor a more accura te rea ding. At the very

least , you should be aw a re of thisvol tmeter l imita t ion w i th d igi ta l s ignals .

When dea l ing wi t h computer s igna ls i t i sa lso impor ta nt to remember tha t there is

a dif ference betw een the signa l sourcea nd t he source of the volta ge on t he signa lw ire. This is especial ly import a nt w hen a

sensor input goes t o more th a n onecomput er , such a s a speed sensor s ignal ,or i f the signa l is from one comput er toa nother . One computer ma y supply t hevolta ge to the sensor wh ich t oggles thevolta ge to ground, a nd t he oth er computerma y jus t moni tor the s igna l . I f a wire isdisconnected from the comput er th a tsupplies volta ge to the sensor , the signa lis lost t o both comput ers. Do not m ista keth is for a defective comput er.

Ana log s igna ls a lso have l imi ta t ions intha t t heir inputs are not usa ble by thecomputer unt i l t r a ns la t ed in to d igita lsigna ls . The A/D convert er ha ndles t ha tt r ans l a t ion .

This t a kes us briefly ba ck to computerla ngua ge. Digit a l on/off can berepresent ed by th e bina ry numberingsys t em of 0 (off) a nd 1 (on). Any decima lnum ber (1, 2, 3, etc.) can be representedusing O's a nd 1's so the comput er

unders ta nds . The several t housandtra ns is tors ins ide th e computer 'smicroprocessor ca n sw itch on a nd off incombinat ions tha t equa l any binarynum ber in a microsecond.





The A/D convert er cha ng es th e a na logs ignal to th is binary la ngua ge by ta k ingsa mples of the an a log s ignal a t a

f requency known a s the sam pling ra te .The convert er measu res the w a ve anda ssigns a d igita l value to it . The higherthe sa mpling ra te , the c loser the digi ta ls ignal comes t o represent ing t he a na logone. In m ost cases each sa mple is dividedinto eight bits . E a ch bit is a ssigned eithera " 0" or a " 1" . These eight bit s a re ca l led aw ord. As i l lustra ted (below ), w henevert he A/D convert er sa mples t he sign a l, ita ss igns a b inary number to the vol tage a ttha t po int (wh ich t he computer reads a s a

ser ies of "ONs" a nd " OFFs" ), an d s l icesup the w a ve l ike a loaf of bread.

With th e signa l converted to eight-bitwords , the computer can use th e dat afrom t he sensor . The comput er t hensends out inst ructions in t he form of adigita l s igna l to a n a ctua tor . In mostcases th is w orks because most a c tuat orsa re solenoids or stepper motors w hichoperat e on digi ta l comma nds .

There a re, how ever , some component ssuch a s blow er motors or t he pow ersteering pump m otor on t he 1991 MR2,tha t require var ia ble volta ge to opera temotors a t va r iable speeds . In such ca ses ,t he comput er uses a D/A convert er t ochange t he digita l s ignal t o ana log. Theprinciples of D/A convert er opera t ion a ret he sa me a s t he A/D convert er. The

pulses of volta ge coming from th ecomputer a re converted t o var ia blevoltage.

THE MICROPROCESSORThe microprocessor is the hea rt of t hecomput er . I t is a lso cal led the centr a lprocessing un it (CP U ). Aga in, keep inmind tha t t he CP U does not per formcomplica ted opera tions. Inst ead , itperform s th ousan ds of s imple opera tionsincredibly fa st . To keep all of theopera t ions the CP U per forms f rombecoming enta ngled, i t execut es them inorder, pa ced by a clock.

The CP U can be divided int o threesections: th e contr ol section, thea r i thmetic a nd logic sect ion , a nd t heregister s ection.

The control section controls thecomput er 's ba sic opera t ions. I t ispr ogr a mmed w i th ins t r uc t ions f r om amemory t o ha ndle th ese chief operat ions:

Sendi ng dat a fr om one par t of the compu ter t o

another

Data in put an d output to and fr om the compu ter Ar i t hm et i c ca l cu l a t i ons

Ha l t i ng comput er opera t ions

Ju mp in g to ano ther i nst ru c t ion dur ing the

ru nn i n g of a p rogram

The a r i t hm etic an d logic section ca rr iesout the a ctua l process ing o f dat a , wh ichconsist s of ar i t hm etic opera tions an dlogical opera tions.





The register section temporarily storesda ta or program s unt i l they are sent t oth e ar i t hmet ic a nd logic section or thecont rol section

COMPUTER MEMORY

Computers ha ve their own f i ling sys tem,k n ow n a s " m e m o r y ," w h i c h is t h ein ter na l ci r cu i t r y w her e pr ogr a ms a ndda ta a re s tored. Computer memory isdivided into sepa ra te a ddresses to w hichdat a is sent y th e CPU . The CPU thenknows w here to find tha t da ta when i t i sneeded. Computers use their ma inmemories for la rge a mounts o f dat a orprogra m informa t ion. There are t wokinds o f memory : ra ndom a ccessmem ory (RAM) a nd r ea d-only memory

(ROM).

RANDOM ACCESS MEMORY (RAM)

RAM is memory w hich the comput er ca nboth read from a nd w rite t o. This isw here the comput er stores dat a receivedfront sensors , such a s engine RP M orcoola nt t empera tu re. RAM works l iketh ousa nds o f toggle swi tches which can

be either on or off to represent 0's a nd 1's.This is how th e dat a is s tored in RAM.The sw itches w ork l ike spring loadedsw itches, therefore th ey must be held inth e on" posit ion electr ical ly . I f pow er islost , everyth ing st ored in RAM is lost .

In most of the comput ers used onToyota s, th e RAM is divided into tw osections. One section receives its powerfrom the ignit ion sw itch. This is wh ereda ta a bout opera t ing condi t ions , such a svehicle speed an d coolan t tempera tur e, isst ored. The oth er section, called K eepAlive Memory, is powered directly by th eba t t ery . In forma t ion such a s d iagnost iccodes is s tored in Keep Alive Memory sotha t i t is retained a f ter the ignit ion is off .

This is why a fuse or ba tt ery ca ble ha s tobe removed to clear dia gnost ic codes.





READ-ONLY MEMORY (ROM)

This is w here th e basic operat inginst ructions for t he computer a re locat ed.

The inst ructions a re buil t int o the chipwhen i t i s ma nufac tur ed a nd c annot becha nged. The comput er ca n only read t heinforma t ion loca ted in ROM a nd can notwrite t o i t or use i t to store da ta . Since theinforma t ion in ROM is bui l t in dur ingma nufa cture , i t i s no t los t w hen pow er isremoved.

PROGRAMMABLE READ-ONLYMEMORY (PROM)

A P ROM is like a ROM except it ca n beprogra mmed or ha ve informa t ion wr i t t ent o it once. This is done before it isinst a l led in th e comput er . The comput ercan only read f rom the P ROM an d ca nnotwr ite to i t . The P ROM conta ins thespecif ic progra m inst ructions for thecomput er , such as the t iming a dva ncecurve for a par ticular engin e or th e shif tpoints for an a utoma t ic t ra nsmiss ion.There a re oth er ty pes of progra mm a ble

ROM being used, such a s erasa bleprogra mma ble rea d only memory(EP ROM) wh ich can be era sed byul tra violet light a nd reprogra mmed.Another t ype is electronica lly era sa bleprogra mma ble rea d only memory(EE P ROM) wh ich can be erasedelec tronica l ly a nd reprogra mmed. This isa ll done outside of th e computer by t hem a n u f a c t u r e r .

NON-VOLATILE MEMORY

Some computers use a type of RAM th a tis non-volat i le, meaning t ha t i t reta ins i tsmemory w hen t he power is removed.This t ype of memory ca n only be era sed bygoing t hrough a specif ic procedure. Thisis th e ty pe of memory u sed t o store code 41in the SRS a ir ba g sys tem on Cel ica a ndS u p r a .

LOGIC CIRCUITS

As comput ers a nd solid st a te cont rol

modules become more prevalent ona ut omobiles, some of th e logic gat esymbols tha t represent t heir

in terna l c ircuits w i l l show up more of ten .I t is necessary t o know n ot only wha t t helogic symbols sta nd for , but to understa ndth e basic opera tion of th e circuits t heyrepresent w hen you an a lyze w ir ingdiagrams dur ing t roubleshoot ing.Therefore, you should know a litt le a boutlogic circuits a nd t he symbols used to

represent th em. A logic gat e symbol iss imply a shor th a nd w a y of represent inga n electr onic circuit t ha t opera tes in acer ta in w ay . Un der sta nd ing the log icsymbols ca n ma k e under s ta nd ing theopera tion of a c ircuit mu ch quicker a ndeas ier tha n i f the c ircuit wererepresented by show ing a l l th etr a nsist ors , diodes an d resistors . Thelogic symbols shown in d ia gra ms in t heEWD a nd New C a r Fea ture book show wh a t pin vol tages must be present for a nelectr onic contr oller t o function properly.

Aga in , any th ing connec ted wi th acomput er is ba sed on t he digit a l on/offla ngu a ge. The sa me holds true for logicc ircui ts , wh ich a re ma de up oftra ns is tors combined in un i ts ca l led" ga tes. " These ga tes process tw o or mores igna ls logica l ly . In essence, they a resw itches. Depending on the input volta ge,th e ga te or swit ch will be eith er on or off .

The first th ing to lea rn a bout t he differentga tes is t heir symbols. Once you know th esymbols a nd how ea ch gat e works ,diagnosing a computer related problemw ill be easier .





Ta ken wit h permission from t heToyot a Adva nced E lectr ical C ourse#672





COMPUTERS AND LOGIC CIRCUITS

ASSIGNMENT NAME:

1. Ex pla in both the pur pose and d i ff er en t t ypes of inputs used by the computer .

2. N a m e t h e t y pe of ou t pu t s ig n a l mos t of t en u sed b y t he com pu t er .

3. N a m e t h e com pon en t s t h a t a r e t y pica l ly u sed a s ou t pu t d ev ices .

4. E xpla i n t h e d if fer en ce bet w e en An a l og a n d D ig it a l S ig na l s.

5. Ex pla in both the pur pose and c omplete name of an A/D c onver ter .

6. D ra w bot h a n An a log a nd Digit a l sign a l.

7. E xpla i n t h e bin a r y n um ber in g s ys t em a n d w hy it is us ed .

8. E x pla i n t h e f un ct ion of t h e M icr opr oces sor.

9. D escr ibe the pur pose of the RAM (Random Access Memor y)

10. Descr ibe the purpose of the ROM (Read Only Memory)

11. Descr ibe the purpose of the P ROM (P rogramma ble Read Only Memory)

12. Explain the bas ic funct ion and l ist the t ruth ta ble of an “AND” logic gat e ci rcui t .

13. Dra w the equivalent mecha nical ci rcui t of an “AND” logic gat e ci rcui t .

14. Explain the bas ic funct ion and l ist the t ruth ta ble of an “OR” logic gat e ci rcui t .

15. Dra w the equivalent mechanical ci rcui t of an “OR” logic gat e ci rcui t .

16. Descr ibe the bas ic funct ion a nd l is t the t ruth ta ble of a “NOT” logic gat e ci rcui t .

17. Descr ibe the bas ic funct ion a nd l is t the t ruth ta ble of a “NAND” logic gat e ci rcui t .

18. Descr ibe the bas ic funct ion a nd l is t the t ruth ta ble of a “NOR” logic gat e ci rcui t .

19. Descr ibe are the two bas ic components of a “FLIP-FLOP” logic gat e ci rcui t .



SENSORS AND ACTUATORS

Computer controlled systems continuallymonitor the operating condition of today's

vehicles. Through sensors, computersreceive vital information about a number of conditions, allowing minor adjustments to bemade far more quickly and accurately thanmechanical systems. Sensors converttemperature, pressure, speed, position andother data into either digital or analogelectrical signals.

A digital signal is a voltage signal that iseither on or off with nothing in between. A

switch is the simplest type of digital signalsensor. The signal from the switch could be0 volts when off and 12 volts when on. Analogsignals on the other hand have continuouslyvariable voltage. A good example is thecoolant temperature sensor. The coolanttemperature sensor may vary the voltagesignal anywhere between 0 volts and 5 voltsdepending on the temperature of the engine.

SENSORS & ACTUATORS




The digital signal is the easiest for thecomputer to understand because it reads thesignal as either "on" or "off." The analogsignal must be conditioned or converted todigital so the computer can understand it.

(This will be covered later.)

While a vehicle may have many differentsensors, there are three main categories:voltage-generating, resistive and switches. Avoltage-generating sensor generates its ownvoltage signal in relation to the mechanicalcondition it monitors. This signal in turnrelays to the computer data about thecondition of the system it controls. A resistivesensor reacts to changes in mechanicalconditions through changes in its resistance.The computer supplies a regulated voltageor reference voltage to the sensor andmeasures the voltage drop across thesensor to determine the data.

Switch sensors toggle a voltage from thecomputer high or low, or supply an "on" or "off" voltage signal to the computer. This typeof sensor may be as simple as a switch onthe brake pedal or as complex as aphototransistor speed sensor.

The computer uses the sensor data tocontrol different systems on a vehiclethrough the use of actuators. An actuator isan electromechanical device such as a relay,solenoid or motor. Actuators can adjustengine idle speed, change suspensionheight or regulate the fuel metered into theengine.

This chapter describes several specificsensors used in automobiles, such aspotentiometers, thermistors andphototransistor / LED combinations. Thischapter also addresses actuators thatcomplete the control process by carrying outthe computer's instructions.

The Sensors and Actuators section is dividedinto the following areas:

Resistive sensors: potentiometers

thermistorspiezo resistive

Voltage generating sensors: piezo electriczirconia-dioxidemagnetic inductance

Switch sensors:

phototransistors and LEDsspeed sensorsG-sensors (Air Bag Impact Sensors)

Actuators: stepper motorssolenoids

RESISTIVE SENSORS

Potentiometers

A potentiometer is a variable resistor that iscommonly used as a sensor. Apotentiometer has three terminals: one for power input, one for a ground and one toprovide a variable voltage output. Apotentiometer is a mechanical device whoseresistance can be varied by the position of the movable contact on a fixed resistor. Themovable contact slides across the resistor tovary the resistance and as a result varies the

voltage output of the potentiometer. Theoutput becomes higher or lower dependingon whether the movable contact is near theresistor's supply end or ground end.

SENSORS & ACTUATORS




The vane type air flow meter on an EFI

equipped vehicle is a common location on aToyota for a sensor that uses apotentiometer. This sensor converts the air flow meter vane opening angle to a voltageand sends it to the Electronic Control Unit(ECU). This signal allows the ECU todetermine the volume of air that is enteringthe engine.

Some models also use a potentiometer asthe throttle position sensor. The

potentiometer in this case is attached to thethrottle shaft of the throttle body. As the shaftis rotated the voltage output of thepotentiometer changes. The voltage output of the potentiometer supplies data to the ECUabout the throttle opening angle.

Thermistors

Thermistors are variable resistors whoseresistance changes in relation totemperature. Thermistors can have either a

negative temperature coefficient (NTC) or apositive temperature coefficient (PTC). Athermistor with a negative temperaturecoefficient will decrease in resistance as thetemperature is increased. On the other hand,a thermistor with a positive temperaturecoefficient will increase in resistance as thetemperature is increased. The thermistor hastwo terminals, one for power and one for ground. A reference voltage is supplied toone terminal through a fixed series resistor located inside the computer. The other terminal of the thermistor is connected toground, usually back through the computer.The computer monitors the voltage after theinternal fixed resistor and compares thisvoltage to the reference voltage to determinethe temperature of the thermistor. Therelationship between the two voltageschanges as the temperature of the thermistor changes.

SENSORS & ACTUATORS




The coolant temperature sensor and the air temperature sensor in the air flow meter areboth NTC thermistors. Thermistors are alsoused as sending units for temperaturegauges such as the coolant temperature

gauge. The TCCS ECU uses data from thecoolant temperature sensor and air temperature sensor to help determine theproper amount of fuel and how long to openthe fuel injectors. The ECU also uses thisdata to determine how much the ignitiontiming should be advanced as well as theproper setting for the ISC to maintain theproper idle speed. When either the air temperature or the coolant temperature islow, the respective thermistor's resistanceincreases and the computer receives a highvoltage signal at the respective sensor wire.Conversely, a high temperature at either sensor results in a low voltage signal due tothe lower resistance of the thermistor.

Piezo Resistive

A piezo resistive sensor is a resistor circuitconstructed on a thin silicon wafer. Physicallyflexing or distorting the wafer a small amountchanges its resistance. This type of sensor is usually used as a pressure sensingdevice such as a manifold pressure sensor,although it may also be used to measureforce or flex in an object such as thedeceleration sensor located in the SRS air bag center sensor.

One of the most important piezo resistivesensors is the manifold pressure sensor which monitors the air intake volume for

Electronic Fuel Injection (EFI). The signal itsends to the ECU determines the basic fuelinjection duration and ignition advanceangle.

Within the sensor is a silicon chip combinedwith a vacuum chamber. One side of the chipis exposed to the intake manifold pressureand the other side to the internal perfectvacuum in the chamber.

A change in the intake manifold pressurecauses the shape of the silicon chip tochange, with the resistance value of the chipfluctuating in relation to the degree of deformation. An integrated circuit converts the

fluctuation to a voltage signal that is sent tothe ECU, where the air-fuel ratio is regulated.The sensor has three external terminals: onefor power, one for ground and one to providethe voltage signal to the computer. Thevoltage signal varies with the pressure in theintake manifold.

Another use for this same type of sensor is tosense turbocharger boost. On turbochargedengines, the sensor is used to measurepressures that are higher than atmosphericpressure and to supply correspondingvoltage signals to the ECU. To preventengine damage, the ECU can cut off the fuelbeing injected if the manifold pressurebecomes too high.

SENSORS & ACTUATORS




VOLTAGE GENERATING SENSORS

Piezo Electric

Piezo electricity is generated by pressure oncertain crystals, such as quartz, which willdevelop a potential difference, or voltage, onthe crystal face. When the crystal flexes or vibrates, an AC voltage is produced.

Knock sensors, which are becoming morecommon, take advantage of thisphenomenon by sending the ECU a signalthat engine knock is occurring. The ECU inturn retards the ignition timing to stop theknocking. Knock sensors contain a piezoelectric element which, when deformed bycylinder block vibration caused by knocking,generates a voltage.

There are two styles of knock sensors used.The mass type produces a voltage outputover wide range, but the signal is greatest at

a vibration of approximately 7 kHz. The other style is the resonance type which onlyproduces a significant voltage signal whenexposed to a vibration of approximately 7kHz. Since the voltage output from either knock sensor varies continually, the systemis highly susceptible to electromagnetic andradio interference. The computer can be

fooled by these stray electrical signals if theyget mixed with the knock sensor signal. For this reason the signal wire running from thesensor to the ECU is a special ground-shielded type. The shield surrounds the

signal wire and is connected to ground soany electrical interference is taken to ground.If this shield is damaged or not grounded, theelectrical interference can reach the ECU andcause it to retard the timing unnecessarily.

Oxygen Sensors

The oxygen sensor, located in the exhaustmanifold, senses whether the air-fuel ratio isrich or lean, and sends signals to the ECUwhich in turn makes minor corrections to theamount of fuel being metered. This isnecessary for the three-way catalyticconverter to function properly.

There are two kinds of oxygen sensors:zirconia and titania. The zirconia oxygensensor is constructed in a bulb configurationfrom zirconia dioxide. A thin platinum plate isattached to both the inside and outside of thebulb. The inner area is exposed to theatmosphere and the outside is exposed tothe exhaust. When the sensor is heated toapproximately 600˚F, electrically

SENSORS & ACTUATORS




charged oxygen ions form on the platinumplates. The amount of oxygen to which eachplate is exposed determines how many ionsform on the plates. When there is adifference in the number of ions on the

plates, a difference in potential or voltageoccurs between the two plates. The lessoxygen there is in the exhaust, the greater thevoltage produced. When the air-fuel mixtureis lean, the voltage created is low.Conversely, when the mixture is rich, thevoltage is high.

The titania oxygen sensor does not producea voltage. Instead, it undergoes a change inresistance in relation to the oxygen content inthe exhaust. This type of oxygen sensor isreferred to as a thick film sensor. It consistsof a piece of titania with two wires connectedto it located at the end of an insulator. Thesensor is not exposed to the atmosphereonly to the exhaust. Because the operatingtemperature must remain constant, thesensor has an electric heater. After the

sensor is at operating temperature, theamount of oxygen to which the titania isexposed. will change the physical resistanceof the sensor. The ECU supplies a referencevoltage to the sensor and monitors the

voltage at the signal wire, similar to athermistor.

Magnetic Inductance

Magnetic inductance sensors consist of acoil of wire around an iron core plus apermanent magnet. The magnet can beeither stationary or movable. If the magnet isthe moving member, as it passes the coil themagnetic lines of force cut through the coiland a voltage is produced. Since the northand south poles of the magnet alternate asthey pass the coil, the voltage polarity alsoalternates. As the speed of the magnetrotating past the coil is increased a larger voltage is produced and the frequency of thevoltage polarity changes is increased. Thissame type of sensor can also work if themagnet is stationary and attached to the coreof the coil. When a toothed reluctor, or rotor (made from a magnetic material) is rotatedpast the coil and magnet, the magnetic linesof force move and cut through the coil. Thelines of force cutting through the coil willproduce the same type of voltage output aswhen the magnet was moving.

SENSORS & ACTUATORS




This type of sensor is commonly used as awheel speed sensor on ABS equippedvehicles. This sensor is also used in the

distributor to determine RPM and crankshaftposition. Since the voltage output of thissensor is varying continually and is low atlow speeds, the computer must be able tosense the small voltage. If electricalinterference is allowed to combine with thesignal voltage, the computer could be fooled.To prevent stray electrical interference, thesignal wire usually has a ground shieldformed around it like the knock sensor.

SWITCH TYPE SENSORS

Phototransistor and LED

As discussed in the previous chapter, aphototransistor is a transistor that isactivated or turned on by light. Whencombined with a LED and a rotating slottedwheel in a vehicle speed sensor, aphototransistor can supply vehicle speeddata to a computer.

In this type of sensor the LED is aimed at thephototransistor. When the slotted wheel isrotated by the speedometer cable, it breaks

the beam of light. The beam of light isinterrupted 20 times per revolution. The ECUsupplies a reference voltage to the collector of the phototransistor and the emitter isconnected to ground. Each time the light hits

the phototransistor, it turns it on just like atoggle switch. Each time the phototransistor is turned on, the wire from the ECU isconnected to ground and the voltage is pulleddown to 0 volts. The ECU can count thesepulses and calculate vehicle speed.

This type of sensor is also used as a GSensor or deceleration sensor on the Celica

All Trac and Trucks equipped with ABS. Thissensor has two LEDs aimed at twophototransistors that are separated by aslotted plate on a fulcrum. When the vehicleis decelerated, the plate pivots on the fulcrumand the slots in the plate line up with one or the other or both of the LEDs andphototransistors-depending on the rate of deceleration. These signals are sent to thecomputer so it can determine thedeceleration rate for ABS to operate properly.

SENSORS & ACTUATORS




Reed Switches

The reed switch is commonly used as aspeed sensor or position sensor. It consistsof a set of contacts that open when adjacent

to a magnet. In the speed sensor application, the magnet is attached to thespeedometer cable and rotates with thecable. Each time one of the poles of themagnet passes the switch the contacts openand then close. A voltage is supplied to onecontact on the switch and the other contact isconnected to ground. Each time the pointsclose, the voltage is pulled down to 0 volts,

just like the phototransistor speed sensor.

ACTUATORS

Stepper Motor

Essentially, stepper motors are digitalactuators; in other words, they are either onor off. They move in fixed increments in both

directions, and can have over 120 steps of motion.

Stepper motors are commonly used toenable the ECU to control idle speed. In mostfuel injection systems, the stepper motor controls an idle air bypass built into thethrottle body.

SENSORS & ACTUATORS




In an idle speed control valve (ISCV), (locatedin the air intake chamber) a stepper motor isbuilt into the ISCV where it rotates a valveshaft either in or out. This in turn increasesor decreases the clearance between the

valve and the valve seat, thereby regulatingthe amount of air allowed to pass through.The ISCV stepper motor allows 125 possiblevalve opening positions.

Solenoids

Like stepper motors, solenoids are digitalactuators. One terminal is attached to batteryvoltage while the other is attached to thecomputer which opens and closes theground circuit as needed. When energized,the solenoid may extend a plunger or armature to control functions such asvacuum flow to various emission-relatedsystems or fuel injection. Most actuators aresolenoids.

Solenoids are controlled two ways: pulsewidth or duty cycle. Pulse width control isused when the frequency is not consistent.

An example of pulse width is a fuel injector which is turned on for a determined length of

time and then shut off. Duty cycle control isused when the frequency does remainconstant. A duty cycle solenoid in ABS isdesigned to be on and off for a specific timeaccording to a selected ratio-on for 20% of the time and off the other 80%.

Idle speed control valves can be constructedwith a solenoid instead of a stepper motor. Inthis case, the function is the same: the ECUsends a signal to the ISCV to control theintake air.

Solenoid valves are also used in ECTtransmissions. Shifting is controlled by thesolenoid as it opens or closes a hydraulicpassage to control oil flow to the shift valves.

SENSORS & ACTUATORS




SENSORS & ACTUATORS A SSIGNMENT NAME:

1. Describe the term “Digital Signal” and provide an example.2. List three types of “Resistive senors” and provide an example of each.

3. List three “types of Voltage generating sensors” and provide an example of each.

4. List three types of “Switch sensors” and provide an example of each.

5. List two types of “Actuators” and provide an example of each.

6. Describe the operation of both types of “thermistors” and draw an example of theelectrical circuit.

7. Explain the operation of a “Piezo Resistive” sensor.

8. Explain how a “Piezo Resistive” sensor differs from a “Piezo Electric” sensor.

9. Describe the operation and construction of the two basic types of Oxygen Sensors.

10. Outline the construction and common uses of a “Magnetic Inductance” sensor.

11. Outline the construction and common uses of a “Phototransistor” switch.

12. Explain the operation of a “Reed” switch and how they are used.

13. Describe the basic operation of a “stepper motor” and how they are used.

14. Explain two ways in which solenoids can be controlled.



Electronic Control Transmission (ECT)

The Electronic Control Transmission is an automatic transmission which uses modernelectronic control technologies to control the transmission. The transmission itself, except for the valve body and speed sensor, is virtually the same as a full hydraulically controlledtransmission, but it also consists of electronic parts, sensors, an electronic control unit andactuators.

The electronic sensors monitor the speed of the vehicle, gear position selection and throttleopening, sending this information to the ECU. The ECU then controls the operation of theclutches and brakes based on this data and controls the timing of shift points and torqueconverter lock-up.

Driving Pattern Select SwitchThe pattern select switch is controlled by the driver to select the desired driving mode, either "Normal" or "Power." Based on the position of the switch, the ECT ECU selects the shift patternand lock-up accordingly. The upshift in the power mode will occur later, at a higher speeddepending on the throttle opening. For example, an upshift to third gear at 50% throttle willoccur at about 37 mph in normal mode and about 47 mph in power mode.

TOYOTA ELECTRONIC CONTROL TRANSMISSION




The ECU has a "PWR" terminal but does not have a "Normal" terminal. When "Power" isselected, 12 volts are applied to the "PWR" terminal of the ECU and the power light illuminates.

When "Normal" is selected, the voltage at "PWR" is 0 volts. When the ECU senses 0 volts at theterminal, it recognizes that "Normal" has been selected.

Beginning with the 1990 MR2 and Celica and the 1991 Previa, the pattern select switch wasdiscontinued. In the Celica and Previa systems, several shift patterns are stored in the ECUmemory. Utilizing sensory inputs, the ECU selects the appropriate shift pattern and operatesthe shift solenoids accordingly. The MR2 and 1993 Corolla have only one shift pattern stored inthe ECU memory.

Neutral Start SwitchThe ECT ECU receives information on the gear range into which the transmission has been

shifted from the shift position sensor, located in the neutral start switch, and determines theappropriate shift pattern. The neutral start switch is actuated by the manual valve shaft inresponse to gear selector movement.

The ECT ECU only monitors positions "T' and "L." If either of these terminals provides a 12-voltsignal to the ECU, it determines that the transmission is in neutral, second gear or first gear. If the ECU does not receive a 12-volt signal at terminals "T' or "1," the ECU determines that thetransmission is in the "D" range.

Some neutral start switches have contacts for all gear ranges. Each contact is attached to thegear position indicator lights if the vehicle is so equipped.





In addition to sensing gear positions, the neutral switch prevents the starter from cranking theengine unless it is in the park or neutral position. In the park and neutral position, continuity isestablished between terminals "B" and "NB" of the neutral start switch illustrated below.

Throttle Position Sensor This sensor is mounted on the throttle body and electronically senses how far the throttle isopen and then sends this data to the ECU. The throttle position sensor takes the place of throttle pressure in a fully hydraulic control transmission. By relaying the throttle position, itgives the ECU an indication of engine load to control the shifting and lock-up timing of thetransmission.

There are two types of throttle sensors associated with ECT transmissions. The type is relatedto how they connect to the ECT ECU. The first is the indirect type because it is connecteddirectly to the engine ECU, and the engine ECU then relays throttle position information to theECT ECU. The second type is the direct type which is connected directly to the ECT ECU.





Indirect Type

This throttle position sensor converts the throttle valve opening angle into voltage signals. It has

four terminals: VC, VTA, IDL and E. A constant 5 volts is applied to terminal VC from the engineECU. As the contact point slides along the resistor with throttle opening, voltage is applied tothe VTA terminal. This voltage increases linearly from 0 volts at closed throttle to 5 volts at wide-open throttle.

The engine ECU converts the VTA voltage into one of eight different throttle opening anglesignals to inform the ECT ECU of the throttle opening. These signals consist of variouscombinations of high and low voltages at ECT ECU terminals as shown in the chart below. Theshaded areas of the chart represent low voltage (about 0 volts). The white areas represent highvoltage (L1, L2, U: about 5 volts; IDL: about 12 volts).





When the throttle valve is completely closed, the contact points for the IDL signal connect theIDL and E terminals, sending an IDL signal to the ECT ECU to inform it that the throttle is fullyclosed.

As the ECT ECU receives the L1, L2 and D signals, it provides an output voltage from 1 to 8volts at the TT or ECT terminal of the diagnostic check connector. The voltage signal variesdepending on the throttle opening angle and informs the technician whether or not the throttleopening signal is being input properly.

Direct Type

With this type of throttle sensor, signals are input directly to the ECT ECU from the throttleposition sensor. Three movable contact points rotate with the throttle valve, causing contactsL1, L2, L3 and IDL to make and break the circuit with contact E (ground). The grid which thecontact points slide across is laid out in such a way as to provide signals to the ECT ECU

depicted in the chart below. The voltage signals provided to the ECT ECU indicate throttleposition just as they did in the indirect type of sensor.

If the idle contact or its circuit on either throttle sensor malfunctions, certain symptoms occur. If it is shorted to ground, lock-up of the torque converter will not occur. If the circuit is open, neutralto drive squat control does not occur and a harsh engagement may be the result. If the L1, L2,L3 signals are abnormal, shift timing will be incorrect.





Water Temperature Sensor The water temperature sensor monitors engine coolant temperature and is typically locatednear the cylinder head water outlet. A thermistor is mounted within the temperature sensor, and

its resistance value decreases as the temperature increases. Therefore, when the enginetemperature is low, resistance will be high.

When the engine coolant is below a predetermined temperature, the engine performance andthe vehicle's drivability would suffer if the transmission were shifted into overdrive or theconverter clutch were locked-up. The engine ECU monitors coolant temperature and sends asignal to terminal OD1 of the ECT ECU. The ECU prevents the transmission from upshifting

into overdrive and lock-up until the coolant has reached a predetermined temperature. Thistemperature will vary from 122'F to 162’F depending on the transmission and vehicle model.For specific temperatures, refer to the ECT Diagnostic Information chart in the appendix of thisbook.

Some models, depending on the model year, cancel upshifts to third gear at lower temperatures. This information is found in the appendix and is indicated in the heading of theOD Cancel Temp column of the ECT Diagnostic Information chart by listing in parenthesis thetemperature for restricting third gear.





Speed SensorsTo ensure that the ECT ECU is kept informed of the correct vehicle speed at all times, vehiclespeed signals are input into it by two speed sensors. For further accuracy, the ECT ECU

constantly compares these two signals to see whether they are the same. The speed sensor isused in place of governor pressure in the conventional hydraulically controlled transmission.

Main Speed Sensor (No. 2 Speed Sensor)

The main speed sensor is located in the transmission housing. A rotor with built-in magnet ismounted on the drive pinion shaft or output shaft. Every time the shaft makes one completerevolution, the magnet activates the reed switch, causing it to generate a signal. This signal is

sent to the ECU, which uses it in controlling the shift point and the operation of the lock-upclutch. This sensor outputs one pulse for every one revolution of the output shaft.

Beginning with the 1993 Corolla A245E, the No. 2 speed sensor has been discontinued andonly the No. 1 speed sensor is monitored for shift timing.





Back- Up Speed Sensor (No.1 Speed Sensor)

The back-up speed sensor is built into the combination meter assembly and is operated by thespeedometer cable. The sensor consists of an electrical reed switch and a multiple pole

permanent magnet assembly. As the speedometer cable turns, the permanent magnet rotatespast the reed switch. The magnetic flux lines between the poles of the magnet cause thecontacts to open and close as they pass. The sensor outputs four pulses for every onerevolution of the speedometer cable.

The sensor can also be a photocoupler type which uses a photo transistor and light-emittingdiode (LED). The LED is aimed at the phototransistor and separated by a slotted wheel. Theslotted wheel is driven by the speedometer cable. As the slotted wheel rotates between theLED and photo diode, it generates 20 light pulses for each rotation. This signal is convertedwithin the phototransistor to four pulses sent to the ECU.

Speed Sensor FailsafeIf both vehicle speed signals are correct, the signal from the main speed sensor is used in shifttiming control after comparison with the output of the back-up speed sensor. If the signals fromthe main speed sensor fail, the ECU immediately discontinues use of this signal and uses thesignals from the back-up speed sensor for shift timing.





Stop Light SwitchThe stop light switch is mounted on the brake pedal bracket. When the brake pedal isdepressed, it sends a signal to the STP terminal of the ECT ECU, informing it that the brakes

have been applied.

The ECU cancels torque converter lock-up when the brake pedal is depressed, and it cancels"N" to "D" squat control when the brake pedal is not depressed and the gear selector is shiftedfrom neutral to drive.

Overdrive Main SwitchThe overdrive main switch is located on the gear selector. It allows the driver to manually controloverdrive. When it is turned on, the ECT can shift into overdrive. When it is turned off, the ECT isprevented from shifting into overdrive.





O/D Main Switch ON

When the O/D switch is in the ON position, the electrical contacts are actually open and currentfrom the battery flows to the OD2 terminal of the ECT ECU as shown below.

O/D Main Switch OFF

When the O/D switch is in the OFF position, the electrical contacts are actually closed andcurrent from the battery flows to ground and 0 volts is present at the OD2 terminal as shownbelow. At the same time, the O/D OFF indicator is illuminated.

Solenoid ValvesSolenoid valves are electro-mechanical devices which control hydraulic circuits by opening adrain for pressurized hydraulic fluid. Of the solenoid valves, No. 1 and No. 2 control gear shiftingwhile No. 3 controls torque converter lock-up.





No. 1 and No. 2 Solenoid Valves These solenoid valves are mounted on the valve body and are turned on and off by electricalsignals from the ECU, causing various hydraulic circuits to be switched as necessary. By

controlling the two solenoids' on and off sequences, we are able to provide four forward gearsas well as prevent upshifts into third or fourth gear.

The No. 1 and No. 2 solenoids are normally closed. The plunger is spring loaded to the closed

position, and when energized, the plunger is pulled up, allowing line pressure fluid to drain.The operation of these solenoids by the ECT ECU is described on pages 16- 19.

No. 3 Solenoid Valve

This solenoid valve is mounted on the transmission exterior or valve body. It controls linepressure which affects the operation of the torque converter lock-up system. This solenoid iseither a normally open or normally closed solenoid. The A340E, A340H, A540E and A540Htransmissions use the normally open solenoid.

No. 4 Solenoid Valve

This solenoid is found exclusively on the A340H transfer unit described on page 152 of this

book. This solenoid is a normally closed solenoid which controls the shift to low 4-wheel drive.It is controlled by the ECT ECU when low 4-wheel drive has been selected at vehicle speedsbelow 18 mph with light throttle opening.





Functions of ECT ECU

Control of Shift Timing

The components which make up this system include:

• OD main switch• OD Off indicator light• ECT ECU• Water temperature sensor • Cruise control ECU• No. 1 and No. 2 solenoid valves (shift solenoids)

The ECU controls No. 1 and No. 2 solenoid valves based on vehicle speed, throttle openingangle and mode select switch position.

The ECT ECU prevents an upshift to overdrive under the following conditions:

• Water temperature is below 122'F to 146*F*.• Cruise control speed is 6 mph below set speed.• OD main switch is off (contacts closed).

In addition to preventing the OD from engaging below a specific engine temperature, upshift tothird gear is also prevented in the Supra and Cressida below 96'F and the V6 Camry below100’F.

* Consult the specific repair manual or the ECT Diagnostic Information Technician ReferenceCard for the specific temperature at which overdrive is enabled.





Control of Lock-UpThe ECT ECU has lock-up clutch operation pattern for each driving mode (Normal and Power)programmed in its memory. The ECU turns the No. 3 solenoid valve on or off according to

vehicle speed and throttle opening signals. The lock-up control valve changes the fluidpassages for the converter pressure acting on the torque converter piston to engage or disengage the lock-up clutch.

In order to turn on solenoid valve No. 3 to operate the lock-up system, the following threeconditions must exist simultaneously:

• The vehicle is traveling in second, third, or overdrive ("D" range).

• Vehicle speed is at or above the specified speed and the throttle opening is at or above thespecified value.

• The ECU has received no mandatory lock-up system cancellation signal.

The ECU controls lock-up timing in order to reduce shift shock. If the transmission up-shifts or down-shifts while the lock-up is in operation, the ECU deactivates the lock-up clutch.





The ECU will cancel lock-up if any of the following conditions occur:

• The stop light switch comes on.

• The coolant temperature is below 122'F to 145’F depending on the model. Consult the vehiclerepair manual or the ECT Diagnostic Information Technician Reference Card.

• The IDL contact points of the throttle position sensor close.

• The vehicle speed drops about 6 mph or more below the set speed while the cruise controlsystem is operating.

The stop light switch and IDL contacts are monitored in order to prevent the engine from stallingin the event that the rear wheels lock up during braking. Coolant temperature is monitored to

enhance drivability and transmission warm-up. The cruise control monitoring allows the engineto run at higher rpm and gain torque multiplication through the torque converter.

Neutral to Drive Squat ControlWhen the transmission is shifted from the neutral to the drive range, the ECU prevents it fromshifting directly into first gear by causing it to shift into second or third gear before it shifts to firstgear. It does this in order to reduce shift shock and squatting of the vehicle.

Engine Torque ControlTo prevent shifting shock on some models, the ignition timing is retarded temporarily duringgear shifting in order to reduce the engine's torque. The TCCS and ECT ECU monitors engine

speed signals (Ne) and transmission output shaft speed (No. 2 speed sensor) thendetermines how much to retard the ignition timing based on shift pattern selection and throttleopening angle.





Fail-Safe OperationThe ECT ECU has several fail-safe functions to allow the vehicle to continue operating even if amalfunction occurs in the electrical system during driving. The speed sensor fail-safe has

already been discussed on page 8.

Solenoid Valve Back-Up FunctionIn the event that the shift solenoids malfunction, the ECU can still control the transmission byoperating the remaining solenoid to put the transmission in a gear that will allow the vehicle tocontinue to run.

The chart below identifies the gear position the ECU places the transmission if a givensolenoid should fail. Notice that if the ECU was not equipped with fail-safe, the items inparenthesis would be the normal operation. But because the ECU senses the failure, itmodifies the shift pattern so the driver can still drive the vehicle. For example, if No. 1 solenoidfailed, the transmission would normally go to overdrive in drive range first gear. But instead, No.2 solenoid turned it on to give 3rd gear.

Should both solenoids malfunction, the driver can still safely drive the vehicle by operating theshift lever manually.





ECT Shift Valve OperationTwo electrically operated solenoids control the shifting of all forward gears in the Toyotaelectronic control four speed automatic transmission. These solenoids are controlled by an

ECU which uses throttle position and speed sensor input to determine when the solenoids areturned on. The solenoids normal position is closed, but when it is turned on, it opens to drainfluid from the hydraulic circuit. Solenoid No. 1 controls the 2-3 shift valve. It is located betweenthe manual valve and the top of the 2-3 shift valve. Solenoid No. 2 controls the 1-2 shift valveand the 3-4 shift valve.

First Gear

During first gear operation, solenoid No. 1 is on and solenoid No. 2 is off. With line pressuredrained from the top of the 2-3 shift valve by solenoid No. 1, spring tension at the base of thevalve pushes it upward. With the shift valve up, line pressure flows from the manual valvethrough the 2-3 shift valve and on to the base of the 3-4 shift valve.

With solenoid No. 2 off, line pressure pushes the 1-2 shift valve down. In this position, the 1-2shift valve blocks line pressure from the manual valve. Line pressure and spring tension at thebase of the 3-4 shift valve push it upward.





Second Gear

During second gear operation, solenoid No. 1 and No. 2 are on. Solenoid No. 1 has the same

effect that it had in first gear with the 2-3 shift valve being held up by the spring at its base.Pressure from the manual valve flows through the 2-3 shift valve and holds the 3-4 shift valveup.

With solenoid No. 2 on, line pressure from the top of the 1-2 shift valve bleeds through thesolenoid. Spring tension at the base of the 1-2 shift valve pushes it upward. Line pressurewhich was blocked, now is directed to the second brake (132), causing second gean The 3-4shift valve maintains its position with line pressure from the 2-3 shift valve holding it up.





Third Gear

During third gear operation, solenoid No. 1 is off and solenoid No. 2 is on. When solenoid No. 1is off, it closes its drain and line pressure from the manual valve pushes the 2-3 shift valve

down. Line pressure from the manual valve is directed to the direct clutch (C2) and to the baseof the 1-2 shift valve.

With solenoid No. 2 on, it has the same effect that is had in second gear; pressure is bled atthe top of the 1-2 shift valve and spring tension pushes it up. Line pressure is directed to thesecond brake (B2). However in third gear, the second brake (B2) has no effect since it holds theone-way clutch No. 1 (Fl) and freewheels in the clockwise direction. The second coast brake isready in the event of a downshift when the OD direct clutch (C2) is released.





Fourth Gear During fourth gear operation, both solenoids are off. When solenoid No. 1 is off, its operation isthe same as in second and third gears.

A third solenoid controls lock-up operation.

Reprinted with permission by Toyota Motor Sales, USA, Inc.,from the Automatic Transmission Course #262 textbook.





Checks and AdjustmentsThe transmission requires regular maintenance intervals if it is to continue to operate withoutfailure. As we discussed in previous sections, transmission fluid loses certain properties over

time and especially due to heat.

The Maintenance Schedules found in the repair manual or the Owners Manual indicate theappropriate replacement schedules based on how the vehicle is used. Schedule A for example,recommends replacement of the fluid every 20,000 miles or 24 months. Whereas Schedule Brecommends just an inspection of the fluid every 15,000 miles or 24 months and noreplacement interval.

The chart below indicates which maintenance schedule to follow based on the use of thevehicle.

TOYOTA ELECTRONIC TRANSMISSION CHECKS & DIAGNOSIS




Fluid Level

The fluid level in the automatic transmission should be inspected by means of the dipstick after

the transmission has been warmed up to ordinary operating temperature, approximately 158'Fto 176'F. As a rule of thumb, if the graduated end is too hot to hold, the fluid is at operatingtemperature. The fluid level is proper if it is in the hot range between hot maximum and hotminimum.

NOTE: The cool level found on the dip stick should be used as a reference only when thetransmission is cold. The correct fluid level can only be found when the fluid is hot.

It is important to keep the fluid at the correct level at all times to ensure proper operation of theautomatic transmission. If the fluid level is too low, the oil pump will draw in air, causing air tomix with the fluid. Aerated fluid lowers the hydraulic pressure in the hydraulic control system,causing slippage and resulting in damage to clutches and bands. If the fluid level is excessive,planetary gears and other rotating components agitate the fluid, aerating it and causing similar symptoms as too little fluid. In addition, aerated fluid will rise in the case and may leak from the

breather plug at the top of the transmission or through the dipstick tube.

In addition, be sure to check the differential fluid level in a transaxle. This fluid is sealed off andseparate from the transmission cavity in some applications.





Throttle Cable

The throttle cable is adjustable on all automatic transmissions. And in each case it controlsthrottle pressure. Throttle pressure is an indication of load. When the throttle is depressed, the

cable transfers this motion to the base of the throttle valve and moves it upward to increasethrottle pressure. Throttle pressure causes the primary regulator valve to increase linepressure. As the throttle is depressed, greater torque is produced by the engine and thetransmission may also downshift to a lower gear. If line pressure did not increase, slippagecould occur which would result in wear of the clutch plate surface material.

Throttle pressure's affect on transmission operation differs between a hydraulically controlledtransmission (non-ECT) and an electronically controlled transmission (ECT). In a non-ECTtransmission, throttle pressure affects shift points and line pressure; whereas in an ECTtransmission it only affects line pressure. Control of line pressure will affect the quality of theshift, not the shift points, in an ECT transmission.





Inspect and Adjust the Throttle Cable

To inspect the throttle cable adjustment, the engine should be off. Depress the accelerator pedal completely, and make sure that the throttle valve is at the maximum open position. If the

throttle valve is not fully open, adjust as needed.

With the throttle fully open, check the throttle cable stopper at the boot end and ensure that thereis no more than one millimeter between the end of the stopper and the end of the boot. If adjustment is required, make the adjustment with the throttle depressed. Loosen the lockingnuts on the cable housing and reposition the cable housing and boot as needed until thespecification is reached.

The Land Cruiser A440 automatic transmission throttle cable is adjusted differently, as seenbelow. It is measured in two positions. The first measurement is made with the throttle fullyclosed. The distance varies in that the measurement is made from the end of the boot to the

front of the stopper. Measure the same distance with the throttle in the fully open position.

The illustration below represents yet another adjustment type. The rubber boot has a shallowextension when compared to the first one discussed earlier. The procedure differs in that thethrottle is left in the fully closed position when the distance is measured from the front of theboot to the front of the stopper.





Inspect and Adjust the Shift Cable To inspect the shift cable, move the gear selector from neutral to each position. The gear

selector should move smoothly and accurately to each gear position. Adjust the shift cable inthe indicator does not line-up with the position indicator while in the proper detent. To adjust,loosen the swivel nut on the shift linkage. Push the manual lever at the transmission fullytoward the torque converter end of the transmission. Then pull the lever back two notches fromPark through Reverse to the Neutral position. Set the selector level to the Neutral position andtighten the swivel nut while holding the lever lightly toward the reverse position.

Check Idle Speed and Adjust if Applicable

Idle speed is an important aspect for transmission engagement. If set too high, when shiftingfrom neutral to drive or reverse, the engagement will be too abrupt, causing not only driver discomfort, but also affecting the components of the transmission as well. And, of course, if theidle is too low, it may cause the engine to stall or idle roughly.

To adjust the idle speed:

• The engine should be at operating temperature.

• All accessories should be off.

• Set the parking brake.

• Place the transmission in park or neutral position.

• Engine cooling fan should be off.





DiagnosisDuring diagnosis, always verify the customer complaint. If the verification includes a test drive,be sure to check the level of ATF first. This will ensure that a low level is not contributing to the

problem and give you an idea as to the condition and service that the vehicle has seen. Although preliminary checks suggest making adjustments, drive the vehicle before anyadjustments in order to experience the same condition as the customer. If you are unable toverify the problem, ask the customer to accompany you on the test drive and point-out when thecondition occurs.

When test driving a vehicle, have a plan and record your findings. The chart that follows is quitethorough and provides room for comments. Rather than trying to remember the results of aspecific test, simply refer to the diagnostic form. Not only do you want to find out what has failed,but also what is functioning properly. Armed with this information, you will save time in your diagnosis and be more thorough.





Road Test - Automatic Transmission





For example, if the transmission does not slip while accelerating from a stop with wide openthrottle, line pressure is sufficient. If shift points occur at the proper speeds, throttle pressure

and governor pressure are sufficient. Or for ECT transmissions, throttle sensor and speedsensor inputs are being received by the ECU and the circuit and solenoids are workingproperly.

Upshift quality is important to consider during the road test because it is an indicator of proper line pressure and accumulator operation. If all upshifts are harsh, it indicates a commonproblem such as line pressure and should be verified with a pressure test. If a harsh upshift isevident in a specific gear, check the accumulator which is associated with the holding device for that specific gear.

Following the road test, compare your findings with the troubleshooting matrix chart in the repair

manual. (An example can be found on page 15.) The matrix chart will assist you in identifyingcomponents or circuits which can be repaired while the transmission is mounted in the vehicle.Or identify the components which should be inspected with the transmission on the bench.

Based on your diagnosis, if the transmission can be repaired with an on vehicle repair, the off-vehicle repair should be attempted first. Should the transmission require removal from thevehicle, a remanufactured transmission should be evaluated against the cost of an in-houseoverhaul.

Electrical Diagnostic Testing

Onboard Diagnostics

The ECU is equipped with a built-in self diagnostic system, which monitors the speed sensors,solenoid valves and their electrical circuitry. If the ECU senses a malfunction:

1. It blinks the OD OFF light to warn the driver.

2. It stores the malfunction code in its memory.

3. (When properly accessed) it will output a diagnostic code indicating the faulty componentor circuit.





Once a malfunction is stored in the memory system, it will be retained until canceled (erased).The vehicle battery constantly supplies 12 volts to the ECU B terminal to maintain memory evenif the ignition switch is turned off. If the malfunction is repaired or returns to normal operation,

the warning light will go off but the malfunction code will remain in memory. In order to erase adiagnostic code from the memory, a specified fuse must be removed for approximately 30seconds with the ignition switch is off. The fuse is identified in the repair manual or on the ECTDiagnostic Information technician reference card.

Throttle Position Sensor Signal

In order to determine if the throttle position sensor signal and brake switch signal are beingreceived by the ECU, place the ignition switch to the ON position with the engine off, connect adigital voltmeter to the diagnostic check connector and slowly depress the throttle. On modelsprior to 1987, if the vehicle does not have a diagnostic check connector in the enginecompartment, connect the voltmeter to the DG Terminal. Its location can be found in the

appropriate repair manual.

The ECT terminal can be designated as TT or T1 depending on the vehicle model. The positionin the diagnostic check connector remains the same. The voltage will increase in one voltincrements from 1 to 8 volts as the throttle is slowly opened. To verify the brake signal, apply thebrake pedal while the throttle is wide open. The voltage displayed on the voltmeter screen willgo to zero.

If the voltage readings progress in a step-like fashion, it indicates proper operation of thefollowing:

• Throttle sensor • Circuit integrity from the sensor to the ECU• Circuit integrity from the ECU to the diagnostic check connector.





If the voltage remains at 0 volts as the accelerator is depressed, possible causes are:

• Brake signal remains on.

• IDL signal remains on.

• ECU power supply circuit.

• Faulty ECU.

The voltage chart above provides a voltage value for the corresponding throttle opening. Thiscan be used to establish accelerator position for a given throttle opening.





Terminal Voltage and Gear Position

To check for shift timing while the vehicle is driven, connect a voltmeter and drive the vehicle.Voltage will increase in one volt increments from 0 to 7 volts. These voltage signals are output

from the ECU to indicate a response to system sensors. The lock-up voltages in second andthird gear may not be consistently output with throttle opening under 50%. In order to outputeach voltage signal, the throttle will need to be open greater than 50%. If the gears fail to shift inresponse to the changes in voltage readings, the solenoids may be sticking or the electricalcircuit to the solenoid may have an open.





ECT Analyzer

The ECT Analyzer is designed to determine if a transmission malfunction is ECU/electrical

circuit related or in the transmission. The analyzer is connected at the solenoid electricalconnector using appropriate adapter harnesses. The vehicle is driven using the analyzer to shiftthe transmission.

If the transmission operates properly with the ECT Analyzer, the fault lies between the solenoidconnectors up to and including the ECU. On the other hand, if the transmission does notoperate properly with the analyzer, the fault is likely to be in the transmission. This wouldinclude a failure of the solenoid or a mechanical failure of the transmission. A solenoid maytest out electrically and fail mechanically because the valve sticks. Apply air pressure to thesolenoid; air should escape when the solenoid is energized and should not escape when thesolenoid is not energized.

Operating Instructions

Two technicians are required when testing with the ECT Analyzer. One technician must actuallydrive the vehicle, and the second technician will change gears.

CAUTION

The analyzer leads should be routed away from hot or moving engine components to avoiddamage to the tester.

Choose a safe test area where there are no pedestrians, traffic and obstructions.





Testing for proper gear shifting:

1. The driver and passengers should wear seat belts.

2. Depress the service brake pedal.

3. Start the engine and move the vehicle gear selector to Drive.

4. Rotate the gear selector knob on the ECT Analyzer to the "1-2" position. The transmission will shift tosecond gear.

5. Press and hold the first gear button. The transmission will shift to first gear.

6. Release the parking brake.

7. Accelerate to 10 mph.

8. Release the first gear button. The transmission should shift to second gear.


10. Rotate the selector knob to the number "T' position. The transmission should shift into third gear.


12. Rotate the selector knob to the number "4" position. The transmission should shift to fourth gear.

13. Release the accelerator and coast.

14. Rotate the selector knob to the number "T' position. The transmission should downshift into third gear.

15. Apply the brakes, and stop the vehicle. Testing is complete.

Testing for lockup operation:

1. Operate the vehicle and ECT Analyzer up to fourth gear.


3. Press and hold the "Lockup" button to engage the lockup clutch. Observe the tachometer and note aslight reduction in the engine rpm. (Is more noticeable when the vehicle is going up a slight hill due to

converter slippage.)

4. Release the "Lockup" button to disengage the lockup clutch.

5. Apply vehicle brakes, and bring the vehicle to a halt. Test is complete.

Note: Testing for lockup can also be performed with the vehicle stopped, but with the engine running, With thegear shift selector in "D," press the "Lockup" button to engage the lockup clutch. With the converter inlockup, the engine idle rpm will drop significantly or stall. If there is no change 'in the engine idle rpm, thelockup function is not operational.





ASSIGNMENT NAME:_______________________________

1. What components replaced governor and throttle pressure signals in an ECTtransmission?

2. How may solenoids are used in a current model ECT transmission. Please

state the function (control) of each?

3. Explain the procedure of how to pull and read a transmission trouble code?

4. Explain the procedure of how to separate between a mechanical and/or anelectrical problem in an ECT transmission.

5. How many speed sensors are used on a vehicle with an ECT transmission,state location, correct I.D. (name) of each sensor, and which is the primaryinput to the ECT computer.

6. Explain the procedure for checking ECT speed sensors.

7. Explain the construction and operation of the ECT speed senor.

8. List all inputs used by the ECT computer and the need for each?

9. Explain the construction and operation of the direct TPS (linear) in

relationship to an indirect TPS in an ECT transmission?

10.Explain which ECT diagnostic checks can be made from the Diagnosticconnector?

11.Explain the conditions that must occur in order for converter lockup to occur in anECT transmission.

12.Explain the relationship that the brake switch, cruise control, and coolanttemperature sensor (THW) have in common with torque converter lockup.

13.Explain how solenoids can be checked on the car.





SHIFT INTERLOCK SYSTEM

The shift lock system is designed to ensure the proper operation of the automatictransmission. The driver must depress the brake pedal in order to move the gear selector from

Park to any other range. In addition, the ignition key cannot be turned to the Lock position andremoved from the ignition switch unless the gear selector is placed in the Park position.

There are three systems available in Toyota models; electrical, electrical/ mechanical andmechanical. We will not cover the application by model but rather by system type. For thespecifics on a particular model, consult the repair manual.





Electrical Shift Lock TypeThe electrical type uses electrical control of the shift lock mechanism, as well as the key lockmechanism.

Shift Lock Mechanism

The shift lock mechanism is made up of a number of components as seen in the illustrationbelow.

The shift position switch (shift lock control switch) is used to detect the position of the shift lever.

It has two contacts, P1 and P2. When the select lever is in the Park position, P1 is on (closed)and P2 is off (open). In this position, the key can be removed but the select lever is locked inposition.

When the select lever is in a position other than Park, P1 is off (open) and P2 is on (closed). Inthis position, the key cannot be removed.

The grooved pin is part of the normal detent mechanism which requires that the shift lever button be depressed in order to move the gear selector into and out of Park position and alsointo Manual 2 or Manual Low positions. The shift lock plate is mounted next to the detent plate.In the Park position, the grooved pin fits into the slot at the top of the shift plate. The shift lock

plate movement is limited by the plate stopper when the solenoid is not energized.





Shift Lock Override Button

In order to move the shift lever out of Park, the ignition switch must be in the Accessory or ONposition and the brake pedal must be depressed. When the brake pedal is depressed, theECU turns on the solenoid, moving the plate stopper and allowing the shift lock plate to movedown with the grooved pin.

If the shift lock solenoid becomes inoperative, the shift lever cannot be moved and the vehiclecannot be moved. The shift lock override button can be used to release the plate stopper fromthe shift lock plate, releasing the shift lever so it can be moved from the Park position.

Shift Lock ECU

The ECU is generally found near the shift select lever. The shift lock system computer controls

operation of the key lock solenoid and the shift lock solenoid based on signals from the shiftposition switch and the stop light switch.





Key Interlock System

A camshaft is provided at the end of the key cylinder rotor. This camshaft has a cam with thecut-out portion of its stroke from the ACC position to the ON or Start position. The pin of the key

lock solenoid protrudes out against the cam when the current is on and is pulled back by thereturn spring when the current is off.

When the shift lever is shifted to a range other than the P range, current flows from thecomputer to the key lock solenoid, causing the pin to protrude out. If the key cylinder is turnedwith the pin in this position, it can be turned to the ACC position but cannot be turned further,due to the pin pushing against the cam. This prevents the key cylinder from being turned to theLock position.

The current to the key lock solenoid is cut off when the shift lever is shifted to the P range andthe pin is pulled back by the return spring. This allows the key cylinder to be turned to the Lock

position, and the key can be removed.

Shift Lock System Computer

The shift lock system computer controls operation of the key lock solenoid and the shift locksolenoid based on signals from the shift position switch and the stop fight switch.

Key Lock Solenoid Control

The shift position switch P2 is on (closed) when the shift lever is in a range other than the Parkrange. Current from the ACC and ON terminals of the ignition switch flows to Tr2 through thetimer circuit. The base circuit of Tr2 is grounded by switch P2, and Tr2 goes on, energizing thekey lock solenoid, preventing the key from going to the Lock position. The timer circuit cuts off

the flow of current to Tr2 approximately one hour after the ignition switch is turned from ON to ACC, switching off the key lock solenoid. The timer circuit prevents the battery from beingdischarged.

By placing the gear selector in the Park position, switch P2 is off (open), current no longer flowsto the base of Tr2 and it goes off. The solenoid is no longer energized, and the solenoidplunger is retracted, and the key can be removed.





Shift Lock Solenoid Control

When the shift lever is in the Park range, shift position switch P1 is on and the emitter circuit of Tr3 is grounded. Base current for Tr3 is provided through the stop light switch which is openwhile the brake is not applied, so Tr3 is off. Tr3 controls the base of Tr1, and as long as Tr3 isoff, the shift lock solenoid will remain off and the gear selector will be locked in the Parkposition.

When the brake pedal is depressed, the stop light switch goes on, providing current to the base

of Tr3. When Tr3 goes on, base current flows in Tr1 and it then goes on, causing current to flowto the shift lock solenoid and freeing the shift lever. When the shift lever is shifted out of Park,the shift position switch P1 goes off and Tr1 switches the shift lock solenoid off.





Electrical / Mechanical Shift Lock TypeThe electrical/mechanical type uses electrical control of the shift lock mechanism and amechanical control of the key lock mechanism.

Key Interlock Device

Similar to the construction discussed previously, a camshaft is provided at the end of the keycylinder rotor. This camshaft has a cam with the cut-out portion of its stroke from the ACCposition to the ON or Start position. The lock pin is attached to the end of the parking lock cableand slides with the movement of the control lever mounted to the shift lever mechanism. Thecontrol lever is separate from the shift lock plate but is actuated by it.

Notice the crank ditch sloth in the shift lock plate. It is cut at an angle so that when the shift lockplate moves up or down, it causes the control lever to pivot at point B in the illustration below.

When the shift lever is in the Park position, the control lever rotates around B counterclockwise,pushing the parking lock cable so that the lock pin does not interfere with the camshaft. In thisposition, the key can be turned to the Lock position and removed.

When the shift lever is moved from the Park position, the lock plate is pushed downward by theshift lever button and the grooved pin. When the shift lock plate moves downward the controllever rotates clockwise, pulling the parking lock cable and lock pin into engagement with thecamshaft. In this position, the key cannot be turned to the Lock position and removed from the

ignition as seen in the following illustration.





Mechanical Shift Lock Type

The mechanical type uses mechanical control of the shift lock mechanism and the key lockmechanism. A cable extends from the brake pedal bracket to the shift lever control shaftbracket. A lock pin engages the shift lever shaft to lock in into the Park position until the brakesare applied.

The cable (wire) end on the brake pedal bracket is mounted just below the stop light switch.The plunger is attached to the cable and is mounted in a wire guide and is able to slide in andout. When the brake pedal is not depressed, the plunger is held in position by the brake pedalreturn spring.

The other end of the cable is attached to a lock pin located in the shift lever control shaft bracket.The lock pin is spring loaded to release the lock pin from the inner shaft of the shift lever.





When the shift lever is in the Park range and brakes are not applied, the cable compresses theNo. 1 return spring and pushes the lock pin engaging the round hole in the inner shaft, lockingthe shift lever in Park

When the brakes are applied with the transmission in Park, the No. 1 spring pushes the cable,lock pin and plunger out toward the brake pedal. With the plunger released, the shift lever canbe moved from Park.

When the shift lever is in positions other than Park with the brakes released, the brake pedalreturn spring pushes the plunger and cable back toward the shift lever control shaft. The lockpin cannot enter the inner shaft, so the No. 2 return spring compresses. With the lock pin springloaded, when the gear selector is moved to the Park position, it will immediately lock.

Reprinted with permission by Toyota Motor Sales, USA, Inc.,from the Automatic Transmission Course #262 textbook.





Electronic Fuel Injection Overview

How Electronic Fuel InjectionWorks

Electronic Fuel injection works on the somevery basic principles. The followingdiscussion broadly outlines how a basic or Convention Electronic Fuel Injection (EFI)

system operates.

The Electronic Fuel Injection system can bedivided into three: basic sub-systems. Theseare the fuel delivery system, air inductionsystem, and the electronic control system.

EFI #1 - SYSTEM OVERVIEW




The Fuel Delivery System

• The fuel delivery system consists of thefuel tank, fuel pump, fuel filter, fuel deliverypipe (fuel rail), fuel injector, fuel pressureregulator, and fuel return pipe.

• Fuel is delivered from the tank to theinjector by means of an electric fuel pump.The pump is typically located in or near the

fuel tank. Contaminants are filtered out by ahigh capacity in line fuel filter.

• Fuel is maintained at a constant pressureby means of a fuel pressure regulator. Anyfuel which is not delivered to the intakemanifold by the injector is returned to thetank through a fuel return pipe.





The Air Induction System

• The air induction system consists of the air cleaner, air flow meter, throttle valve, air intake chamber, intake manifold runner,and intake valve.

• When the throttle valve is opened, air flowsthrough the air cleaner, through the air flowmeter (on L type systems), past the throttlevalve, and through a well tuned intakemanifold runner to the intake valve.

• Air delivered to the engine is a function of driver demand. As the throttle valve isopened further, more air is allowed to enter the engine cylinders.

• Toyota engines use two different methodsto measure intake air volume. The L typeEFI system measures air flow directly byusing an air flow meter. The D type EFIsystem measures air flow indirectly by

monitoring the pressure in the intakemanifold.





Electronic Control System

• The electronic control system consists of various engine sensors, Electronic ControlUnit (ECU), fuel injector assemblies, andrelated wiring.

• The ECU determines precisely how muchfuel needs to be delivered by the injector bymonitoring the engine sensors.

• The ECU turns the injectors on for aprecise amount of time, referred to as

injection pulse width or injection duration,to deliver the proper air/fuel ratio to theengine.





Basic System Operation

• Air enters the engine through the air induction system where it is measured by

the air flow meter. As the air flows into thecylinder, fuel is mixed into the air by the fuelinjector.

• Fuel injectors are arranged in the intakemanifold behind each intake valve. Theinjectors are electrical solenoids which areoperated by the ECU.

• The ECU pulses the injector by switchingthe injector ground circuit on and off.

• When the injector is turned on, it opens,spraying atomized fuel at the back side of the intake valve.

• As fuel is sprayed into the intake airstream,it mixes with the incoming air and vaporizesdue to the low pressures in the intakemanifold. The ECU signals the injector todeliver just enough fuel to achieve an idealair/fuel ratio of 14.7:1, often referred to asstoichiometry.

• The precise amount of fuel delivered to theengine is a function of ECU control.

• The ECU determines the basic injectionquantity based upon measured intake air

volume and engine rpm.

• Depending on engine operating conditions,injection quantity will vary. The ECUmonitors variables such as coolanttemperature, engine speed, throttle angle,and exhaust oxygen content and makesinjection corrections which determine finalinjection quantity.





Advantages of EFI

Uniform Air/Fuel Mixture Distribution

Each cylinder has its own injector whichdelivers fuel directly to the intake valve. Thiseliminates the need for fuel to travel throughthe intake manifold, improving cylinder tocylinder distribution.

Highly Accurate Air/Fuel Ratio ControlThroughout All Engine Operating Conditions EFI supplies a continuously accurate air/fuelratio to the engine no matter what operatingconditions are encountered. This providesbetter driveability, fuel economy, andemissions control.

Superior Throttle Response and Power

By delivering fuel directly at the back of theintake valve, the intake manifold design canbe optimized to improve air velocity at theintake valve. This improves torque andthrottle response.

Excellent Fuel Economy WithImproved Emissions Control

Cold engine and wide open throttleenrichment can be reduced with an EFIengine because fuel puddling in the intakemanifold is not a problem. This results inbetter overall fuel economy and improvedemissions control.

Improved Cold EngineStartability and Operation

The combination of better fuel atomizationand injection directly at the intake valveimproves ability to start and run a coldengine.

Simpler Mechanics,Reduced Adjustment Sensitivity

The EFI system does not rely on any major adjustments for cold enrichment or fuelmetering. Because the system ismechanically simple, maintenancerequirements are reduced.





EFI/TCCS System

With the introduction of the Toyota Computer Control System (TCCS), the EFI system wentfrom a simple fuel control system to a fullyintegrated engine and emissionsmanagement system. Although the fueldelivery system operates the same asConventional EFI, the

Ignition Spark Management (ESA)

The EFI/'TCCS system regulates sparkadvance angle by monitoring engineoperating conditions, calculating theoptimum spark timing, and firing the spark

plug at the appropriate time.

Idle Speed Control (ISC)

The EFI/TCCS system regulates engine idlespeed by means of several different types of ECU controlled devices. The ECU monitorsengine operating conditions to determinewhich idle speed strategy to use.

TCCS Electronic Control Unit (ECU) alsocontrols ignition spark angle. Additionally,TCCS also regulates an Idle Speed Controldevice, an Exhaust Gas Recirculation (EGR)Vacuum Switching Valve and, depending onapplication, other engine related systems.

Exhaust Gas Recirculation (EGR)

The EFI/TCCS system regulates the periodsunder which EGR can be introduced to theengine. This control is accomplished throughthe use of an EGR Vacuum Switching Valve.

Other Engine Related Systems

In addition to the major systems justdescribed, the TCCS ECU often operates anElectronically Controlled Transmission(ECT), a Variable Induction System (T-VIS),the air conditioner compressor clutch, andthe turbocharger/supercharger.





Self Diagnosis System

A self diagnosis system is incorporated intoall TCCS Electronic Control Units (ECUs)and into some Conventional EFI systemECUs. A Conventional EFI engine equippedwith self diagnostics is a P7/EFI system.This diagnostic system uses a check enginewarning lamp in the combination meter which is capable of warning the driver whenspecific faults are detected in the enginecontrol system. The check engine light is

also capable of flashing a series of diagnosis codes to assist the technician introubleshooting these faults.

Summary

The Electronic Fuel Injection systemconsists of three basic subsystems.

• The electronic control system determinesbasic injection quantity based upon

electrical signals from the air flow meter and engine rpm.

• The fuel delivery system maintains aconstant fuel pressure on the injector. Thisallows the ECU to control the fuel injectionduration and deliver the appropriateamount of fuel for engine operatingconditions.

• The air induction system delivers air to theengine based on driver demand. Theair/fuel mixture is formed in the intakemanifold as air moves through the intakerunners.

The EFI system allows for improved engineperformance, better fuel economy, andimproved emissions control. Althoughtechnologically advanced, the EFI system is

mechanically simpler than other fuelmetering systems and requires very littlemaintenance or periodic adjustment.

• The Conventional EFI system only controlsfuel delivery and injection quantity. 'Meintroduction of EFI/TCCS added control Of Electronic Spark Advance, idle speed, EGR,and other related engine systems.

• Most of Toyota's late model EFI systems

are equipped with some type of on boarddiagnosis system. All TCCS systems areequipped with an advanced self diagnosissystem capable of monitoring manyimportant engine electrical circuits. Onlysome of the later productionConventional(P7) EFI engines areequipped with a self diagnosis system.

Reprinted with permission from Toyota Motor Sale,U.S.A., Inc. from #850 EFI Course Book.





Overview Of TheAir Induction System

The purpose of the air induction system is tofilter, meter, and measure intake air flow intothe engine. Air, filtered by the air cleaner,passes into the intake manifold in varyingvolumes. The amount of air entering theengine is a function of throttle valve openingangle and engine rpm. Air velocity isincreased as it passes through the long,narrow intake manifold runners, resulting inimproved engine volumetric efficiency.

Intake air volume is measured by movementof the air flow meter measuring plate or bydetecting vortex frequency on enginesequipped

with L type EFI. On engines equipped withD type EFI, air volume is measured bymonitoring the pressure in the intakemanifold, a value which varies proportionallywith the volume of air entering the engine.

The throttle valve directly controls the volumeof air which enters the engine based ondriver demand. Additionally, when the engineis cold, it is necessary for supplementary air

to by-pass the closed throttle valve to providecold fast idle. This is accomplished by a bi-metallic or wax type air valve or by an ECUcontrolled Idle Speed Control Valve (ISCV).

EFI #2 - A IR INDUCTION SYSTEM




Air InductionSystem Components

Vane Air Flow Meter (L Type EFI)

The vane type air flow meter is a commonlyused air volume measurement device onToyota EFI engines. The meter consists of ameasuring plate, which is spring loadedclosed by a return spring, and apotentiometer attached to the plate, whichvaries an electrical signal to the ECU as theposition of the plate changes. Air volumeentering the engine is directly proportional tothe amount of movement detected from themeasuring plate. Additionally, the air flow

meter incorporates a fuel pump enablecontact which breaks the ground circuit of thecircuit opening relay if the engine stopsrunning.

The air flow meter is placed in seriesbetween the air cleaner and the throttle body,thereby measuring all air which enters theengine. Integrated with the air flow meter isan intake air temperature sensor and an idlemixture by-pass passage.

Idle Mixture Air By-pass Circuit

For proper calibration of the engine air/fuelratio at idle speed, an idle mixture air by-passcircuit is incorporated into the air flow meter.

A screw is used to adjust the amount of air which by-passes the measuring plate. Thisscrew is adjusted and sealed at the factory todiscourage improper adjustment andtampering. There are no provisions or specifications for field adjustment.

After factory calibration of the air flow meter, atwo-digit number is stamped into the meter casting near the idle mixture adjusting screw.This number indicates the distance from the

casting to the flat surface of the screw andcan be used as a reference if the idle mixturescrew has been tampered with.

The calibration number can be interpreted byreferring to the examples in the followingchart.





Fuel Pump Circuit Control A fuel pump switch is incorporated into theair flow meter to prevent the fuel pump fromrunning unless the engine is running. Anymovement of the air flow meter measuringplate will cause the fuel pump switch contactto close. When the engine is not running, themeasuring plate forces the fuel pump switchcontact open, preventing the circuit openingrelay from operating. For more informationon the fuel pump electrical circuit, refer tosection 3, "Fuel Delivery and InjectionControl."

Karman Vortex Air Flow Meter (L Type EFI)

The Karman vortex air flow meter is usedonly on limited applications (7M-GTE andLexus 1UZ-FE & 2JZ-GE engines). Themeter is smaller and lighter than the vanetype meter and offers less resistance toincoming air flow.

The sensor operates on the principle of measuring the vortices created as air flowspast a pillar shaped vortex generator. Thefrequency with which these vortices arecreated increases in direct proportion to the

amount of air flowing across the vortexgenerator. Vortex frequency is detected by aphotocoupler and converted into a variablefrequency digital signal by the sensor. Anintake air temperature sensor is alsoincorporated into the Karman vortex air flowmeter. For more information about operationof this air flow meter and its signals , refer tosection 5, "Electronic Engine Controls."

Throttle Body

The throttle body consists of the throttle valve,the idle air by-pass circuit, the throttleposition sensor, and also houses variousported and manifold vacuum sources tooperate emissions devices. Throttle icing isprevented by use of an engine coolant cavitylocated adjacent to the throttle valve.





Idle Air By-pass

During idle operation, the throttle valve isalmost completely closed. Idle air enters theengine through an adjustable throttle air by-pass screw which varies the amount of air which can flow past the closed throttle valve.By turning this screw clockwise, throttlebypass air is reduced, causing a decrease inidle speed. Conversely, turning the screwcounterclockwise will increase idle speed by

allowing more air to pass the closed throttlevalve.

On engines equipped with an ECUcontrolled ISCV, this throttle air by-passscrew is seated at the factory, and there areno provisions for curb idle adjustment. Idleair is varied by the ECU through control of theISC Valve position.

Decel Dashpot and ThrottleOpener Systems

A decel dashpot or throttle opener ismounted to the throttle body on someengines. The decel dashpot is designed to

keep the throttle valve from closing toosuddenly during deceleration. The throttleopener is designed to hold the throttle valveopen slightly after the engine is turned off.

Non ECU Controlled Throttle Opener Starting with 1990 3S-FE and 5S-FE engines,a simple throttle opener diaphragm was

added to the throttle body. The throttle opener diaphragm is spring loaded in the extendedposition, holding the throttle valve openslightly when vacuum is not applied to thediaphragm. When the engine is started,manifold vacuum from the TO port retractsthe throttle opener for normal curb idle.

The intent of the throttle opener system is tokeep the throttle valve slightly open after theengine is turned off.

Non-ECU Controlled Dashpot On someengines, a simple dashpot is used. Whenthe throttle is open, the dashpot diaphragmspring extends the control rod, allowingatmospheric pressure to enter thediaphragm chamber through a small bleedrestriction (VTV).





When the throttle closes, the throttle returnspring pushes the dashpot control rodtoward the retracted position. Atmospheric

pressure trapped in the diaphragm chamber slowly bleeds through the restriction,causing the throttle to close slowly.

ECU Controlled CombinationThrottle Opener/Dashpot

Dashpot and throttle opener functions arecombined into one ECU controlled systemon some late model engines like the '91 3E-E. This system uses an ECU controlled VSVto switch vacuum to the throttle

opener/dashpot diaphragm.

• When the engine is stopped, springtension extends the control rod, causingthe throttle to open.

• When the engine is running above a given

rpm, the ECU energizes the VSV, allowingatmospheric pressure to bleed into thethrottle opener/dashpot diaphragm throughthe Vacuum Transmitting Valve (VTV). Thisallows spring tension to extend the controlrod.

• When the throttle angle closes beyond aspecified point during deceleration, theECU de-energizes the VSV, allowingmanifold vacuum to bleed through the VTVand act on the diaphragm. This causes thecontrol rod to gradually retract, slowlyclosing the throttle valve.

The idle air by-pass screw, dashpot, andthrottle opener do not require routineadjustment. In the event that thesecomponents have been tampered with, refer to the appropriate repair manual for adjustment procedures of curb idle, dashpot,throttle opener, and A/C idle up.

• ECU turns VSV ON as throttle opens; rodextends

• ECU turns VSV OFF on deceleration; rodallows throttle to close slowly

• Engine OFF; rod extends, holding throttleopen slightly





Air Valves

There are two types of non-ECU controlledair valves used on some engines to controlcold engine fast idle. These valves, theelectrically heated bi-metal type and the

coolant heated wax type, vary the amount of air bypassing the closed throttle valve duringcold engine operation.

Bi-metal Type Air Valve

This gate valve operates on the principle of aspring loaded gate balanced against a bi-metal element. The tension of the bi-metallicelement varies the position of the gate as its

temperature changes. The bi-metal elementis heated by an electrical heater coil and bythe temperature of the ambient air surrounding it. The air valve assembly isinstalled on the surface of the cylinder headto keep the gate valve closed during hot soakperiods.





Heater current for the air valve is supplied bythe circuit opening relay power contact, thesame circuit which feeds the fuel pump.

Air valve operation can be quick checked bypinching off a supply hose and observing therpm drop. When checked with a warmengine, the drop should be less than 50 rpm.When the engine is cold, the rpm drop

should be high.





Wax Type Air Valve

The wax type air valve is integrated with thethrottle body and varies an idle air by-passopening as coolant temperature changes.The valve works on the principle of a spring

loaded gate valve balanced against a coolantheated, wax filled thermo valve.

When coolant temperature is cold, the waxfilled thermo valve retracts allowing spring Ato push the gate valve open. This allows air

to flow from the air cleaner side of the valveto the intake side of the valve.

As coolant temperature rises, the wax filledthermo valve expands allowing spring B togradually close the valve (spring B is stronger than spring A). This causes engine rpm todecrease as air flow to the intake is

decreased.

The wax type air valve should be fully closedby the time engine coolant temperaturereaches approximately 80'C (176'F).

• Cold engine, large rpm drop• Fully warmed engine!~100 rpm drop





A good quick check for the wax type air valveis to observe engine rpm throughout thewarm up cycle. Look for high rpm upon initialstartup and gradual reduction to normal curbidle speed as the engine reaches normal

operating temperature.

On D type EFI, the valve operation can alsobe checked by removing the air inlet pipe atthe throttle body and blocking the fresh air port inside the throttle bore. When the engineis cold, engine rpm should drop greater than100 rpm. Once the engine reaches normaloperating temperature (~~ 176'F), rpm dropshould not exceed 100 rpm.

Intake Air Chamber & Manifold

Port delivered Electronic Fuel Injectionsystems offer the advantage of not having tomove fuel through the intake manifold. Thisallows for improved performance andemissions through optimum design of theintake air chamber and manifolds.

A large intake air chamber is provided toeliminate pulsation, thereby improving air distribution to each manifold runner. Long,narrow manifold runners are branched off toeach intake port to improve air velocity at the

intake valve. This design offers the followingbenefits:

• Fuel puddling is eliminated, providing for leaner cold engine and power air/fuelratios. This equates to reductions inemissions and improved fuel economy.

• Volumetric efficiency of the engine isimproved, thereby improving engine torqueand horsepower.

Depending upon application, the intake air chamber and manifolds may be integrated or separate. Some Toyota engines utilize anECU controlled variable induction systemwhich optimizes manifold design for low andhigh speed engine operation. For moreinformation on these systems, refer to "Other TCCS Related Systems."





Manifold Absolute PressureSensor (D Type EFI)The D type EFI system eliminates the use of an air flow meter and uses a manifold

absolute pressure sensor as a loadmeasurement device instead.

Because pressure in the intake manifold isproportional to the amount of air entering it,the manifold absolute pressure sensor isused to measure air intake volume in the Dtype EFI system.

This sensor compares a variable pressureinside the intake manifold with a fixed

reference pressure inside the sensor. A totalvacuum chamber is placed on one side of apiezo-resistive silicon chip; manifoldpressure is applied to the other side of thechip. As the chip flexes, the mechanicalmovement is converted into a variable voltagesignal by the sensor. There are severaldifferent names used in reference to theManifold Absolute Pressure sensor,depending on the publication you read. Twoother common names used to refer to this

sensor are PIM, or Pressure Intake Manifold,and Vacuum sensor.

For more information about operation of themanifold absolute pressure sensor and itssignal characteristics, refer to "ElectronicEngine Controls."





Idle-Up Systems

Air Conditioning Idle-up

The air conditioning idle-up system is usedto increase engine idle rpm any time the air conditioning compressor is in operation. Thesystem shown is used on D type EFIapplications where the ECU controlled IdleSpeed Control Valve (ISCV) does not have an

A/C idle-up feature. This system maintainsengine idle stability during periods of A/Ccompressor operation. Additionally, it keepscompressor speed sufficiently high toensure adequate cooling capacity at idlespeed.

The A/C idle-up system consists of an A/Camplifier controlled Vacuum Switching Valve(VSV) and an Air Switching Valve (ASV) or actuator. By applying vacuum to the ASVdiaphragm, fresh air from the air cleaner isby-passed into the intake manifold,increasing engine rpm.

When the VSV is energized, a manifoldvacuum signal is applied to the actuator diaphragm of the ASV causing it to open thepassage between the fresh air supply andthe intake manifold. This extra air introduceddirectly into the intake manifold causesengine rpm to increase.

When the VSV is de-energized, the vacuumcontrol signal to the ASV is blocked and anytrapped vacuum is bled off of the diaphragm.This causes the ASV to block air flowing tothe intake manifold, decreasing rpm.

The A/C idle-up system described above isnot an ECU controlled system. For information on ECU controlled ISCV systemswhich control A/C idle-up speed, refer to"Engine Controls - Idle Speed ControlSystems."





Power Steering Idle-upThe power steering system draws asignificant amount of horsepower from theengine when the steering wheel is turned toeither stop. This can have an adverse effecton vehicle driveability. To address thispotential problem, many EFI enginesequipped with power steering use a power steering idle-up system which activateswhenever the steering wheel is turned to astop.

The power steering idle-up system consistsof a hydraulically operated air control valveand a vacuum circuit which by-passes thethrottle valve. Whenever power steeringpressure exceeds the calibration point of thecontrol valve, the valve opens, allowing acalibrated volume of air to by-pass the closedthrottle valve.

Because power steering pressure onlyexceeds the pressure calibration point of thevalve when the steering wheel is turned to itsstop, the system is only functional during verylow speed maneuvering and at idle. Thesystem can be tested by turning the steeringwheel to a stop while listening for an rpmincrease.





Common ServiceConcerns and Solutions

During service procedures, there are two

concerns related to the air induction systemwhich the technician should be aware of.These are false or unmeasured air entry intothe intake system and deposit buildup on theback side of intake valves.

False air is any air which enters the inductionsystem unwanted and/or unmeasured. Inaddition to obvious leaks in the intakemanifold, with an L type EFI system, false air can enter the induction system through theconnecting pipe between the air flow meter and the throttle body as well as through

leaks into the crankcase. Because this air isable to enter the intake manifoldunmeasured, the result is an excessivelylean air/fuel ratio. The end result of false air with L type EFI is rough idle, stumble, and/or flat spots.

With the D type EFI system, false air is

typically measured by the EFI systembecause it results in an increase in manifoldabsolute pressure. The end result is anengine that idles excessively high but with arelatively normal air/fuel mixture.

There are several tests which can detectfalse air entry into the induction system. Agood visual inspection of the intake air connector pipe and connection points as wellas inspection of all vacuum hoses, engine oil

filler cap, and dip stick seals are a must.

If this fails to identify a suspected leak,spraying carburetor cleaner aroundsuspected leak areas while observing aninfrared exhaust analyzer for carbonmonoxide increase is another method toassist in leak detection.

Another method to locate suspected false air entry points is to pressurize the intake

system with a regulated shop air supply(CAUTION: do not exceed 25 PSI). Spray asoapy water solution around all suspectedleak areas. Simply listen and observe for bubbles to locate leak sources. This methodrequires sealing the air cleaner fresh air inletand blocking the throttle valve open topressurize the intake air connector pipe. Theair pressure can be applied through anylarge manifold vacuum fitting.





This condition manifests itself as hardened

carbon deposits on the back side of theintake valves. It varies in degree dependingon the engine, fuel quality, and customer driving habits.

Intake valve deposits present a dualproblem. First, these deposits restrict theflow of air and fuel mixture into the cylinder,reducing volumetric efficiency and potentiallyaffecting high rpm engine performance.

Additionally, these carbon deposits act like

sponges absorbing fuel vapor. This causeslean driveability problems, particularly duringcold engine operation.

The best way to identify this condition is bysymptom and then through visual inspection.

A visual inspection can be performed using aborescope, SSI #00451-42889, to confirmthe problem. The intake manifold can alsobe removed to confirm the existence and thedegree of this condition.

The accompanying chart will help you todetermine the appropriate action to takebased upon visual inspection. Visualinspection can be performed without removalof the cylinder head or intake manifold byusing a borescope, SSI 00451-42889. Theengine can be manually rotated until theintake valve is fully open; then the borescope

can be inserted through a spark plug hole for inspection.

Repairs can be affected by use of SST00002216401, a walnut shell type Carbon

Cleaner Kit, and 00002-217256, a UniversalPlate & Gasket Kit. These tools will allowremoval of deposits without removal of thecylinder head.

Summary In this chapter, you have learnedthat the air induction system filters, meters,and measures air flow into the engine. Byusing multiple port injection, the intakesystem can be designed with long tunedintake runners to improve the engine'svolumetric efficiency.

Air flow into the engine is controlled by thedriver by opening and closing the throttlevalve. As air enters the engine, it is measuredby one of three different types of air flowmeters with L type injection or by a manifoldabsolute pressure sensor with D typeinjection.

To improve engine idle quality during coldengine operation, some engines use amechanical air valve to control air flow pastthe closed throttle valve. There are twodifferent types of air valves used, one heatedby engine coolant, the other heatedelectrically.

Depending on engine application, there areseveral different types of throttle control andidle-up devices used. Throttle body mounted

devices provide a deceleration dashpotfunction and/or throttle opener function.Remotely mounted idle-up devices are usedon some engines to control additional air flow into the engine when load from the A/Ccompressor or power steering pump areplaced on the engine.

In section 3, Fuel Deliver & Injection controls,you will learn about the fuel delivery system.





Reprinted with permission from Toyota Motor Sale, U.S.A., Inc. from #850 EFI Course Book.





Overview of theFuel Delivery SystemThe fuel delivery system incorporates thefollowing components:

1) Fuel tank (with evaporative emissionscontrols)

2) Fuel pump3) Fuel pipe and in line filter 4) Fuel delivery pipe (fuel rail)5) Pulsation damper (many engines)6) Fuel injectors7) Cold start injector (most engines)8) Fuel pressure regulator 9) Fuel return pipe

Fuel is pumped from the tank by an electricfuel pump, which is controlled by the circuitopening relay. Fuel flows through the fuelfilter to the fuel rail (fuel delivery pipe) andup to the pressure regulator where it is heldunder pressure. The pressure regulator maintains fuel pressure in the rail at aspecified value above intake manifoldpressure. This maintains a constant

pressure drop across the fuel injectorsregardless of engine load. Fuel in excess of

that consumed by engine operation isreturned to the tank by way of the fuel returnline. A pulsation damper, mounted to the fuelrail, is used on some engines to absorbpressure variations in the fuel rail due toinjectors opening and closing.

The fuel injectors, which directly control fuelmetering to the intake manifold, are pulsedby the ECU. The ECU completes the injector ground circuit for a calculated amount of time

referred to as injection duration or injectionpulse width. The ECU determines whichair/fuel ratio the engine runs at based uponengine conditions monitored by inputsensors and a program stored in its memory.

During cold engine starting, many enginesincorporate a cold start injector designed toimprove startability below a specified coolanttemperature.

EFI #3 - FUEL DELIVERY & INJECTION CONTROL




Fuel Delivery andInjection Control Components

Fuel Pumps

Over the years, Toyota has used two types of electric fuel pumps on EFI systems. Theearly Conventional EFI system used anexternally mounted in-line pump. Theseroller cell pumps incorporate an integralpressure pulse damper or silencer designedto smooth out pressure pulses and providequiet operation.





Later model production engines utilize an in-tank pump integrated with the fuel sender unit. These turbine pumps operate with lessdischarge pulsation and run quieter than thein-line variety. In-tank pumps can be serviced

by removing the fuel sender unit from thetank. Make sure that the pump coupling hoseis in good condition prior to replacing thepump.

Both pumps share many features. They arereferred to as wet pumps because theelectric motor operates immersed in fuel.Passing fuel through the pump motor aids incooling and lubrication.

An outlet check valve is incorporated in thedischarge outlet to maintain residual or restpressure when the engine is turned off. Thisreduces the possibility of vapor-lock andimproves starting characteristics. A pressurerelief valve is used to prevent over-pressureand potential fuel leakage in the event thatpressure or return lines become restricted.





Fuel Pump Electrical Controlsand Circuit Opening Relay

Circuit Opening Relay Circuits There are

three types of fuel pump control circuits usedon Toyota's EFI engines. One type of control,

A second type of fuel pump control uses theECU to control circuit opening relay runwinding current. Used on engines equippedwith D type EFI and on the 7M-GTE, whichuses a Karman vortex air flow meter, this

used exclusively with L type injection, utilizes

the air flow meter Fc contact to complete thecircuit opening relay run winding ground. Thisis a safety feature which prevents the fuel

pump from operating when the engine is notrunning.

safety feature prevents fuel pump operationwhenever the ECU fails to see an Ne (enginerpm) signal. Under these conditions, theECU removes ground from the circuitopening relay run winding.





Fuel Pump Speed ControlThe third type of fuel pump control circuitutilizes a two-speed pump electrical circuit.Depending upon engine, the circuit openingrelay may be driven by the ECU or by the air flow meter Fc contact. Pump current,however, is supplied either through a currentlimiting resistor or directly to the pumpdepending on engine load, rpm and status of the STA signal.

When the engine is cranked, or operated athigh speed and/or heavy load, the ECU turnsoff TR1, closing contact A of the Fuel Pump

Control Relay. This allows current to flowdirectly to the fuel pump, causing it to run athigh speed.

Under all other operating conditions, the ECUturns on TR1, which energizes the FuelPump Control Relay. This closes relaycontact B and forces current to flow throughthe resistor, causing the pump to run at lowspeed. The Fuel Pump Speed Controlsystem is designed to reduce electricaldemand and pump wear when fuel demandis low while delivering adequate fuel volumewhen demand is high.





Fuel Pump Test TerminalsTo facilitate testing and allow pumpoperation independent of the air flow meter or ECU control, all engines utilize a fuelpump test connector.

There are two basic types of fuel pump testcircuits. Most late model TCCS engines usean Fp test terminal located in the checkconnector. With the ignition switch on,

jumpering +B to the Fp terminal sendscurrent-directly to the fuel pump.

Earlier engines use a jumper connector referred to as a 2P fuel pump checkconnector. This connector, when jumpered,supplies ground for the circuit opening relayrun winding, allowing it to operateindependently of the air flow meter Fc contact.





Fuel Filter

The fuel filter, which is installed between thepump and the fuel rail, removes dirt andcontaminants from the fuel before it isdelivered to the injectors and pressureregulator.

Although it is possible for the fuel filter tobecome contaminated or even completelyclogged, this is an unlikely conditionbecause of the high capacity and quality of Toyota's filter. This filter is considered to bemaintenance free and no service interval isrecommended for periodic replacement.

In the event that this filter becomes restrictiveto fuel flow, the engine will suffer fromsurging, loss of power under load and hardstarting problems. If it becomes necessary toreplace this filter there are some importantsafety matters to consider.

Fuel Delivery Pipe (Fuel Rail)The fuel delivery pipe, commonly referred toas a fuel rail, is designed to hold the injector in place on the intake manifold. Mounted tothe fuel delivery pipe are the pulsationdamper (when used) and the fuel pressureregulator. The fuel delivery pipe acts as areservoir for fuel which is held under pressure prior to delivery by the fuel injector.





Fuel Pressure Regulator The fuel pressure regulator is a diaphragmoperated pressure relief valve. To maintainprecise fuel metering, the fuel pressureregulator maintains a constant pressuredifferential across the fuel injector. Thismeans that the pressure in the fuel rail willalways be at a constant value abovemanifold absolute pressure.

The specified pressure differential is either 36 PSI (2.55 kg/CM2) or 41 PSI (2.90kg/CM2) depending on engine application.*Maintenance of this pressure differential isaccomplished by balancing a spring,assisted by manifold pressure, against adiaphragm which holds a ball valve on itsseat.

Pulsation Damper Although fuel pressure is maintained at aconstant value by the pressure regulator, thepulsing of the injectors causes minor fluctuations in rail pressure. The pulsationdamper acts as an accumulator to smoothout these pulsations, ensuring accurate fuelmetering.

The fuel pulsation damper is not used on allengines but can be used as a fuel pressurequick check on those engines which it isused. Noting the diaphragm, when pressureis present, the bolt head in the center of thediaphragm extends out flush with the top of the damper case.





Fuel Pressure Up SystemThe fuel pressure up system (FPU) isdesigned to reduce the possibility of vapor formation in the fuel rail after hot soak and isused on many TCCS engines. It utilizes anECU controlled Vacuum Switching Valve(VSV) to open an atmospheric bleed into themanifold reference line to the fuel pressureregulator.

This solenoid is energized during hot enginecranking and for up to two minutes after theengine starts. The ECU grounds the FPU

VSV based on input received from STA andTHW signals. Energizing the solenoid bleedsatmospheric pressure into the fuel pressureregulator vacuum chamber increasing fuelrail pressure to its maximum level.

On some engines, the ECU also monitorsengine load and rpm signals (Vs, PIM andNe) and energizes the VSV under heavy loadand high rpm operation to ensure maximumfuel rail pressure.





Fuel Pressure and Volume TestingSafety Tips: Prior to installing a fuel pressure gauge andchecking fuel pressure, residual pressure must be safelyrelieved to reduce the hazard of fire when the fuel line isopened. It is advisable to have a fire extinguisher whenever opening the fuel system.

Common gauge hookup locations are at thefuel rail, fuel filter, or the cold start valve usingSST #09268-45012 and #09268-45013-01.Repair manual procedures should alwaysbe followed. Whenever a fuel hoseconnection secured with a copper sealinggasket is opened, a new gasket should beused when the hose is re-secured after service.

Fuel pressure and volume tests can be

divided into six separate areas.

The following tests and specifications aregeneral guidelines; consult the repair manual for actual specifications andprocedures.

CAUTION: Perform this test only long enough todetermine if pressure rises above minimum specification;risk exists of blowing coupler hose off of pump. This test isonly necessary if other pressure tests indicate lower than

normal fuel pressure.

Fuel InjectorsThe fuel injector is an electro-mechanicaldevice which meters, atomizes and directsfuel into the intake manifold based onsignals from the ECU driver circuit(s). AllToyota engines used in the U.S.A. positionthe injectors, one per cylinder, directly behindthe intake valve. The injectors are installedwith an insulator/seal on the manifold end toisolate the injector from heat and to preventan atmospheric pressure leak into themanifold. The fuel delivery pipe serves tosecure the injector in place. Fuel is sealed onthe delivery pipe end by an O-ring andgrommet.

To reduce the possibility of vapor lock, which

tends to occur during high temperatureoperation, the 3S-GTE and 2TZ-FE enginesuse a side feed injector. This type of injector seals with an upper and lower O-ring. O-rings and insulators should always bereplaced when injectors are removed; theyshould never be re-used.





Air Assist SystemTo promote better fuel atomization, the 3VZ-FE engine uses an air assist system whichmeters air from the Idle Speed Control (ISC)valve directly to the nozzle of the fuel injector.

An adaptor for the air assist system is addedto a standard two-hole type injector to providean air distribution gallery. Air is mixed withfuel in the chamber formed by the injector insulator grommet and the lower O-ring.





Types Of Injectors In UseToyota currently uses four different types of fuel injectors depending on engineapplication. These can be broken down intopintle type and hole type (cone valve and ballvalve), high resistance and low resistance.

Pintle Type Injector - This was the originaldesign used on early Conventional and EFI/TCCS engines. This injector gets its namefrom the type of valve used to control fuelatomization and flow. It offers goodatomization of fuel but is susceptible todeposit buildup on the pintle valve. Depositscause restriction to fuel flow promoting leanfuel delivery and altered injector spraypattern.

Hole Type Injector - Hole type injectors wereintroduced on later model EFI/TCCS enginesto reduce concerns with injector deposits.The inject.on valve is recessed from the tip of the injector and fuel is delivered throughholes drilled in a director plate at the injector tip. The hole type injector offers good fuel

atomization while demonstrating better resistance to deposit buildup compared tothe pintle design. There are currently threedesigns of hole type injectors in use,including a side feed injector used on the 3S-GTE and 2TZ-FE engines.

High And Low Resistance Injector WindingsThere are two different types of injector coilwindings used depending on the type of drivecircuit used and whether or not an externalresistor is being used.

Low resistance injectors, which typicallyrange between 2 - 3 Ω@ 70'F, are used withan external resistor in a voltage controlleddriver circuit. Low resistance injectors arealso used without an external resistor in acurrent controlled driver circuit.

High resistance injectors, which typically runabout 13.8 Ω@ 70'F, do not require the useof an external resistor in a voltage controlleddriver circuit.





Injector Driver CircuitsCurrent is supplied to the ECU driver circuits(#10 and #20 in example) through the fuelinjectors. Current flows either directly fromthe ignition switch or from the EFI MainRelay. When the ECU driver circuit turns on,current flows to ground through the injector solenoid coil. The magnetic field createdcauses the injector to open against springtension. When the ECU driver circuit turns off,the spring closes the injector valve.

There are two common types of driver circuitscurrently in use on Toyota EFI engines; bothof these driver circuits work on the voltagecontrol principle. One uses an externalsolenoid resistor and a low resistanceinjector, the other using a high resistanceinjector without the solenoid resistor. In bothcases, the high circuit resistance is requiredto limit current flow through the injector winding. Without this control of the currentflow through the injector, the solenoid coilwould overheat, causing injector failure.





A third type of driver circuit was used byToyota on overseas models using the 4A-GEengine with D type EFI. Referred to as acurrent controlled driver circuit, it has never been used by Toyota on vehicles sold in the

U.S.A. but is widely used by other automanufacturers. This type of driver circuituses a low resistance injector and limitscurrent flow by controlling the gain of thedriver transistor. The advantage to the currentcontrolled driver circuit is the short timeperiod from when the driver transistor goeson to when the injector actually opens. Thisis a function of the speed with which currentflow reaches its peak.

In terms of injection opening time, theexternal resistor voltage controlled circuit issomewhat faster than the voltage controlledhigh resistance injector circuit. The trend,however, seems to be moving toward use of

this latter type of circuit due to its lower costand reliability. The ECU can compensate for slower opening time by increasing injector pulse width accordingly.

Caution: Never apply battery voltage directlyacross a low resistance injector. This willcause injector damage from solenoid coiloverheating. Use the proper SST inspectionwire will ensure proper series resistance.





Fuel Injection Patternand Injection Timing

Fuel injectors can be pulsed in one of four

patterns depending on application. Theseinjection patterns are:

• Simultaneous

• Two groups of two injectors each(four cylinder engines)

• Three groups of two injectors each(six cylinder engines)

• Independent (sequential)

The following chart represents fuel injectiongrouping and timing patterns.

Because injection timing is based on engine

rpm, the ECU must receive an rpm signal tooperate the injector driver circuits. WithConventional EFI, this signal comes directlyfrom the coil and is identified as IG. WithTCCS, the rpm and crankshaft positionidentification signals come from the Ne andG1 sensors located in the distributor. If thesesignals are lost, the ECU will not pulse theinjectors.





Fuel Injection VolumeFuel injection volume determination is basedupon the value of input sensor signals. Inaddition to volume control, the ECU canpulse the injectors either synchronously or non-synchronously with ignition events. Bothof these topics will be addressed in Chapter 5, "The Electronic Control System."

Common ServiceConcerns and Solutions

Injector Maintenance and Cleaning Although it is not the problem it was back inthe early to mid '80s, fuel injector restriction

is still an issue which needs to beaddressed from both a preventativemaintenance and repair viewpoint.

The best method of injector maintenance iscontinuous use of high quality fuels with alevel of detergency adequate to keep theinjector nozzles clean. It is also prudent tooffer injector cleaning service using theToyota approved injector cleaning systemand solvents. This service can be offered

whenever the vehicle is in for major serviceto maintain good engine performance andreduce the possibility of expensive injector replacement due to nozzle build-up.

It has been established that engines usinghole type injectors tend to have fewer problems with fouling than those with pintletype injectors. It has also been establishedthat use of low quality fuels which lackadequate detergent additives can lead to

injectors which become flow restrictive or which develop poor spray patterns.

When an injector becomes flow restricted,the volume of fuel delivered for a giveninjection duration will be reduced. Thiscondition will cause lean driveabilityproblems like stumble, hesitation, backfireand surging, especially during open loopoperation.

When an injector develops a poor spraypattern, fuel is not atomized and vaporizedproperly. It is entirely possible that the correctvolume of fuel will be delivered to the intakemanifold, however, this fuel will enter thecylinder as liquid droplets and will not burn.This condition will cause increasedhydrocarbon emissions and lean driveabilityproblems just as if the fuel delivery werelean. The symptoms of poor spray patterncan be very similar to those of flow restrictedinjectors.

When it comes time to diagnose these twoproblems, the recommended procedure is toremove the injectors from the engine andbench flow test each injector using the

following tools. This procedure is covered indetail in the appropriate repair manuals.

The following information covers the generaltest procedure.





Caution: Do not create sparks near fuelInjector and graduated cylinder. Keep fireextinguisher nearby while performing thistest.





Fuel Starvation Under LoadWhen troubleshooting performanceproblems which are related to insufficientfuel delivery, the fuel pickup filter should notbe overlooked as one possible source of restriction. Contaminants in fuels can restrictthis in tank filter sufficiently to cause engineperformance problems. In many cases, theengine will perform normally under light loadconditions.

The in-line filter, although considered to be a"lifetime" filter, can also cause fuel starvationunder load and hard starting if it becomesrestricted.

The best method of diagnosing suspectedfuel starvation which takes place under loadconditions is road testing with a fuelpressure monitor safely installed on thevehicle.

Injector Installation CautionsIt is very important to use new O-rings andgrommets when installing injectors toprevent leakage of fuel and potential air

leaks into the manifold. O-rings should be

lubricated with gasoline during installationand injectors should be checked for smoothrotation once installed to ensure proper seating.

Finally, many applications use a bi-directional spray pattern which requiresprecise positioning of the injector in relationto the cylinder head. Use care to followproper procedures outlined in the appropriaterepair manual.





Injector PlacementPlacement of injectors by cylinder is notusually necessary; however, starting with the1991 Tercel 3E-E engine, injectors with twodifferent hole placements are used. Theinjectors from cylinders number 1 and 3 arenot interchangeable with those installed incylinders number 2 and 4.

Always refer to the appropriate repair manualbefore installing the injectors on the 3E-E or any other engine as this will ensure correctinstallation. Failure to properly install andposition injectors can cause subtledriveability problems which may be difficult tofind after the fact.





Cold Start Injection SystemTo improve engine starting when coolanttemperatures are low, a supplementaryinjector is installed on many EFI engines.The cold start injection system consists of the following components:

1) Cold Start Injector

2) Start Injector Time Switch

3) ECU (most EFI/TCCS)

Cold Start Injector

The cold start injector is located at somecentral location in the intake manifold. It isdesigned to supplement the cranking air/fuelratio and prime the intake manifold in muchthe same way as a choke valve does whilecranking a carbureted engine.

This injector, controlled by the start injector time switch and ECU, sprays a finelyatomized mist of fuel while the engine iscranked to improve the speed with which theengine starts. To prevent engine flooding, the

injection time is limited by calibration of thestart injector time switch and a timer in theECU.

Start Injector Time SwitchThe function of the start injector time switch isto control the cold start injector ground circuitand to determine maximum injection durationwhile cranking. Its bi-metallic switch isheated by both engine coolant and anelectrical heater.

When the engine is cranked, current flowsfrom the STA circuit of the ignition switch tothe cold start injector. Current also flows to

the heater coils of the start injector timeswitch. When the bi-metallic contact of thestart injector time switch is closed, currentflows through the STJ circuit to ground,causing the cold start injector to deliver fuel.





As the bi-metallic switch is heated by electriccurrent, it opens, causing the STJ circuit tobe broken. This prevents the cold startinjector from delivering fuel.

Heater coils 1 and 2 are wired toaccommodate heater current flow whether or not the time switch is closed.

When the time switch contact is open,current can still flow through Heat Coil 2,thereby preventing the contact from closing inthe middle of a cranking cycle.

ECU Cold Start Injector ControlOn most TCCS engines, an alternate groundmay be supplied to the cold start injector bythe ECU at the STJ terminal. Based onsignals from the coolant temperaturesensor, the ECU can operate the cold start

The start injector time switch comes inseveral calibration values. These valuesdetermine the maximum temperature andmaximum time that the switch will remainclosed while the engine is being cranked.

Specifications for switch calibration arestamped on the switch. Applicationinformation is available through parts andtechnical service bulletins.

injector for up to three seconds regardless of the status of the time switch. Maximumcoolant temperature for ECU control is 113’F(45’C), above which the cold start injector willnot operate from any source.





Alternative Method of Cold Cranking EnrichmentSome engines have eliminated use of a coldstart injector entirely. Starting with the '91

model year, cold start injectors have beeneliminated on the 3E-E and 4A-FE engine.During cranking, the ECU looks at THW andlengthens injector pulse width sufficiently tostart the engine.

SummaryIn this chapter you have learned that the fueldelivery system pumps fuel from the tank tothe engine where it is delivered by anelectronically controlled fuel injector.

The fuel pump delivers fuel with enoughpressure and volume so the fuel pressureregulator can hold a constant pressuredifferential between intake manifold and fuelrail. Fuel which is delivered to the fuel rail butnot injected into the cylinders is returned tothe tank through a return pipe.

The fuel pump is energized by the circuitopening relay electrical circuit whenever theignition switch is on and the engine isrunning or cranking. Depending on fueldemand, some pumps are operated at twospeeds by routing current flow through or around a special current limiting resistor. Thefuel pump electrical circuit has a diagnosticmonitor built into the underhood checkconnector for diagnosis and testing.

Fuel injectors are electrically controlled by the

ECU and are driven individually, in groups, or simultaneously, depending on engineapplication. Current flow through the injector coil is controlled by using a high resistancecoil or a separate injector solenoid resistor.

To improve cold starting, some engines areequipped with a cold start injector systemwhich is controlled by a start time switchand/or the ECU.






The EFI/TCCS Ignition System

Overview of Toyota EFI/TCCSIgnition ControlThe ignition systems used on today'sEFI/TCCS equipped engines are not thatmuch different from the ignition system usedon the original 4M-E EFI engine. Primarycircuit current flow is controlled by an igniter based on signals generated by a magnetic

pickup (pickup coil) located in the distributor.

The ignition system has a dual purpose, todistribute a high voltage spark to the correctcylinder and to deliver it at the correct time.Ideal ignition timing will result in maximumcombustion pressure at about 10' ATDC.

The most significant difference betweenTCCS and Conventional EFI ignition systemsis the way spark advance angle is managed.The Conventional EFI system usesmechanical advance weights and vacuumdiaphragms to accomplish this. Starting with

the 5M-GE engine in 1983, the TCCS systemcontrols ignition spark timing electronicallyand adds an ignition confirmation signal as afail-safe measure.

There are two versions of electronic sparkmanagement used on TCCS equippedengines, the Electronic Spark Advance (ESA)and the Variable Advance Spark Timing(VAST) systems.

EFI #4 - TCCS IGNITION SYSTEM




Conventional EFI Ignition SystemSpark Advance Angle Control

In the Conventional EFI system, sparkadvance angle is determined by the positionof the distributor (initial timing), position of the magnetic pickup r eluctor teeth(centrifugal advance), and position of thebreaker plate and pickup coil winding(vacuum advance). The spark advance curveis determined by the calibration of the

centrifugal and vacuum advance springs.

Besides being subject to mechanical wear and mis-calibration, this type of sparkadvance calibration is very limited andinflexible when variations in coolanttemperature and engine

detonation characteristics are considered.Mechanical control of a spark curve is, atbest, a compromise. In some cases thetiming is optimal; in most cases it is not.

Engine RPM Signal

To indicate engine rpm to the EFI computer,

the Conventional EFI system uses the signalgenerated at the coil negative terminal (IG-).Because this system does not use ECUcontrolled timing, the rpm signal to the ECUhas no impact on spark timing whatsoever.The IG signal is used as an input for fuelinjection only.





Conventional EFI IgnitionSystem OperationWhen the engine is cranked, an alternating current signal is generated by the pickupcoil. This signal is shaped in the igniter andthen relayed through a control circuit to thebase of the primary circuit power transistor .

When the voltage at the base of thistransistor goes high, current begins to flowthrough the coil primary windings. When this

signal goes low, coil primary current stopsflowing, and a high voltage is induced intothe secondary winding. At cranking speed,spark plugs fire at initial timing, a function of distributor position in the engine.

When the engine is running, spark timing isdetermined by the relative positions of the

pickup reluctor (signal rotor) and the pickupcoil winding to each other. This relativeposition is controlled by the centrifugaladvance weights and vacuum advancediaphragm positions.

As engine speed increases, the reluctor advances in the same direction as distributor shaft rotation. This is a result of the

centrifugal advance operation.

As manifold vacuum applied to the vacuumcontroller is increased, the pickup coilwinding is moved opposite to distributor shaftrotation.

Both of these conditions cause the signalfrom the pick-up coil to occur sooner,advancing timing.





TCCS Ignition SparkManagement, Electronic SparkAdvance (ESA), and VariableAdvance Spark Timing (VAST)

The advent of ECU spark management

systems provides more precise control of ignition spark timing. The centrifugal andvacuum advances are eliminated; in their place are the engine sensors which monitor engine load (Vs or PIM) and speed (Ne).

Additionally, coolant temperature, detonation,and throttle position are monitored to providebetter spark accuracy as these conditionschange.

To provide for optimum spark advance under a wide variety of engine operating conditions,a spark advance map is developed andstored in a look up table in the ECU. Thismap provides for accurate spark timingduring any combination of engine speed,load, coolant temperature, and throttleposition while using feedback from a knocksensor to adjust for variations in fuel octane.

TCCS engines use two versions of ECUcontrolled spark management, ElectronicSpark Advance (ESA) and Variable SparkTiming (VAST).





To monitor engine rpm, the TCCS systemuses the signal from a magnetic pickupcalled the Ne pickup. The Ne pickup is verysimilar to the magnetic pickup coil used withConventional EFI. It has either four or 24reluctor teeth, depending on engineapplication.

Engines equipped with the ESA system (andthe 4A-GE engine with VAST) use a secondpickup in the distributor called the G sensor.The G sensor supplies the ECU withcrankshaft position information which isused as a reference for ignition and fuelinjector timing. Some engines use two Gsensors, identified as G1 and G2.

ESA Ignition System OperationIn the example above, when the engine iscranked, an alternating current signal isgenerated by a 24-tooth Ne pickup and afour-tooth G pickup. These signals are sentto the ECU where they are conditioned andrelayed to the microprocessor.

The microprocessor drives a trigger circuit,referred to as IGt (TR1). The IGt signal is sentto the igniter to switch the primary circuitpower transistor on and off.

While cranking, IGt fixes spark timing at apredetermined value. When the engine isrunning, timing is calculated based onsignals from engine speed, load,temperature, throttle position, and detonationsensors.

The IGt signal is advanced or retardeddepending on the final calculated timing. ESAcalculated timing is considered the idealignition time for a given set of engineconditions.

If the ECU fails to see an Ne or G signalwhile it is cranking, it will not produce an IGtsignal, thus preventing igniter operation.





VAST System OperationWhen the engine is cranked, an alternatingcurrent signal is generated by a four-toothmagnetic pickup in the distributor. Thisalternating current signal is sent directly tothe igniter where it is conditioned into asquare wave by a waveform shapingcircuit.

While cranking, this square wave signal issent to the ECU on the Ne wire and to the

igniter power transistor. The ignition systemdelivers spark at initial timing under thiscondition.

When the engine starts and exceeds apredetermined rpm, the ECU beginssending the lGt signal to the igniter. Theigniter switches to computed timing mode

and uses the IGt signal to operate the power transistor. Timing of IGt is based oninformation from various engine sensors.

Because the VAST system triggers the igniter directly from the magnetic pickup whilecranking, the engine will start even if the IGtcircuit to the igniter is open. If IGt signals arenot received by the igniter once the enginehas started, it will continue to run, defaulted

at initial timing, using signals from themagnetic pickup.

The VAST system is only used on the 2S-E,22R-E, 22R-TE, 4Y-E, and 4A-GE engines.





Igniter OperationWhen the IGt signal goes high, the primarycircuit power transistor TR2 turns on,allowing cur-rent to flow in the coil primarywinding. When the IGt signal goes low, theigniter interrupts primary circuit current flow,causing voltage induction into the coilsecondary winding.

With the ESA system, the time at which thepower transistor in the igniter turns on isfurther influenced by a dwell control circuit inside the igniter. As engine rpm increases,coil dwell time is increased by turning thetransistor on sooner. Therefore, the time atwhich the transistor is turned on determinesdwell while the time the transistor is turnedoff determines timing. Timing is controlled bythe ECU; dwell is controlled by the igniter.

Controlling dwell within the igniter allows thesame control over coil saturation time as theballast resistance does with theConventional EFI ignition system. It allowsmaximum coil saturation at high enginespeeds while limiting coil and igniter current,reducing heat, at lower speeds.

Spark Confirmation IGf Once a spark event takes place, an ignitionconfirmation signal called IGf is generated bythe igniter and sent to the ECU. The IGf signal tells the ECU that a spark event hasactually occurred. In the event of an ignitionfault, after approximately eight to eleven IGtsignals are sent to the igniter withoutreceiving an IGf confirmation, the ECU willenter a fail-safe mode, shutting down theinjectors to prevent potential catalystoverheating.





ECU Detection Of Crankshaft Angle

ESA System

In order to correctly time spark and injectionevents, the ECU monitors the relationshipbetween the Ne and G signals. With mostengines, the ECU determines the crankshaft

VAST System

Because all engines which use this systemhave a simultaneous injection pattern(except the 4A-GE), a G signal is notnecessary. The four-toothed pickup isdesigned to produce a pulse once every 180'of crankshaft rotation, signal timing

determined by the position of the distributor in the engine. Distributor positiondetermines Ne signal timing and, therefore,initial timing reference. The 4A-GE enginewith VAST, because it uses groupedinjection, utilizes a G sensor signalindicating camshaft position so the ECU canproperly time each injector group.

has reached 10' BTDC of the compressionstroke when it receives the first Ne signalfollowing a G1 (or G2). Initial timingadjustment is critical as all ECU timingcalculations assume this initial 10' BTDC asa reference point for the entire spark advancecurve.

Ignition Timing Strategy

The ECU determines ignition timing bycomparing engine operating parameters withspark advance values stored in its memory.The general formula for ignition timingfollows:

Initial timing + Basic advance angle +Corrective advance angle = Total sparkadvance.

Basic advance angle is computed usingsignals from crankshaft angle (G1),crankshaft speed (Ne), and engine load (Vsor PIM) sensors. Corrective timing factorsinclude adjustments for coolant temperature(THW) and presence of detonation (KNK).





Distributor-Less IgnitionSystem (DLI)

Used only on the 7M-GTE engine, DLI, as the

name implies, is an electronic sparkdistribution system which suppliessecondary current directly from the ignitioncoils to the spark plugs without the use of aconventional distributor. The DLI systemcontains the following major components:

1) Cam Position Sensor 2) Igniter 3) Ignition Coils (3)

Cam Position Sensor Very similar to the 7M-GE distributor without

the secondary distribution system, the camposition sensor houses the Ne, G1, and G2pickups. The Ne pickup reluctor has 24 teeth,its signal representing crankshaft speed.The G1 and G2 pickups produce signalsnear TDC compression stroke for cylinders#6 and #1, respectively. These signalsrepresent standard crankshaft angle andcylinder identification.

Igniter The igniter is similar to those used ondistributor type ignition systems butincorporates three separate primary circuits.The igniter determines timing of threeprimary circuits by the combination of IGdA

and IGdB input signals from the ECU. The IGtsignal is relayed by the igniter to the proper power transistor circuit to trigger the ignitionevent at the proper coil. The igniter alsosends the standard IGf confirmation signal tothe ECU for each ignition event which takesplace.





Ignition CoilsEach coil is connected in series betweenspark plugs of companion cylinders. For every engine cycle (720' of crankshaftrotation), ignition is carried out twice at eachcoil, both spark plugs firing simultaneously.One plug fires before TDC on thecompression stroke while the companionfires at the same position before TDC on theexhaust stroke. This type of secondarydistribution is referred to as waste spark.

The three ignition coils are mounted on thetop of the engine to the upper section of thehead cover. As you face the engine, the coilfor the 1-6 cylinder pair is on your left. The coilin the center serves the 3-4 cylinder pair, andthe coil to the right serves cylinder pair 2-5.





DLI System OperationWhen the engine is cranked, alternatingcurrent signals are generated by the 24-toothNe sensor and the two G sensors (G1 andG2). The G sensors are 360' out of phase.

The G sensors represent #1 and #6 pistonsapproaching TDC on the compressionstroke. These signals are received by theECU where they are conditioned andprocessed by the ESA microprocessor.

The ESA microprocessor serves twofunctions. It generates an IGt signal andgenerates cylinder identification signals,IGdA and IGdB, which allow the DLI igniter totrigger the correct coil while cranking theengine.

These signals are sent to the DLI igniter which electronically determines proper primary signal distribution based on thecombination of IGdA and IGdB signals. Theigniter distributes the IGt signal to the proper coil driver circuit and determines dwell periodbased on coil primary current flow. The ESAcalculations for spark advance angle workthe same as with distributor type ignitionsystems.

The table below shows how the igniter isable to calculate crankshaft position andproperly distribute the IGt signal to thetransistor driver circuit connected to therelevant ignition coil.





Ignition System ServiceTroubleshooting the Ignition System

No Spark Output

The following procedures assume that aspark tester reveals no spark at two differentcylinders while the engine is cranked. Theseprocedures and specifications are generalguidelines. Consult the appropriate repair manual for more specific information aboutthe vehicle you are troubleshooting.

Preliminary checks

1) Ensure battery condition prior to ignitionsystem analysis.2) Check and confirm good connections at

distributor, igniter, and coil.3) Basic secondary leakage checks at coil

and coil wire.

Primary circuit checks

1) Confirm power supply to igniter and coilpositive (+) terminal. Confirm connections

at coil positive and negative (-) terminals.

2) Using a test light or logic probe, check for primary switching at the coil (-) terminalwhile cranking engine. Blinking lightconfirms primary switching is takingplace; check coil wire, coil secondarywinding resistance, or secondary leakagein distributor cap.

3) The power transistor(s) in the igniter gettheir ground through the igniter case tothe vehicle chassis; always confirm goodground continuity prior to trouble shooting.

4) Confirm coil primary and secondarywindings resistance. Confirm primarywindings are not grounded.

5) Confirm signal status from Ne and Gpickups to ECU (ESA system) or to igniter (VAST system) using an oscilloscope or logic probe.

• If a fault is detected, check pickup(s) for proper resistance and shorts to ground.Check electrical connections.

• If signal amplitude is low, check signalgenerator gap(s).

6) Confirm signal status from ECU IGt circuitto igniter using an oscilloscope or logicprobe.

7) On 7M-GTE, check power transistor inigniter. Bias transistor base using aremote 3 volt battery as power source.Use ohmmeter to check for continuity fromprimary circuit to ground (see procedurein repair manual for details).





8) Check pickup gaps and coil resistancesagainst specifications. If gap and/or resistance is not within specification,replace faulty component.





Timing Will Not AdvanceProperly (VAST System)

The following checks assume that theengine runs but timing will not advance.

The design of the VAST system will allow theignition system to function at initial timing inthe event that the IGt signal does not reachthe igniter. If this condition occurs, theignition system will be locked at initial timingregardless of engine speed or load. TheECU has no way to monitor for this fault, sothere will be no indication of this condition

other than a loss of engine performance.

To check for this condition:

1) Monitor the IGt wire at the igniter using anoscilloscope or logic probe.

2) If a good signal is being sent out on IGt,check the connection at the igniter.

3) Once connections are confirmed, the

igniter is the last item left which cancause the problem.

Timing Seems Out of RangeFor Conditions (VAST or ESA)

In some cases, driveability symptoms or acheck of timing reveal advance which is out of range for input conditions. This situationcould be caused by incorrect sensor information reaching the ECU.

An example of this type of problem can beillustrated by a manifold pressure sensor which is out of range low. Lower than normalvoltage from the sensor would indicate a lightload condition to the ECU. The ECU

responds to light load operation by advancingthe timing. If the vehicle is being operatedunder moderate to heavy load with too muchspark advance, detonation will likely result.

When this type of condition is suspected, it isrecommended to perform a standard voltagecheck of all major sensor inputs to the ECU.If any sensor is found out of normal range, itis a likely cause of the problem. The subjectof sensor signal values is addressed in,

"Electronic Engine Controls."





Adjustment Of InitialIgnition Timing

All engines equipped with TCCS utilize a testterminal (T or TE1) somewhere under the

hood. Early TCCS utilizes a two-terminalcheck connector in the wiring harness. Thisyellow body connector contains circuits T andE1, which when jumpered, default the TCCSsystem to initial timing. The location of thistest terminal varies between applications.Refer to the appropriate repair manual for connector location.

A new design multipurpose check connector began phase-in starting with 1985 models.

By 1986 model year, all vehicles areequipped with this new style connector.Connectors are typically located in the fender area on either side, or near the bulkhead, inplain view. With the advent of test terminalsfor the ECT, TEMS, SRS, and etc., the TCCStest terminal has been renamed TE1 todistinguish it from the others.

To check timing on any TCCS equipped

engine:

1) Engine at normal operating temperature.

2) Jumper T (TE1) to El using SST 09843-18020 (or equivalent).

3) Wait for engine rpm to stabilize (speed may riseto I K to 1.3 K rpm for 5 seconds).

4) Use timing light to confirm initial timing as per repair manual procedure.

• Make sure rpm is within specified range.• Adjust timing as necessary by rotating thedistributor (cam position sensor on 7M-GTE).

5) Remove SST jumper.

6) Recheck timing; it should be advanced (at least3' to 18') from initial with SST removed.





SummaryIn this chapter you have learned how theECU electronically controls ignition timing,delivering spark at the optimum momentbased on engine speed, load, temperatureand quality of fuel. The spark advance curveis stored in a look up table in the ECUmemory.

There are two types of ECU controlled sparkadvance systems used on Toyota TCCSequipped engines, the Variable AdvanceSpark Timing system (VAST) and theElectronic Spark Advance system (ESA). Themain difference between these systems isthe magnetic pickup in the distributor (Nepickup) reports to the igniter on the VASTsystem and directly to the ECU on the ESAsystem.

An ignition confirmation signal is generatedby the igniter which signals the ECU witheach ignition event. The IGf signal is used toprovide the ECU with a fail-safe fuel cutoff if ignition spark is lost.

The Distributorless Ignition system (DLI)provides secondary distribution by means of a three-coil waste spark system. Twocompanion spark plugs are connected toeach end of the ignition coil secondarywindings. These plugs fire simultaneouslyeach time the cylinder pair approaches TDC,one spark igniting the mixture, the other wasted on the exhaust stroke.






Overview

The EFl/TCCS system is an electroniccontrol system which provides Toyotaengines with the means to properly meter the fuel and control spark advance angle.The system can be divided into three distinctelements with three operational phases.

The three system elements are:

• Input Sensors

• Electronic Control Unit (A Microcomputer)

• Output Actuators

ENGINE CONTROLS - INPUT SENSORS




The electronic control system is responsiblefor monitoring and managing enginefunctions which were previously performedby mechanical devices like carburetors,vacuum, and centrifugal advance units. In an

electronic control system, these functionsare managed in three phases.

• The input phase of electronic control allowthe Electronic Control Unit (ECU) to monitor engine operating conditions, utilizinginformation from the input sensors.

• The process phase of electronic controlrequires the ECU to use this inputinformation to make operating decisionsabout the fuel and spark advance systems.

• The output phase of electronic controlrequires the ECU to control the outputactuators, the fuel injectors, and igniter toachieve the desired fuel metering andspark timing.

In this chapter, we will explore the details of the electronic control system hardware andsoftware. The chapter starts with a thoroughexamination of the system's input sensor circuits and the ECU power distributionsystem. It concludes with a closer look at theECU process functions and the controlstrategy use( for optimum fuel metering andspark advance angle control.

The Microcomputer

The heart of the TCCS system is amicrocomputer. A microcomputer is a

device which receives information,processes it, and makes decisions basedon a set of program instructions. Themicrocomputer exercises control over theoutput actuators to carry out theseinstructions.

The use of microcomputers has taken thescience of engine management into thespace age by increasing the speed with

which information can be processed andallowing the electronic control system tomanage more engine functions. With theability to process information so rapidly, themodern ECU is capable of carrying out its

programmed instructions with extremeaccuracy. Engine management can addressvirtually every condition the engine willencounter so that for any engine condition,the ECU will deliver optimum fuel and spark.

Evolution of Toyota's Electronic FuelInjection Systems

Early Conventional EFI computers were firstconfigured from analog circuits, and theycontrolled only fuel delivery and injection. Themodem Electronic Control Units (ECU) utilizedigital circuits and microprocessors whichhave served to improve EFI systemcapabilities.

Modern TCCS engine controls, introduced tothe U.S.A. market in 1983, are capable of managing fuel delivery, idle speed control(ISC), electronic spark advance (ESA), andemissions systems with extraordinary speedand accuracy.

In the evolution of Toyota's fuel injection,three levels of electronic control refinementshave taken place.

• Conventional EFI

• P7/EFI

• EFI/TCCS

The main difference between these systemsis the capability of the ECU. Thesecapabilities have grown from simple fuelcontrol to the addition of self-diagnostics tothe control of ignition spark advance andmore. The following chart summarizes basiccapabilities by system and can be used as aguide in identification and troubleshooting.





System identification is relatively simple.

• The Conventional EFI system has no checkengine light.

• The P7/EFI system has a check enginelight but has a mechanical advancedistributor.

• The EFI/TCCS system has a check enginelight and an electronic advance distributor.

The Input Sensors,Information Source for the ECU

In an electronic control system, the ECUuses its sensors in much the same manner as we use our five senses. Our sense of

touch tells us when things are hot or cold; our sense of hearing allows us to distinguishone sound from another; our sense of smelltells us when fresh coffee is brewingsomewhere nearby. Sensors give the ECUsimilar abilities: the ability to feel thetemperature of the engine coolant, to listenfor the sound of detonation, and to smell theexhaust stream for the presence of sufficientoxygen.

This lesson on input sensors will addresshow each major ECU input sensor circuitworks. Each sensor circuit will be brokendown so you can see its individualcomponents: the sensor, electrical wiring,and the ECU.





Overview

The EFl/TCCS system is an electroniccontrol system which provides Toyotaengines with the means to properly meter the fuel and control spark advance angle.The system can be divided into three distinctelements with three operational phases.

The three system elements are:

• Input Sensors

• Electronic Control Unit (A Microcomputer)

• Output Actuators





Input Sensors Used in BasicInjection and Spark Calculation

Engine Air Flow Sensing

Vane Type Air Flow Meters(Vs, General Information)

The vane type air flow meter is located in theair induction system inlet pipe between theair cleaner and the throttle body. It iscomposed of the measuring plate,compensation plate, return spring,potentiometer, and by-pass passage. Thesensor also incorporates the idle mixture

adjusting screw (factory sealed), the fuelpump switch, and the intake air temperaturesensor (which will be addressed later in thislesson). Because intake air volume is adirect measure of the load placed on anengine, the vane type air flow meter providesthe most important input to the ECU for fueland spark calculations.

When air passes through the air flow meter,it forces the measuring plate open to a point

where it balances with the force of the returnspring. The damping chamber andcompensation plate prevent vibration of themeasuring plate during periods of suddenintake air volume changes.

The potentiometer, which is connected to themeasuring plate and rotates on the sameaxis, converts the mechanical movement of the measuring plate into a variable voltagesignal. Movement of the measuring plate and

the analog voltage signal produced by thissensor are proportional to the volume of air entering the intake manifold.

Vane Air How Meter Electrical Circuit

The sensor movable contact is attached tothe measuring plate and rides on a fixedresistor wired between the reference voltageinput and the ground. As the volume of air entering the engine increases, the movablecontact moves across the fixed resistor,causing a change in signal output voltage.

There are two designs of vane air flowmeters used on Toyota L type EFI systems.The first design generates a signal whichvaries from low voltage at low air volumes tohigh voltage at high air volumes. The seconddesign sensor has opposite signalcharacteristics. These sensors also operateon different reference voltages. Both sensor designs integrate an intake air temperaturesensor into the air flow meter.





First Design Vane Air How Meter

The first design air flow meter is found on allConventional EFI engines and many later model TCCS equipped engines. This sensor

has an electrical connector with seventerminals, four of which are used for air flowmeasurement.

Air Flow Sensor Terminal Identification(First Design Sensor)

The air flow meter and ECU are wired asshown in the diagram. Signal characteristicsare depicted by the accompanying graph. The

use of battery voltage, VB, as a sensor inputnecessitates the use of the Vc terminal as aconstant reference signal for the ECU. This isbecause battery voltage may change withvariances in electrical load and ambienttemperatures. Without the use of a constantreference voltage, these changes wouldcause a change in the Vs signal valuerecognized by the ECU.





Second Design Air How Meter

The second design air flow meter wasintroduced on the '85 5M-GE engine, and itsuse expanded with many late model TCCSequipped engines. This sensor has an

electrical connector with seven terminals,three of which are used for air flowmeasurement.

Air Flow Sensor Terminal Identification

(Second Design Sensor)

The air flow meter and ECU are wired asshown in the diagram; signal characteristicsare depicted by the accompanying graph. Theuse of a regulated 5 volt reference eliminates

the need for the VB terminal with this sensor circuit.

Resistors R1 and R2 provide self diagnosticcapabilities and allow for a fail-safe voltage atthe ECU in the event of an open circuit. Thesetwo resistors have a very high resistancevalue (relative to r1 and r2) and essentiallyhave no electrical effect on the circuit under normal operating conditions. They will,however, affect the open circuit voltagemeasured on the Vs wire at the ECU.





Karman Vortex Air Flow Meter (Ks)

The Karman vortex air flow meter is currentlyused on the 7M-GTE Toyota engine and the2JZ-GE and 1UZ-FE Lexus engines. It is

located in the air induction system inlet pipebetween the air cleaner and the throttle body.The sensor is composed of a photocoupler and mirror, a vortex generator, and anintegrated circuit (IC) which together,measure the frequency of the vorticesgenerated by air entering the intake system.

When compared with the vane type air flowmeter, the Karman vortex meter is smaller,lighter, and offers less restriction to incomingair. Similar to the vane type air meter, the

Karman vortex meter integrates the intake air temperature sensor into the meter assembly.

The sensor has an electrical connector withfive terminals, three of which are used for air flow measurement.

Karman Vortex Air Flow Meter

Terminal Identification





The Karman vortex air flow meter and ECUare wired as shown in the diagram. Signalcharacteristics are represented by theillustration of the variable frequency square

wave. Because of the pull-up resistor wiredbetween the Vcc and Ks circuit, the Ks signalwill go to 5 volts if the circuit is opened.

When air passes through the air flow meter,the vortex generator creates a swirling of theair downstream. This swirling effect isreferred to as a "Karman vortex." The

frequency of this Karman vortex varies withthe velocity of the air entering the air flowmeter and other variables. The photocoupler and metal foil mirror are used to detectchanges in these vortices.





The metal foil mirror is used to reflect lightfrom the LED to the photo transistor. The foilis positioned directly above a pressuredirecting hole which causes it to oscillate

with the changes in vortex frequency. As themirror

oscillates, the 5 volt Vcc reference isswitched to ground by a photo transistor within the sensor. The resulting digital signalis a 5 volt square wave which increases in

frequency in proportion to increases in intakeair flow.





Manifold Absolute Pressure Sensor

The manifold absolute pressure sensor (sometimes referred to as vacuum sensor)is used on engines equipped with D type

EFI. It is typically located somewhere on thebulkhead with a vacuum line leading directlyto the intake manifold. It measures intake air volume by monitoring changes in manifoldabsolute pressure, a function of engine load.

The sensor consists of a piezoresistivesilicon chip and an Integrated Circuit (IC). Aperfect vacuum is applied to one side of the

silicon chip and manifold pressure applied tothe other side. When pressure in the intakemanifold changes, the silicon chip flexes,causing a change in its resistance. Thevarying resistance of the sensor causes achange in signal voltage at the PIM (PressureIntake Manifold) terminal.





The manifold absolute pressure sensor hasan electrical connector with three terminals.

Manifold Absolute Pressure Sensor Terminal Identification

The sensor and ECU are wired as shown inthe diagram. As manifold pressure increases(approaches atmospheric pressure) there isa proportionate increase in PIM signal

voltage. This analog signal characteristic isdepicted in the accompanying graph.

TO check sensor calibration, signal voltageshould be checked against the standardsshown on the graph, and a voltage dropcheck should be performed over the entireoperating range of the sensor.





Engine Speed andCrankshaft Angle Sensing

On TCCS equipped engines, the Ne and G1signals inform the ECU of engine rpm and

crankshaft angle. This information, alongwith information from the air flow or manifoldpressure sensor, allows the ECU tocalculate the engine's basic operating load.Based on measured load, basic injectionand spark advance angle can be accuratelycalculated.

Ne Signal (Number of Engine Revolutions)

The Ne signal generator consists of a pickupcoil and toothed timing rotor. The number of teeth on the signal timing rotor is determinedby the system used. The Ne sensor produces an alternating current waveform

signal and is of critical importance to theECU. If this signal fails to reach the ECU, the

engine will not run.

G or G1 Signal (Group #1)

The G signal generator is very similar to theNe signal generator. The G1 signalrepresents the standard crankshaft angleand is used by the ECU to determine ignitionand injection timing in relation to TDC.

Depending on engine, there are differentvariations of Ne and G1 signal generators.The following illustrations show therelationship between the Ne and G1 signalsand the different variations of signalgenerators.





lGf Signal

The IGf signal is generated by the igniter onEFI/TCCS systems. The ECU supplies a 5volt reference through a pull-up resistor tothe lGf signal generation circuit in the igniter.

When a spark plug fires, the IGf signalgeneration circuit pulls the five volts toground, causing a pulse to be sensed at theECU. One pulse is generated by the igniter for each ignition event which is carried out.

IG Signal

On Conventional EFI engines, the IG signalis used to inform the ECU of engine rpm.This signal is generated directly from the coilnegative terminal or from an electricallyequivalent point inside the igniter on the early

The IGf signal confirms that ignition hasactually occurred. In the event of a failure totrigger an ignition event, the ECU will shutdown injector pulses to protect the catalystfrom flooding with raw fuel. Typically this fail-

safe shutdown occurs within eight to elevenIGt signals after the IGf signal is lost. Thiscondition can occur with any primary ignitionsystem fault, an igniter failure, a problem withthe IGf circuit wiring, or with a faulty ECU.

P-7 2S-E engine. Conventional EFI enginesdo not use an Ne or G sensor and do not usean IGf signal. The IG signal is also used bythe ECU to trigger injection pulses; therefore,if this signal is lost, the engine will stall for lack of injection pulse.





Input Sensors Used For Injectionand Spark Corrections

Water Temperature Sensor (THW)The water temperature sensor is typicallylocated near the cylinder head water outlet. Itmonitors engine coolant temperature bymeans of an internally mounted thermistor.The thermistor has a negative temperaturecoefficient (NTC), so its resistance valuedecreases as coolant temperature rises.The accompanying resistance graphdemonstrates this relationship.

The water temperature sensor is requiredbecause fuel vaporization is less efficientwhen the engine is cold. Internal enginefriction is also higher during cold operation,increasing operating load. The THW signal isused by the ECU to determine how much fuelenrichment correction is necessary to providegood cold engine performance. In addition tofuel calculations, the THW signal plays amajor role is almost every other function thatthe ECU serves.





The water temperature sensor has a twoterminal electrical connector attached toeither end of the thermistor element.

Water Temperature Sensor Terminal Identification

The sensor and ECU are wired as shown inthe diagram. Signal voltage characteristicsare determined by the value of the pull-upresistor , located inside the ECU, either 2.7

KΩ or 5 M. The graphs accompanying thediagram give approximate voltagespecifications. To determine which pull-upresistor a particular ECU uses, refer to thetechnical reference charts in Appendix B of this book.





Air Temperature Sensor (THA)

The air temperature sensor monitors thetemperature of air entering the intakemanifold by means of a thermistor. This

thermistor is integrated within the air flowmeter on L type systems and located in theintake air hose just downstream of the air cleaner on D type systems. It has the sameresistance characteristics as the water temperature sensor.





This sensor has a two-terminal electricalconnector attached to either end of thethermistor element.

Air Temperature Sensor Terminal Identification

The air temperature sensor and ECU arewired as shown in the diagram. Resistanceand voltage signal characteristics arerepresented by the accompanying graphs.

An intake air temperature monitor isnecessary in the EFI system because thepressure and density of air changes withtemperature. Because air is more densewhen cold, the ECU factors intake air temperature into the fuel correction program.





Throttle Angle andClosed Throttle Sensing

Throttle position sensors typically mount on

the throttle body, directly to the end of thethrottle shaft. Depending on engine andmodel year, Toyota EFI equipped enginesuse one of two different types of throttleposition sensors. These sensors arecategorized as on-off type and linear type.The linear type sensor is typically used onmost late model Electronically ControlledTransmission (ECT) equipped vehicles.

The on-off type sensor circuits can be further

broken down into first and second design.This sensor is typically used on manual or non-ECT transmission equippedapplications.

All throttle sensors, regardless of design,supply the ECU with vital information aboutidle status and driver demand. Thisinformation is used by the ECU to make

judgments about power enrichment,deceleration fuel cut-off, idle stability, andspark advance angle corrections.





On-Off Type Throttle PositionSensors (IDL & PSW)

The on-off type throttle position sensor is a

simple switch device which, depending onapplication, either pulls a reference voltageto ground or sends a battery voltage signal tothe ECU. The on-off throttle position sensorsare electrically wired to the ECU as shown inthe accompanying diagrams.

First Design On-Off Type Sensor

The first design sensor is used onConventional EFI engines. It utilizes a dual

position contact which switches a batteryvoltage signal to either the IDL or PSW inputsat the ECU. This switching action causes thevoltage signal at the ECU to go highwhenever the switch contacts are closed.

Referring to the voltage graph, IDL signalvoltage is high when the throttle is closedand goes low when the throttle exceeds a 1.5'opening. PSW voltage is low until the throttleexceeds about a 70' opening; then it goeshigh.





Second Design On-Off Type Sensor

The second design sensor, which is usedon many late model TCCS equippedengines, utilizes a dual position contact toswitch an ECU reference voltage to ground.

This switching action causes the signal atthe ECU to go low whenever the switchcontacts are closed.

Referring to the voltage graph, IDL signalvoltage is low when the throttle is closed andgoes high when the throttle exceeds a 1.5'opening. PSW voltage is high until the throttleopens to about 70’; then it goes low.

The three wire electrical connector terminalsare identified as follows.

1 st and 2nd Design On-Off Throttle

Position Sensor Terminal Identification





On '83 and '84 Cressidas/Supras and '83through '86 Camrys equipped with anElectronically Controlled Transmission(ECT), a modified sensor, which

incorporates three additional signal wiresdesignated L1, L2, and L3, is used. Thesesignals represent throttle opening angles inbetween the 1.5' IDL and 70' PSW signals.The L1, L2, and L3 signals are used by theECT system and are generated in a similar manner as the IDL and PSW signals on the2nd design sensor. The TCCS ECU onlyuses the IDL and PSW signals from thissensor.

Linear Throttle Position Sensor (VTA)

The linear throttle position sensor ismounted to the throttle body. It is composedof two movable contacts, a fixed resistor, and

four electrical terminals. The two movablecontacts move along the same axis as thethrottle valve. One is used for the throttleopening angle signal (VTA) and the other for the closed throttle signal (IDL).





As the throttle opens, a potentiometer circuitconverts the mechanical movement of thethrottle valve into a variable voltage signal.The voltage produced by this sensor isproportional to the throttle valve opening

angle.

The Linear Throttle Position Sensor has anelectrical connector with four terminals.

Linear Throttle Position Sensor Terminal Identification

The sensor and ECU are wired as shown inthe diagram. As the throttle valve opens, thesensor VTA contact moves closer to thevoltage source, causing a signal voltageincrease.

At closed throttle, the IDL contact is heldclosed. This pulls the IDL signal circuit toground. As the throttle opens, the IDL contactbreaks, causing the digital IDL signal voltageto go from low to high. These signalcharacteristics are depicted in theaccompanying graph.

Resistors R1 and R2 provide self diagnosticcapabilities and allow for a fail-safe voltage atthe ECU in the event of an open circuit. Thesetwo resistors have a very high resistancevalue and essentially have no electrical effecton the circuit under normal operatingconditions. They will, however, affect the opencircuit voltage measured on the VTA wire atthe ECU.





Exhaust Oxygen Content Sensing (OX1)

Exhaust oxygen sensors are used on ToyotaEFI and EFI/TCCS equipped engines toprovide air/fuel ratio feedback information to

the ECU. This information is used toconstantly adjust the air/fuel ratio tostoichiometry during warm idle and cruiseoperating conditions. The stoichiometric air/fuel ratio delivers one pound of fuel for each 14.7 pounds of air entering the intakemanifold and results in the most efficientcombustion and catalyst operation. When theelectronic control system is usinginformation from the oxygen sensor to adjustair/fuel ratio, the system is said to beoperating in closed loop.

Exhaust oxygen sensor efficiency isdependent upon its operating temperature.The sensor will only generate an accuratesignal when it has reached its minimumoperating temperature of 750'F. Therefore,the oxygen sensor is typically located in theexhaust stream at the manifold collector.This location is close enough to the exhaustvalves to maintain adequate operatingtemperature under most driving conditionsand allows a representative exhaust samplefrom all cylinders.

Open and Closed Loop Operation

In addition to promoting efficient combustionand catalyst operation, a stoichiometricair/fuel ratio also promotes excellent fuel

economy. This relatively lean mixture isdesirable during cruise and idle operation;however, other operating conditions oftenrequire a richer air/fuel ratio. When theelectronic control system ignores signalsfrom the oxygen sensor and does not correctthe air/fuel ratio to 14.7:1, the system is saidto be operating in open loop.

In order to prevent overheating of the catalystand ensure good driveability, open loopoperation is required under the followingconditions:

• During engine starting

• During cold engine operation

• During moderate to heavy load operation

• During acceleration and deceleration

During open loop operation, the ECU ignoresinformation from the exhaust oxygen sensor and bases fuel injection duration calculationsexclusively on the other input sensors.





Exhaust Oxygen SensorsToyota engines utilize two different types of oxygen sensors. The zirconium dioxide sensor isused on all engines except the '90 and later 4A-GEFederal and 3VZ-E California 2WD truck engines.

These two engines use a titania oxide sensor.

To bring the system to closed loop operation morerapidly, many engines use a heated exhaustoxygen sensor. The heated sensor provides moreaccurate exhaust sampling during idle and lowspeed operation when exhaust temperatures arerelatively low. Use of a heated sensor allowsclosed loop operation earlier during engine warm-up cycles and also allows more flexibility inoxygen sensor location. These factors help inmeeting strict exhaust emissions controlstandards.

Engines produced for sale in California alsoincorporate a Sub-Oxygen Sensor which helpsimprove the efficiency of the catalyst system. Thissensor is located after the catalyst and is used tofine tune the air/fuel ratio delivered by theinjectors, helping to optimize catalyst efficiency.

Zirconium Dioxide Sensor The zirconium dioxideoxygen sensor is an electro-chemical devicewhich compares the oxygen content of theexhaust stream with the oxygen in an ambient air sample. It consists of a zirconium dioxide (Zr02)element sandwiched between two platinumelectrodes.

This sensor behaves very similar to a single cellbattery. The electrodes act as the positive (+) andnegative (-) plates, and the zirconium dioxideelement acts as the electrolyte.

Rich air/fuel ratio: If the oxygen concentration onthe inside plate differs greatly from that on theoutside plate, as it would with a rich air/fuel ratio,electrons will flow through the Zr02 element to theplate exposed to the high oxygen concentration.

During rich operating conditions, the inside, or positive plate, is exposed to a much higher concentration of oxygen than the outside, or negative plate. This creates a difference inelectrical potential, or voltage, which is measuredby a comparator circuit in the E CU.

Lean air/fuel ratio: When the air/fuel ratiobecomes lean, the oxygen content of the exhaustgas increases significantly. Because both platesare now exposed to a relatively high concentrationof oxygen, electrons balance equally between thetwo plates. This eliminates the electrical potential

between the plates.

Zirconium Dioxide Oxygen Sensor Operating Characteristics





Zr02 sensor voltage signal and ECUprocessing: The voltage signal produced by.the oxygen sensor is relatively small. Duringthe richest operating conditions, this signalapproaches 1000 millivolts (1 volt).

The Zr02 oxygen sensor is wired as shownin the diagram. Voltage characteristics aredepicted in the accompanying graph.

As the voltage graph illustrates, the output of the Zr02 sensor acts almost like a switch. Asthe air/fuel ratio passes through thestoichiometric range, voltage rapidlyswitches from high to low.

The ECU comparator circuit is designed tomonitor the voltage from the sensor andsend a digital signal to the microprocessor. If sensor voltage is above the comparator switch point, z 1/2 volt, the comparator output

will be high. If the sensor voltage is below thecomparator switch point, the comparator output will be low. The microcomputer monitors the output of the comparator todetermine how much oxygen remains in theexhaust stream after combustion occurs.





Titania Oxide Sensor This four-terminaldevice is a variable resistance sensor withheater. It is connected in series between theOX+ reference and a fixed resistance locatedinside the ECU. This circuit operates

similarly to a thermistor circuit.

The properties of the thick film titaniaelement are such that as oxygenconcentration of the exhaust gas changes,the resistance of the sensor changes. As thesensor resistance changes, the signalvoltage at the ECU also changes.

TITANIA OXIDE SENSORRESISTANCE CHARACTERISTICS

The titania sensor and ECU are wired asshown in the diagram. A one-volt potential issupplied at all times to the OX+ terminal of the sensor. The resistance value of thesensor changes abruptly as thestoichiometric boundary is crossed. Theaccompanying voltage and resistancegraphs depict these characteristics and their influence on OX signal voltage.

The ECU comparator circuit is designed tomonitor the voltage drop across R1. As thevoltage drop across the sensor increases,the drop across R1 decreases and viceversa. This gives the OX signal voltage thesame characteristic as the Zr02 sensor.

If sensor voltage drop is low, as it would bewith a rich mixture, OX signal voltage will beabove the comparator switch point, 450millivolts, and the comparator output will behigh. If the sensor voltage drop is high, OXsignal voltage will be below the comparator switch point and the comparator output willbe low.





Sub-Oxygen Sensor (OX2)

The sub-oxygen sensor is used on Californiaand some Federal engines. It is used tomonitor the exhaust stream after the catalyst

to determine if the air/fuel mixture is withinthe range for efficient converter operation.

The sub-oxygen sensor is identical to theZr02 main oxygen sensor located ahead of the catalyst. Information from this sensor is

used by the ECU to fine tune the air/fuel ratioand improve emissions.





Oxygen Sensor Heater Circuits (HT)

Oxygen sensors work very efficiently whenthe sensing element temperature is above750'F (400'C). At warm cruise, it is not difficult

to maintain oxygen sensor temperatures ator above this point. However, when theengine is first started or when idling or whendriving under very light load, the oxygensensor can cool down, forcing the fuelsystem to return to open loop operation.

The oxygen sensor heater control systemmaintains sensor accuracy by turning on theheater element whenever intake air volumeis low (exhaust temperatures are low under these conditions). By heating the sensor electrically, sensor detection performance isenhanced.

This allows feedback operation under conditions which might otherwise requireopen loop fuel control. The ECU monitors the

following parameters and cycles the oxygensensor heater on:

• When intake air flow is below a given point.

and

• coolant temperature is above approximately32'F (O'C).

• specified time has elapsed after starting.

The oxygen sensor heater and ECU arewired as shown in the diagram. Whenever the above mentioned conditions are met, theECU turns on the driver transistor to supply aground path for heater current.





Other Inputs Affecting Injectionand Spark Correction

Engine Cranking Signal (STA)STA is a digital signal which is used by theECU to determine if the engine is beingcranked. The signal is generated at the ST1terminal of the ignition switch and is used bythe ECU primarily to increase fuel injectionvolume during cranking.

The STA circuit is wired to the ECU as shownin the diagram. The ECU will sense crankingvoltage at the STA terminal whenever theignition is switched to the "start" position aslong as the neutral or clutch switch is closed.





Engine Detonation (Knock) Signal (KNK)

Knock Sensor The knock sensor is a piezoelectric devicemounted to the cylinder block which generates a

voltage whenever it is exposed to vibration. Whenengine detonation occurs, vibration of the cylinder block causes the sensor to generate a voltagesignal. The sensor signal varies in amplitude depending on the intensity of knock.

Typically, detonation vibration occurs in the 7KHzrange (7 thousand cycles per second). Knocksensor and ECU designs take advantage of thisfact.

There are two different types of knock sensorsused on Toyota engines. The mass type sensor

produces a voltage output over a wide inputfrequency range; however, its signal output isgreatest at a vibration frequency of approximately7KHz. With this type of sensor, the ECU uses afilter circuit to distinguish between backgroundnoise and actual engine knock.

The resonance type sensor is tuned into a verynarrow frequency band and only produces asignificant signal voltage when exposed tovibrations in the 7KHz range. The ECU requiresless complicated filter circuitry with this type of sensor.

ECU Detonation ControlThe ECU and knock sensor are wired as shown inthe diagram. When engine detonation occurs, the

ECU monitors knock sensor signal feedback todetermine the degree of detonation taking place.This is accomplished by filtering out sensor signalvoltage which does not go above preprogrammedamplitude parameters. Because other backgroundnoise and vibration cause some signal output fromthe knock sensor, the ECU is also programmed tofilter out any signal which does not fall withincertain frequency ranges.

When the ECU judges that detonation is takingplace, it retards ignition timing until the knockingstops. Timing is then advanced back to calculatedvalue or, if detonation again begins, retarded againuntil detonation is stopped. In this manner, theignition system can be operated at maximumefficiency, on the borderline of detonation, whileavoiding an audible "ping." In the event that the ECUcontinues to sense detonation, timing retard islimited based on a clamp value stored in memory. If

the ECU determines that the knock retard is notfunctional, it will enter a fail-safe mode and fix theretard angle to prevent engine damage.





Altitude Sensing (HAC)

Some TCCS equipped engines like the 3F-E,3VZ-E (Cab and Chassis), and the 7M-GTEincorporate an altitude sensor in the TCCS

system to shorten injection duration whenthe vehicle is operated at higher altitudes.

Because the density of oxygen in theatmosphere is lower at high altitudes, the air volume measured by the air flow meter will

not accurately represent actual oxygenentering the engine. This would result in amixture which is excessively rich, causingemissions and driveability concerns.

The HAC sensor is integrated with the ECUon the 3-FE, 3VZ-E, and 1989 and later 7M-GTE engines. It is remotely mounted behindthe glove box on the '87 and '88 7M-GTESupra. The remotely mounted HAC sensor iswired to the ECU exactly the same as themanifold pressure sensor is wired on D typeEFI. In fact, the HAC sensor circuit iselectrically the same as a manifold pressuresensor circuit. The HAC sensor simplymeasures atmospheric pressure rather thanintake manifold pressure.

The signal from the HAC circuit in the ECU isused to determine the fuel correctioncoefficient to be used after basic injectionhas been calculated. The accompanyinggraph represents how this correction factor affects final injection duration.





Stop Light Switch (STP)

The stop light switch input to the ECU isused to modify the deceleration fuel cutprogram when the vehicle is braking.

Whenever the STIR signal is high (brakepedal is depressed), fuel cutoff andresumption rpm is reduced to improvedriveability characteristics of the vehicle.

In the event the STP signal is lost, fuel cutwill take place at the standard decelerationspeed, causing an objectionable feel whenfuel is canceled.

The STP signal at the ECU will be low aslong as the brake pedal is not applied. Whenthe pedal is depressed, current flows through

the normally open stop light switch to thestop lamps and the ECU, causing the STPvoltage to go high.





The ECU, Process Center of theElectronic Control System

The ECU is an extremely reliable piece of

hardware which has the capability to receiveand process information hundreds of timesper second. At the heart of the ECU is themicroprocessor. It is the processing center of the ECU where input information isinterpreted and output commands areissued. The process and output functions of the ECU can be divided into the following sixareas:

• Fuel Injection Control

• ESA / VAST Spark Advance Control

• Idle Speed Control

• Self Diagnosis

• Related Engine and Emissions Control

• Failure Management (fail-safe and back-up)

Fuel, spark, and failure managementfunctions will be covered individually in thischapter. Idle Speed Control, related enginesystems, emissions control systems, andthe self diagnosis system will be the subjectof chapters 6, 7, 8, and 9, respectively.

ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONS




ECU Power Distributionand EFI Main Relay Circuits

The ECU cannot properly function withoutdependable power feeds and groundcircuits. The power distribution systeminvolves several electrical circuits, protection

devices, relays, and grounds.

ECU Power Feeds

The ECU receives its ignition-switchedpower from the EFI main relay on all of Toyota's EFI systems. In addition to theignition +B power feed, all P7 and TCCSECUs have a direct battery feed, identified asBATT, supplied from either the EFI, STOP, or ECU +B fuse. The EFI main relay +B output

is the power source which feeds the ECUand related engine control circuits. Thedirect battery feed (terminal BATT) serves tomaintain voltage to the ECU keep alivememory when the ignition switch is off.Conventional EFI has no keep alive memorycapabilities and, therefore, uses only anignition switched power feed from the EFImain relay.

Main Relay Circuits

Toyota utilizes several different EFI MainRelaycircuits depending on application. Thesecircuits

can be categorized into four distinct types.1) Dual contact EFI Main Relay, ignition

switch controlled2) Single contact EFI Main Relay, ignition

switch controlled3) Dual EFI Main Relays, ignition switch or

ECU controlled4) Single contact EFI Main Relay, ECU

controlled

Generally speaking, the EFI Main Relaysupplies current to the following major circuits:

• ECU +B and +B1

• Injectors (dual relay or dual contact relayonly)

• Circuit opening relay (power contact andpull-in windings)

• Air flow meter VB circuit (when soequipped)

• Output Actuator Vacuum Switching Valves(VSV)

- Fuel Pressure Up (FPU)

- Exhaust Gas Recirculation (EGR)

- Throttle Opener

• ISC motor/solenoid windings

• Check connector +B terminal





Because the EFI Main Relay supplies batteryvoltage to the +B terminal of the checkconnector when the ignition switch is in therun position, this is an excellent place toperform a quick check of the relay function.

Dual Contact (Single Relay),Ignition Switch Controlled

This EFI Main Relay configuration is used onthe Conventional EFI system. It usesseparate power contacts to supply current tothe fuel injector/ignition circuits and theECU/circuit opening relay circuit. This limitscurrent flow that the ECU power contact musthandle.

This configuration improves the reliability of the relay, reduces possible voltage drop, andalso isolates any inductive noise from theinjectors to the EFI Computer by utilizing thebattery as a large capacitor.

When the ignition switch is turned to the "run"or "start" position, current is supplied to thepull-in winding of the relay. Pull-in ground iswired directly to the vehicle chassis. The onlypower feed to the ECU on this system is the+B circuit.

Single Contact,

Ignition Switch Controlled

This EFI Main Relay circuit is one of the mostpopular power distribution schemes used onlate model TCCS equipped engines. It isused on most applications without a stepper type Idle Speed Control Valve (ISCV).

When the ignition switch is turned to the "run"or "start" position, current is supplied to thepull-in winding of the relay. Pull-in ground iswired directly to the vehicle chassis. ECUBATT voltage is supplied from the STOP fuse

on these applications.





Single Contact, ECU Controlled

This EFI Main Relay circuit is usedexclusively on applications equipped with the

stepper type Idle Speed Control Valve. Thisrelay is powered by the ECU rather than theignition switch to allow control of the relay for approximately two seconds after the ignitionis switched off. This allows the ECU to stepthe ISCV back to engine restart position after ignition power down.

When the ignition switch is turned on or engine cranked, the ECU receives a voltagesignal at the IG SW terminal. This causes the

ECU to supply current from the MRELterminal to the EFI Main Relay pull-inwinding. The pull-in winding is groundeddirectly to the vehicle chassis. ECU BATTvoltage is supplied from the EFI fuse onthese applications.

When the ignition switch is turned off, theECU will maintain current flow through theEFI Main Relay pull-in winding for a fewseconds after power down to allow time toreset the stepper ISCV.

Dual Relays, Ignition Switchor ECU Controlled

This configuration utilizes two separaterelays identified as EFI Main Relay #1 andEFI Main Relay #2. Relay #2 supplies currentto the fuel injector circuit. Relay #1 suppliescurrent to the ECU, Circuit Opening Relay,and other circuits depending on application. If a stepper ISCV is used ('85 and '86 5M-GE),

the ECU will drive relay #1 so the ISCV canbe operated after the ignition is switched off.





ECU Grounds and Quick Checks

No electrical circuit will function normallywithout a dependable ground. Toyota EFIsystems use a redundant ground systemwhich significantly reduces the chance of ground problems; however, this circuitshould never be overlooked whentroubleshooting ECU related systems.

The E2 circuit serves as a signal return or sensor ground. Referring to an EWD, you willnotice that the throttle position sensor, water

and air temperature sensors, and air flowmeter all flow current to ground throughcircuit E2. The ECU supplies a chassisground through the E1 circuit which typicallyterminates somewhere on the engine.

Circuits E01 and E02 serve as grounds for the fuel injector driver circuits. To provide aredundant ground for the ECU, these twogrounds are tied to the E1 circuit through adiode. In the event that the E1 wiring to

chassis is open circuit, E1 circuit currentcould flow through the diode to ground. Thediode serves to prevent voltage spikes fromthe injectors from interfering with other ECUcircuits.

It is not uncommon for many or even all ECUgrounds to terminate at the same point andfasten to the engine with the same fastener.Sometimes a ground fault is due to onefastener being left loose after a serviceprocedure has been performed.

It is a fairly simple task to confirm the integrityof all ECU ground circuits in fairly short order.Two methods can be used to identify andisolate a ground fault; these are the circuitcontinuity check and the voltage drop check.These procedures along with checks of thepower distribution circuits are addressed inexercises 5-1 and 5-2.





Fuel Injection Control





Injector Timing

Injection Timing Control

Injection timing control determines wheneach injector will deliver fuel to itscorresponding intake port. There are threedifferent methods of injector timing used onToyota engines, depending on application.These methods are Simultaneous, Grouped,and Independent injection.

Simultaneous Injection

All injectors are pulsed simultaneously by acommon driver circuit. Injection occurs onceper crankshaft revolution just prior to thecrankshaft reaching TDC cylinder *1. Thismeans that twice per engine cycle one half of the calculated fuel is delivered by theinjectors. This is the simplest and mostcommon injection timing method in use.

Grouped Injection

Injectors are grouped into pairs. The pairsconsist of two consecutive cylinders in thefiring order; each pair is driven by a separatedriver circuit. Four cylinder engines use two

groups, six cylinder engines three groups,and the 1UZ-FE V8 engine uses four groupsof injectors.

Injection is timed to deliver fuel immediatelypreceding the intake stroke for the leadingcylinder in the pair. The entire group ispulsed once per engine cycle, delivering theentire calculated charge of fuel. This timingmethod ensures that fuel does not linger behind the intake valve, thereby, reducingemissions, improving fuel economy andthrottle response.

Independent Injection

Injectors are driven independently andsequentially by separate driver circuits.Injection is timed to deliver the entire fuelcharge just prior to each intake valveopening. This timing method providesoptimum engine performance, emissions,and fuel economy.





Input Signals Required toPulse Injectors

There are three signals which are necessaryto operate the fuel injectors. These are theNe, G, and IGf signals. Inside the ECU, theNe Signal is used to produce an injectionchive signal. The G signal is used todetermine the timing of the injection signals.The IGf signal is monitored for fuel deliveryfail-safe. (With Conventional EFI, the IGsignal is used to produce the injection drivesignal.)

The ECU cannot pulse the injector without anNe signal and will not start or run if thissignal is not present. If the G signal is notpresent while cranking the engine, the ECUwill not be able to identify when to producethe injection signal. The result will be thesame, no injection pulse. If the IGf signal isnot present, the ECU will go into fuel fail-safeby stopping injection pulses.

If, however, the ECU loses the G signal withthe engine running, the engine will continueto run because the timing of injection signalsis locked in once the engine starts.





Injector Operating Modes

There are two injection operating modesused by the ECU, depending on engineoperating conditions. These modes arecalled synchronous and asynchronous.

Synchronous Injection

Synchronous injection simply means thatinjection events are synchronized withignition events at specific crankshaft angles.Synchronous injection is used a greatmajority of the time.

Asynchronous Injection

Asynchronous injection is only used duringacceleration, deceleration, and starting. Itoccurs independently of ignition eventsbased on change in idle contact (IDL) or start

switch (STA) status without regard tocrankshaft angle.





ECU Control of Injector Duration

An Overview of Injection DurationCalculations

Determination of final injection pulse width is the function of a three-step process.

Step 1, Basic Injection Duration

The first step involves calculation of basicinjection duration. Input sensors used inbasic duration calculation are:

• Air Flow Meter (Vs or Ks)

• Manifold Pressure Sensor (PIM)• Engine rpm (Ne)

The ECU calculates basic injection durationbased upon engine speed and air flowvolume. These two inputs consideredtogether establish an engine load factor. TheECU monitors the Air Flow Meter signal or Manifold Pressure Sensor for intake air volume information and the Ne signal for engine speed information.

• As either of these parameters increase,injection duration is increased.

Step 2, Injection DurationCorrection Factors

The second step involves durationcorrections. Input sensors used for injectionduration corrections are:

• Engine Water Temperature (THW)• Intake Air Temperature (THA)• Throttle Angle (VTA or IDL & PSW)• Exhaust Oxygen Content (OX)

Once basic injection duration is calculated,the ECU must modify the injection durationbased on other changing variables. Variablesconsidered in the correction calculation arecoolant and intake air temperature, throttleposition and exhaust oxygen sensor feedback (when operating in closed loop).

• As engine and intake air temperaturesmove from cold to warm, injection durationis reduced.

• As the throttle opens (IDL contact break),injection frequency is momentarilyincreased.

• Fuel injection duration swings back andforth between longer to shorter durations tocorrect conditions detected by the exhaustoxygen sensor.

Step 3, Battery Voltage Correction

The final step is a battery voltage correction.

The input signal used in battery voltagecorrections is: 0 Battery Voltage (+B)

There is an operational delay between thetime the ECU sends the injection signal tothe driver circuit and the actual opening of theinjector. This delay changes with the strengthof the magnetic field around the injector coil.The delay increases as battery voltage falls.

To determine final injection duration, the ECU

corrects for injector opening delay by using abattery voltage correction coefficient.

• The battery voltage correction coefficientincreases injection duration as sensedbattery voltage falls.





ECU Injection StrategyWhile StartingPrime Pulse

Because the rpm and intake air volume

signals are erratic at cranking speed,injection duration calculation is donedifferently while the engine is cranking,compared to all other operating conditions.

Starting Injection Control

To provide accurate fuel injection durationduring cranking periods, the ECU uses aprogram which determines a basic injectionvolume based on engine coolant

temperature. Once a basic injection durationis calculated, corrections are made for intakeair temperature and battery voltage (which istypically low under cranking load).

• Basic injection duration while cranking isincreased at low coolant temperatures.

• Injection duration while crankingis corrected for intake air temperatureby increasing duration at low intake air

temperatures.

• To prime the engine upon initial cranking, allinjectors are pulsed in an asynchronous mode onetime immediately after a G and Ne signal arereceived.

• Injection duration while cranking iscorrected for battery voltage by increasinginjection duration at lower voltage.

The graph represents the basic crankingenrichment strategy used by the ECU. Notethat at temperatures below freezing, basicinjection duration increases drastically toovercome the poor vaporizationcharacteristics of fuel at these temperatures.





Engine Running InjectionDuration Calculation

After Start-up Enrichment

To stabilize the engine immediately after starting, for a short period of time after starting, the ECU supplies extra fuel to theengine to ensure a smooth transition fromcranking to running. The maximumenrichment value is determined by thecoolant temperature signal, THW.

Basic Injection Calculation

Once the engine has stabilized, engine rpminformation and intake air volume

measurements are used to determine basicinjection duration.

• As intake air volume increases, injector duration increases.

• As engine rpm increases, injector frequency increases.

Injection Corrections A correction coefficient is calculated bydetermining the values of the various inputsensors. This correction coefficient is usedto modify the basic injection duration value toachieve a corrected injection duration value.

Correction For Intake Air Temperature The density of intake air varies withtemperature. The colder the air, the denser itbecomes. For this reason, a correctioncoefficient is used for changes in air

temperature.

Referring to the coefficient graph, note that astandard air temperature of 68'F (20'C isused. At this temperature, the correctionfactor is 1.0.

For example, a correction factor of 1.0 meansthat no correction is made from the basic

calculation. A coefficient of 1.1 means thatinjection duration is being increased by afactor of 10% while a coefficient of 0.9 meansthat injection duration is being decreased bya factor of 10%.

• As intake air temperature falls below thestandard temperature, the correctioncoefficient increases and injection durationis increased (and vice versa).





Correction For Coolant Temperature(Warm-up Enrichment)

When the engine is cold, fuel vaporization isrelatively poor until the intake manifoldwarms up. To prevent lean driveability

problems associated with this condition, theECU enriches the air/fuel ratio accordinglybased on engine coolant temperature.

The correction coefficient graph aboveshows a standard value of 158'F (70'C).

• At temperatures below 158'F, basicinjection calculations are increased.

• At extremely cold temperatures, injectionduration can be increased to almostdouble normal warm engine values.

Power Enrichment Correction

When the ECU determines that the engine isbeing operated under moderate to heavyload, it increases injection duration values byup to 20% to 30%. This power enrichment

program is based on information receivedfrom the air flow meter or manifold pressuresensor, the throttle position sensor andengine rpm.

• As engine load increases, injectionduration is increased.

• As engine rpm increases, injectionfrequency increases at the same rate.

Battery Voltage CorrectionBecause of the injector opening delay whichvaries with charging system voltage, the ECUmust modify the corrected injection durationby a battery voltage correction coefficient toachieve a final injection duration value.

The final injection duration determines thequantity of fuel which is delivered to theengine.





Closed Loop Air/Fuel Ratio Correction

Under certain operating conditions, primarilycruise and idle, the ECU corrects theinjection duration value based on signalsfrom the exhaust oxygen sensor. This

feedback correction is necessary to promotebetter vehicle emissions control.

By achieving more accurate fuel metering, theoxygen content of the exhaust stream is heldwithin a very narrow range which supportsthe most efficient operation of the three-way

catalyst (TWC).

Stoichiometry and Catalyst Efficiency

The accompanying graph represents theefficiency of a three-way catalyst system atvarying air/fuel ratios. As the graph clearlyshows, the catalyst is most efficient in anarrow air/fuel ratio range.

The theoretical or ideal air/fuel ratio at whichall tail pipe emissions are best converted isreferred to as stoichiometry. Thestoichiometric air/fuel ratio occurs around14.7 to 1 (14.7 pounds of air for each poundof fuel).

It is important to note that the primary reasonfor using a closed loop fuel control system isto satisfy the requirements of the three-waycatalyst system.





Closed Loop Operation

Closed loop operation simply means that theECU is making air/fuel ratio correctionsbased on oxygen sensor information.

Although the ECU can calculate injection

duration very accurately without usinginformation from the oxygen sensor, closedloop control brings the air/fuel ratio within theextremely narrow operating parameters of the three-way catalyst (TWC).

The oxygen sensor monitors the oxygenconcentrations in the exhaust stream andoutputs a voltage signal to the ECU. Thissignal allows the ECU to determine whether the air/fuel ratio is leaner or richer than thetheoretical value necessary for the bestcatalyst conversion efficiency.

• Exhaust oxygen sensor voltage signalabove 1/2 volt indicates an air/fuel ratioricher than stoichiometry. 'Me ECU willreduce fuel injection duration to correctthis condition.

• Exhaust oxygen sensor voltage signalbelow 1/2 volt indicates an air/fuel ratioleaner than stoichiometry. The ECU willincrease fuel injection duration to correctthis condition.

• During normal closed loop operation, theoxygen sensor signal rapidly switchesbetween these two conditions (at a rate of more than eight times in ten seconds at

2500 rpm). Small injection durationcorrections take place each time the signalvoltage switches from high to low and backagain.

The closed loop correction coefficient rangesfrom 0.8 to 1.2 (that is, +20% from the basicfuel calculation). If the air/fuel ratio goes outof the ECU's range of correction, the ECU willtypically set a diagnostic code and return toopen loop operation.

In a closed loop control system, thecommand corrects the condition.

• Oxygen sensor monitors exhaust condition

• ECU commands injectors to correctcondition

• Oxygen sensor indicates correctionaccuracy

• ECU again commands injectors to correctcondition





Open Loop Operation

Open loop operation means that the ECU isnot correcting the air/fuel ratio based on oxygensensor information. The ECU ignores exhaustoxygen sensor information even if the sensor is

detecting an excessively rich or lean mixture.There are certain operating conditions where it isnot desirable to operate the system in closed loopdue to risk of catalyst overheating and driveabilityconcerns. These conditions are:

• Engine starting• Cold engine operation• Moderate to heavy load operation

In open loop operation, a correction coefficient of 1.0 is used.

Acceleration and Deceleration CorrectionsWhen the engine operating conditions are intransition, either accelerating or decelerating, theinjection volume must be increased or decreasedslightly to improve engine performance and fueleconomy. The input sensor signals used and theenrichment or enleanment strategies used varywith engine application.

Acceleration Enrichment As the engine is accelerated, a momentary leancondition exists as the throttle begins to open (this

is due to the fact that fuel is more dense than air and cannot move into the cylinder as quickly). Toprevent a stumble or hesitation, the ECU uses anacceleration enrichment fuel strategy. When theIDL signal goes from on to off, the ECU delivers anacceleration enrichment fuel pulse.

• As the IDL contact opens, the ECUcommands all injectors to simultaneouslydeliver an extra asynchronous injectionpulse.

On Conventional EFI engines, this pulse is deliveredat the moment the IDL contact breaks. On EFI/TCCSengines, this pulse is delivered synchronous withthe Ne signal which follows the IDL contact break.

Deceleration Fuel CutDuring closed throttle deceleration periods fromhigher engine speeds, fuel delivery is notnecessary. In fact, deceleration emissions and fueleconomy are adversely affected if fuel is deliveredduring deceleration.

To prevent excessive decel emissions and improvefuel economy, the ECU stops injection pulsescompletely during certain deceleration conditions.

• When the IDL contacts close with engine rpmabove a given speed, the ECU cuts injectionoperation completely.

• When the engine falls below the threshold rpm,or when the throttle is opened, fuel injection isresumed.

Referring to the graph, fuel cutoff and resumptionspeeds are variable, depending on coolanttemperature, A/C clutch status, and SIT signal.

• With A/C clutch on, fuel cutoff andresumption speeds will be increased.

• With the stop light switch on, fuel cutoff and resumption speeds will be decreased(some applications only).





Engine Over-rev Fuel Cutoff

To prevent potential engine damage, arevlimiter is programmed into the ECU. Anytime engine rpm exceeds the pre-programmed threshold, the ECU cuts fueldelivery. Once rpm falls below the threshold,fuel delivery is resumed.

Over-rev rpm threshold varies depending onengine design and application but typicallyruns in the 6500 to 7500 rpm range, usuallycutting fuel slightly above the engine's redline rpm.

Vehicle Over-speed Fuel Cutoff

On some vehicles, fuel injection is halted if the vehicle speed exceeds a predeterminedthreshold programmed into the ECU. Fuelinjection resumes after the speed dropsbelow this threshold.





Spark Advance Control

Electronic Spark Advance(ESA)Variable Advance

Spark Timing (VAST)

Introduction To ECUSpark Advance Controls

The Advantage of ECUControlled Spark Timing

To maximize engine output efficiency, theignition spark must be delivered at theprecise moment which will result inmaximum combustion chamber pressure

occurring at about 100 ATDC. The amount of ignition spark advance, or lead time requiredto achieve this, will vary depending on manyfactors.

For example, because fuel bum timeremains relatively constant, spark lead timemust be increased as engine rpmincreases. Because fuel has a tendency todetonate under heavy load conditions, sparklead time must be decreased as manifold

pressure and intake air flow increase.

Engines equipped with Conventional andP7/EFI systems use a mechanical advancedistributor to accomplish changes in sparklead time. The centrifugal (governor) advanceincreases spark lead time as engine rpmincreases, and the vacuum advancedecreases lead time as manifold pressureincreases.

When all of the variables which affectoptimum timing are considered, there aremany more factors which influence requiredspark lead time. The coolant temperature,quality of fuel, and many other engineoperating conditions can significantly impactideal ignition time.

To provide for optimum spark advance under a wide variety of engine operating conditions,a spark advance map is developed andstored in a look up table in the ECU. Thismap provides for accurate spark timingduring any combination of engine speed,load, coolant temperature, and throttleposition while using feedback from a knocksensor to adjust for variations in fuel octane.

Prior to strict emissions and fuel economystandards, mechanical control of sparkadvance was adequate to accomplishreasonable engine performance andemissions control. However, in theautomotive environment of the '90s, adequateis not good enough.





Two ECU Spark Advance ControlSystems Used By Toyota

There are two distinctly different ECUcontrolled ignition systems in use on TCCSequipped engines. These systems are

known as Electronic Spark Advance (ESA)and Variable Advance Spark Timing (VAST).Both systems accomplish the same goal;they provide ideal ignition timing under awide variety of engine operating conditions.

You also learned the mechanics of how theESA and VAST systems signal the igniter and fire the ignition coil. You have learnedthe system hardware. The objective of thislesson is to identify the process the ECUuses to calculate optimum spark advanceangle under a wide variety of operatingconditions. The ECU program whichaccomplishes this is the system software.

ECU Control Of SparkAdvance Angle

Overview Of Advance Angle Calculation Determination of optimum spark advance

angle is the function of a three-step process.

Step 1, Initial Timing Adjustment

The first step involves correct adjustment of initial timing. The input sensor used by theECU to determine initial timing is: 0 StandardCrankshaft Angle (G1, G2, and Ne)

The initial timing adjustment is critical toproper operation of the ECU controlled sparkadvance system. Initial timing is a function of the physical position of the distributor in theengine and becomes the base upon whichall advance functions are added. Once theinitial timing is adjusted properly, it will notchange.

• If distributor position in the engine ischanged, the relationship between Ne andG signals to TDC changes.

• Any deviation from specified initial timingwill cause an equal amount of error in thefinal spark advance angle.





Step 2, Basic Advance Angle

The second step involves calculation of thebasic advance angle. Input sensors used inbasic advance angle calculation are:

• Intake Air Volume (Vs or Ks)

• Intake Manifold Pressure (PIM)

• Engine rpm (Ne)

The basic advance angle is primarily afunction of inputs from the engine rpm andintake air volume sensors. This calculationis equivalent to the combined centrifugal andvacuum advance on a mechanicaldistributor.

• As engine rpm increases, spark angle isadvanced.

• As intake air volume (engine load factor)increases, spark angle is retarded.

Step 3, Corrective Advance Angle

The final step in determining optimum or finalspark advance angle is calculation of corrective advance angle. Input sensors usedin corrective advance angle calculations are:

• Starting Signal (STA)

• Engine Water Temperature (THW)

• Throttle Angle (VTA or IDL & PSW)

• Knock Detection (KNK)

• Altitude (HAC)

• Electronically Controlled Transmission(ECT)

The biggest advantage of ECU controlledspark advance is the system's ability toadjust timing for all possible variables in theideal advance angle equation. The correctiveadvance angle calculation accomplishes thisby fine tuning the advance angle for changesin coolant temperature, engine detonation,transmission shift status, altitude, accessorystatus, and other variables.

• ECU advances spark angle for cold engineoperation and retards for over-temperatureconditions.

• ECU retards spark angle when detonationis detected.

• ECU advances spark angle for high

altitude operation (models equipped withHAC sensor).





ECU Spark AdvanceStrategy While Starting

ESA System

Engine starting: During starting, whenengine speed is below approximately 500rpm (or when STA signal is high), sparkadvance angle (IGt signal) is fixed at initialtiming. A Backup IC located in the ECUgenerates a reference timing signal which isoutput to the microprocessor and the IGt lineto the igniter. The reference signalrepresents base timing and is calculatedbased on inputs from the G1 and Nesensors.

VAST System

Engine starting: During starting, when belowa predetermined rpm, no IGt signal is sentfrom the ECU to the igniter. The ignition coilis driven by the back-up circuit in the igniter atinitial timing.

Engine running: Once the engine starts,timing of the IGt signal is controlled by themicroprocessor in the ECU. Based on inputsfrom various sensors, a basic and correctiveadvance angle are calculated. The final sparkadvance angle consists of the sum of theinitial, basic, and corrective spark advanceangles.

Engine running: Once the engine starts, theECU sends an IGt signal back to the igniter;the ignition coil is driven by this signal atcomputed timing.





ECU Spark Advance StrategyWhile Running

Basic Ignition Advance Angle

The ECU calculates the basic advance angleby evaluating engine rpm and intake air volume signals. These sensors' signalshave the most significant effect on basictiming calculation.

There are other sensor inputs which alsoaffect the basic spark advance angle. The A/Ccompressor clutch signal advances basicspark angle when the IDL contacts are on (onsome engines), and on the 3S-GTE engine,

basic advance angle is retarded if the ECU judges that regular fuel is being used, basedon signals from the engine knock (KNK)sensor.

Corrective Ignition Advance Angle

Engine Temperature Corrections

To improve cold driveability, the ECUadvances spark angle. The ECU considersintake air volume and the status of the IDLcontact to determine how much cold advanceto add to the basic spark calculation.

As the engine temperature approachesovertemp, the ECU will advance spark whenthe IDL contact is on, to prevent overheating.When the IDL contact is off, the ECU willretard spark to prevent detonation. Advanceand retard shown on the graph arecorrections to the basic advance angle.





Fuel Feedback IdleStabilization Correction

To prevent surging due to closed loop air/fuelratio swings, when the IDL contacts are on,the ECU advances timing as lean

commands are sent to the injectors (fuelinjection volume decreased). This very smallamount of advance added to the basicadvance angle serves to stabilize engine idlequality.

Engine Load Idle Stabilization Correction

When engine rpm changes at idle due toincreased load, the ECU adjusts timing tostabilize idle speed. The ECU constantlymonitors and calculates average engine

speed. If the average speed is determined togo below a pre-programmed target rpm, theECU will add advance to the basic sparkangle to help re-establish the target idlespeed.

Detonation Correction

The ECU constantly monitors the signal fromthe knock sensor to determine whendetonation occurs. When detonation issensed, basic advance angle is retarded in

varying degrees, depending on the strengthof the knock sensor signal. Once detonationstops, the ECU gradually cancels the retard,allowing timing to return to the basic advanceangle.

The detonation correction strategy allows theengine to operate at optimum timingregardless of fuel octane, maximizing engineperformance when high octane fuel is used.On some engines, this system only operatesin a closed loop mode under load (vacuumbelow approximately 8 inches of mercury).Other engines operate in ignition closed loopunder all engine load ranges.





ECT (Transmission) Shift Correction

On some applications with integrated ECTcontrols, the Engine and Transmission ECUretards the basic advance angle temporarilyduring gear shifting. This strategy helps

reduce shift shock by reducing engine torquemomentarily, just as the transmission shifts.The amount of retard varies depending onthe status of engine and ECT sensor inputs.

High Altitude Correction

This strategy, which is used only onapplications with High AltitudeCompensation (HAC) capabilities, improvesengine performance and idle quality duringhigh altitude operation by advancing timingover the basic calculated spark angle.

EGR Flow Correction

This strategy advances timing from the basiccalculation when the IDL contact is off andthe ECU is commanding EGR flow. Thiscorrection allows the engine to operate more

efficiently because it resists detonation whenEGR is introduced into the cylinders.

SummaryIt is possible that minor calibration faults inkey system inputs can have a significanteffect on calculated spark advance, resultingin degraded driveability. When performance

problems arise which appear to be the resultof inaccurate timing advance calculation, donot overlook calibration of all relevant inputsensors which influence timing during theaffected driving mode. The best way toconfirm sensor calibration is by becomingfamiliar with, and performing, the ECUStandard Voltage Check procedures.





Purpose of ECU ControlledIdle Speed Control Systems

The Idle Speed Control (ISC) systemregulates engine idle speed by adjusting the

volume of air that is allowed to by-pass theclosed throttle valve. The ECU controls theIdle Speed Control Valve (ISCV) based oninput signals received from various sensors.The system is necessary to providestabilization of curb idle when loads areapplied to the engine and to provide cold fastidle on some applications. The Idle SpeedControl system regulates idle speed under at least one or more of the followingconditions, depending on application:

• Fast Idle• Warm Curb Idle• Air Conditioner Load• Electrical Load• Automatic Transmission Load

Difference BetweenMechanical Air Valvesand ECU Controlled ISCV

The ECU controlled ISC systems addressedin this chapter should not be confused with

the mechanical air valves which wereaddressed in Chapter 2, "Air InductionSystem." The ISC valve is totally controlled bythe ECU based on inputs received from thevarious sensors, and it controls manydifferent idle speed parameters.

The Wax type and Bi-metal mechanical air valves are used only to regulate cold enginefast idle and are not ECU controlled.

There are some engines which utilize amechanical air valve, for cold fast idle control,in combination with an ECU controlled ISCVacuum Switching Valve (VSV) to controlwarm curb idle.

ENGINE CONTROLS PART #3 - IDLE SPEED CONTROL




Four Different ECU ModulatedIdle Speed Control Systems (ISC)

There are four different types of ECU con-

trolled ISC systems used on Toyota engines.These systems are referred to as:

• Stepper motor type

• Rotary solenoid type

• Duty control ACV type

• On-off control VSV type

Step Motor Type ISC Valve

The Step Motor type ISCV is located on theintake air chamber or throttle body. Itregulates engine speed by means of astepper motor and pintle valve which controls

the volume of air by-passing the closedthrottle valve. The ISCV throttle air by-passcircuit routes intake air past the throttle valvedirectly to the intake manifold through avariable opening between the pintle valve andits seat.

The valve assembly consists of four electricalstator coils, a magnetic rotor, a valve andvalve shaft. The valve shaft is screwed intothe rotor so that as the rotor turns, the valveassembly will extend and retract.





The ECU controls movement of the pintlevalve by sequentially grounding the four electrical stator coils. Each time current ispulsed through the stator coils, the shaftmoves one 44 step." Direction of rotation isreversed by reversing the order with whichcurrent is passed through the stator coils.

The pintle valve has 125 possible positions,from fully retracted (maximum air by-pass) tofully extended (no air by-pass). In the eventthat the ISCV becomes disconnected or inoperative, its position will become fixed atthe step count where it failed. Because thestepper idle speed control motor is capableof controlling large volumes of air, it is usedfor cold fast idle control and is not used incombination with a mechanical air valve.





Primary Controlled Parameters

Initial Set-up

Engines equipped with the stepper type ISCVuse an ECU controlled EFI main relay which

delays system power down for about twoseconds after the ignition is turned off.During these two seconds, the ECU fullyopens the ISCV to 125 steps from seat,improving engine stability when it is started.This reset also allows the ECU to keep trackof the ISCV position after each engine restart.

Engine Starting Control When the engine is started, rpm increasesrapidly because the ISCV is fully open. ThisISCV position is represented by point A onthe graph, 125 steps from seat.

When 500 rpm is reached, the ECU drivesthe ISCV to a precise number of steps fromseat based on the coolant temperature attime of start-up. This information is stored ina look up table in the ECU memory and isrepresented by point B on the graph.

Engine Warm-up Control

As the engine coolant approaches normaloperating temperature, the need for cold fastidle is gradually eliminated. The ECUgradually steps the ISCV toward its seatduring warmup. The warm curb idle positionis represented by point C on the graph. By

the time the coolant temperature reaches176'F (80'C), the cold fast idle program has

ended.

Feedback Idle Speed Control

The ECU has a pre-programmed target idlespeed which is maintained by the ISCVbased on feedback from the Ne signal.Feedback idle speed control occurs any timethe throttle is closed and the engine is atnormal operating temperature. The target idle

speed is programmed in an ECU look uptable and varies depending on inputs fromthe A/C and NSW signals. Any time actualspeed varies by greater than 20 rpm fromtarget idle speed, the ECU will adjust the ISCvalve position to bring idle speed back ontarget.





Engine Load/Speed ChangeEstimate Control

To prevent major loads from changingengine speed significantly, the ECUmonitors signals from the Neutral Start

Switch (NSW) and the Air Conditioner switch(A/C) and re-establishes target idle speedsaccordingly. ISCV position is adjusted veryquickly as the status of the A/C or NSWinputs change. Before a change in enginespeed can occur, the ECU has moved theISCV to compensate for the change inengine load. This feature helps to maintain astable idle speed under changing loadconditions.

The following chart shows typical target idlespeeds which can be found in New Car Feature books. These speed specificationscan be useful when troubleshootingsuspected operational problems in the steptype idle speed control system or relatedinput sensor circuits.

Other Controlled Parameters

Electrical Load Idle-up

Whenever a drop in voltage is sensed at theECU +B or IG S/W terminals, the ECU

responds by increasing engine idle speed.This strategy ensures adequate alternator rpm to maintain system voltage at safeoperational levels.

Deceleration Dashpot Control

Some ECUs use a deceleration dashpotfunction to allow the engine to gradually idledown. This strategy helps improveemissions control by allowing more air intothe intake manifold on deceleration. Thisextra air is available to mix with any fuel whichmay have evaporated during the low manifoldpressure conditions of deceleration.

Learned Idle Speed Control

The idle speed control program is based onan ECU stored look up table which lists pintlestep positions in relation to specific enginerpm values. Over time, engine wear and other variations tend to change theserelationships. Because this system iscapable of feedback control, it is alsocapable of memorizing changes in therelationship of step position and engine rpm.The ECU periodically rewrites the look uptable to provide more rapid and accurateresponse to changes in engine rpm.





The Rotary Solenoid ISCV is mounted to thethrottle body. This small, lightweight andhighly reliable valve controls the volume of intake air which is allowed to by-pass theclosed throttle valve. Air volume control isaccomplished by means of a movable rotaryvalve which blocks or exposes the air by-pass port based on signals received fromthe ECU.

Because the Rotary Solenoid ISCV has largeair volume capability, it is used to control coldfast idle as well as other idle speedparameters. Although this ISCV is not usedin combination with a mechanical air valve,models equipped with air conditioning dorequire the use of a separate A/C idle-updevice.

The valve assembly consists of two electricalcoils, a permanent magnet, a valve and valveshaft. A fail-safe bi-metallic coil is fitted to theend of the shaft to operate the valve in theevent of electrical failure in the ISCV system.





The ECU controls movement of the valve byapplying a 250 Hz duty cycle to coils T1 andT2. The electronic circuitry in the ECU isdesigned to cause current to flow alternatelyin coil T1 when the duty cycle signal is low

and in coil T2 when the signal is high. Byvarying the the duty ratio (on time comparedto off time), the change in magnetic fieldcauses the valve shaft to rotate.

As duty ratio exceeds 50%, the valve shaftmoves in a direction that opens the air by-pass passage. At a duty ratio less than 50%,the shaft moves in a direction which closesthe passage. If the electrical connector is

disconnected or the valve fails electrically,the shaft will rotate to a position whichbalances the magnetic force of thepermanent magnet with the iron core of thecoils. This default rpm will be around 1000 to1200 rpm once the engine has reachednormal operating temperature.

Rotary ISCV Controlled Parameters

Engine Starling, Warm-upand Feedback Control

When the engine is started, the ECU opens

the ISCV to a pre-programmed positionbased on coolant temperature and sensedrpm. The higher the commanded rpm, thelonger the duty ratio will be. As the engineapproaches normal operating temperature,engine speed is gradually reduced.

Once the engine is fully warmed up, the ECUutilizes a feedback idle speed control strategywhich functions identically with the stepper motor ISC system. Different target idlespeeds are established depending on thestatus of load sensor inputs.

Turbo Charger Idle Down Control

On the 3S-GTE engine, the ISCV remains at ahigher idle air by-pass rate for a short periodof time after high speed or heavy loadoperation. This strategy prevents damage tothe turbocharger center shaft bearings bymaintaining an elevated engine oil pressure.

All other controlled parameters for the RotarySolenoid ISC system are the same as thewith the Stepper type ISCV. Idle loadstabilization is maintained when input fromthe neutral safety switch (NSW), headlights or rear window defogger (ELS) indicateadditional engine load.

As with the Stepper type ISC system, theRotary Solenoid system utilizes a learned

idle speed control strategy. The ECUmemorizes the relationship between enginerpm and duty cycle ratio and periodicallyupdates its look up tables. Both systemsutilize current supplied by the BATT terminalof the ECU to retain this learned memory. If the battery is disconnected, the ECU mustrelearn target step positions and duty cycleratios.





Duty Control Air Control Valve (ACV) ISC

The Duty Control ACV is typically mounted onthe intake manifold. It regulates the volumeof air by-passing the closed throttle valve by

opening and closing an air by-pass. Valveopening time is a function of a duty cyclesignal received from the ECU.

The ACV is incapable of flowing largevolumes of air; therefore, a separatemechanical air valve is used for cold fast idleon engines equipped with this system.

The Duty Control ACV consists of anelectrical solenoid and a normally closed(N/C) valve which blocks passage of fresh air from the air cleaner to the intake manifold.The ECU controls the valve by applying a 10Hz variable duty ratio to the solenoid, causingthe valve to pass varying amounts of air intothe manifold. By increasing the duty ratio, theECU holds the air by-pass circuit openlonger, causing an increase in idle speed.

Duty Control ACV Controlled Parameters

Starting and Warm Curb Idle

When the STA signal to the ECU is on, theECU cycles the VSV at a 100% duty cycle toimprove startability. The ACV does not haveany effect on cold fast idle or warm-up fastidle speed.





When the engine has reached normaloperating temperature, and the IDL contact isclosed, the ECU uses a feedback idle speedcontrol strategy to control warm curb idlespeed. When loads are applied to the engine

from the automatic transmission or electricaldevices, the ECU adjusts target idle speedsaccordingly. When the IDL contact is open or any time the Air Conditioning (A/C) signal tothe ECU is on, the ECU maintains a constantduty cycle ratio to the ACV, allowing a fixedamount of by-pass air to flow.

Diagnostic Mode

When the TCCS system enters diagnosticmode (TE1 shorted to E1), the ECU will drivethe ACV to a fixed duty cycle ratio regardlessof engine operating conditions. Curb idleadjustment on engines equipped with thisISC system is performed in diagnosticmode. For more information on curb idleadjustment procedures, refer to Appendix C.

On-Off Control Vacuum SwitchingValve (V-ISC System)

The simple On-Off Vacuum Switching Valve(VSV) ISC system is controlled by signalsfrom the ECU or directly by tail lamp and rear

window defogger circuits. The VacuumSwitching Valve (VSV) is typically located onthe engine (often under the intake manifold)or in the engine compartment, controlling afixed air bleed into the intake manifold.

The valve is a normally closed (N/Q designwhich is opened when current is passedthrough the solenoid windings. Unlike mostECU controlled circuits which are groundcircuit driven, the ECU controls this VSV bysupplying current to the solenoid coil whenpre-programmed conditions are met.

Additionally, current can be supplied to thesolenoid from the rear window defogger or taillight circuits by passing through isolationdiodes.





The VSV allows only a small amount of air toby-pass the closed throttle valve when it isopen, increasing engine speed by about 100rpm when energized. This ISC system doesnot control cold fast idle, and engines

equipped with the system use a mechanicalair valve for cold engine fast idle.

On-Off Control VSV Controlled Parameters

Engine Starting and Warm Curb Idle Control

The solenoid is energized by the ECUwhenever the STA signal is on and for a short

period of time thereafter to improvestartability. Additionally, when the IDL contactis closed, the ECU will energize the solenoidwhenever engine speed drops below a pre-determined rpm.

Automatic Transmission Idle-up Control

The ECU will energize the VSV for severalseconds after shifting the transmission fromPark or Neutral to any other gear to stabilizeengine speed during the transition fromunloaded to loaded conditions.

Electrical Load Idle-up

Referring to the electrical schematic, the VSVreceives current directly from the tail lampand rear window defogger circuits throughisolation diodes whenever these circuits areoperating.

Diagnostic Mode

Whenever the TE1 circuit is grounded, theECU is prevented from actuating the V-ISCVacuum Switching Valve. This inhibit featureis useful during diagnostic and other serviceprocedures. It is important to note that thiswill not prevent the VSV from energizing whenthe defogger or tail lamp relays areenergized.





Input Sensors Affecting IdleSpeed Control Output

Major Impact Sensors

The following input signals to the ECU havea major impact on the output commandssent to the Idle Speed Control Valve.

Engine RPM (Ne)

The Ne signal is one of the most criticalinputs for proper operation of the ISCsystem. This sensor supplies the enginerpm feedback used to determine whether actual rpm equals target rpm.

Throttle Position (IDL)

The Idle Speed Control System is functionalonly when the throttle is closed and thevehicle is not moving. The ECU monitors theIDL signal to determine when to outputcommands to the ISC actuator. When the IDLcontact is closed and the vehicle is notmoving, the ECU outputs signals to the ISCV.When the IDL contact is open, the ISCsystem is not functional. Without an accurate

signal from the IDL contact, the ISC systemcannot function normally.

Engine Coolant Temperature (THW)

The idle speed control program look uptables list different engine rpm targetsdepending on coolant temperature for theStep and Rotary ISC systems which controlcold fast idle. The ECU uses the THW signalto determine engine coolant temperature for accurate control of idle speed under all

engine temperature conditions.

Vehicle Speed (SPD)

The ISC system is not functional when thevehicle is moving. The ECU monitors theSPD signal from the vehicle speed sensor todetermine when to operate the ISCV. If theIDL contact is closed and no SPD signal isdetected, the ECU will output a signal to theISCV.

Vehicle Speed Sensor Operation

The ECU expects to see a digital signal of four pulses for each speedometer cablerevolution when the vehicle is moving. Thevehicle speed sensor (VSS) provides this

signal.

There are two different types of vehicle speedsensors used to supply information to theengine ECU. Although these sensors differ indesign, the final output signal to the ECU isthe same for both, four digital pulses per cable revolution.

Reed Switch Type: The Reed Switch vehiclespeed sensor is located in the combinationmeter assembly and is operated by thespeedometer cable. The sensor consists of an electrical reed switch and a multiple polepermanent magnet. As the the speedometer cable turns, the permanent magnet rotatespast the reed switch. The magnetic flux linescause the contacts to open and close as theypass. The magnet is arranged so that thesensor contacts open and close four times

for each revolution of the sensor.





Photocoupler Type: The Photocoupler vehicle speed sensor is also located in thecombination meter and operated by thespeedometer cable. The sensor consists of a photocoupler circuit and a 20-slot trigger

wheel.

The photocoupler circuit is a simpleelectronic device which uses a photo-transistor and a light emitting diode (LED) togenerate a digital electrical signal (seearticle on Karman vortex air flow meter inChapter 5 for operation theory of photocoupler circuit). As the slotted trigger

wheel moves between the LED andphototransistor, it intermittently blocks andpasses light at the photo-transistor. Whenthe wheel blocks the LED, the transistor turns off and when the wheel passes thelight, the transistor turns on.

With 20 slots, this sensor generates 20digital pulses per speedometer revolution. Anelectronic circuit in the combination meter conditions this signal into four pulses whichare sensed by the SPD circuit in the ECU.

Electrically, both the Reed type andPhotocoupler type speed sensors work thesame. The sensor is, in fact, a switch. Byswitching on and off, the sensor pulls areference voltage from the ECU to ground.The resulting voltage drop is monitored bythe ECU as the SPD signal.





Minor Impact Sensors

Neutral Start Switch (NSW)

The Neutral Start Switch input to the ECU isused for ISC control as well as having an

influence, although minor, on the fuel deliveryprogram. As it relates to the ISC system, thisinput is used to determine when to increaseidle speed for Engine Load/Speed ChangeEstimate strategy.

The NSW signal at the ECU will be low (lessthan 1 volt) as long as the neutral start switchis closed, as it will be with the gear selector in Park or Neutral. This low signal is causedby the voltage drop across R1 which has arelatively high resistance compared to thestarter and circuit opening relay coils. Whenthe transmission is shifted into any gear, theneutral start switch opens, causing a halt incurrent flow through the NSW circuit. Thiscauses an increase in signal voltage at theNSW terminal of the ECU.

In the event this signal malfunctions, the ECUwill use the wrong target idle speed for ingear operation and a distinct drop in idle rpmwill be noticed as the transmission is shiftedfrom Park or Neutral to any drive gear.

Engine Cranking Signal (STA)

The STA signal is used by the ECU to allowadditional air to enter the intake manifoldwhile cranking the engine. Additionally, it isused to determine when to enrich injectionfor starting and when to operate the FuelPressure-Up (FPU) system. In the event thatthe STA signal malfunctions, the engine maybe difficult to start.

The STA signal at the ECU will be low at alltimes except while the engine is cranking.While cranking, the STA signal goes high(cranking voltage) as current flows throughthe closed ignition switch and neutral startswitch contacts.





Air Conditioning Compressor Signal (A/C)

The A/C signal to the ECU is used todetermine when the air conditioningcompressor is loading the engine. Thesignal is used primarily as an indication to

increase ISC air flow to stabilize idle speed.The A/C input is also used by the ECU tomodify ignition timing and deceleration fuelcut parameters during compressor operationperiods. When the A/C signal is high and theIDL contact is closed, the ECU limitsminimum ignition spark advance angle.

Additionally, decel fuel cut rpm is increased.In the event that this signal malfunctions, idlequality may suffer and driveability duringdeceleration could be affected.

The A/C signal at the ECU will be high anytime the compressor clutch is energized.When power is removed from the clutchcircuit, it is simultaneously removed from the

A/C input at the ECU.

Electrical Load Sensor (ELS)

The ELS circuit signals the ECU whensignificant electrical load has been placed onthe charging system from the vehicle lightingor rear window defogger systems. The ECU

uses this information to increase the dutycycle ratio on the Rotary ISC Valve, therebymaintaining a stable idle speed.

The ELS signal at the ECU will be low aslong as the tail lamps and rear windowdefogger are off. When either of theseaccessories are turned on, current flows tothe accessory and through an isolation diodeto the ECU. When either accessory is on, thesignal at the ECU will go to battery voltage.





System Diagnosis andTroubleshooting

An Overview of the Self Diagnostic System

The ECU on all P7 and TCCS engines has aself diagnostic system which constantlymonitors most of the electronic controlsystem's input circuits. When the ECUdetects a problem, it can turn on the checkengine light to alert the driver that a faultexists in the system. At the same time, theECU registers a diagnostic code in its keepalive memory so that the faulty circuit can beidentified by a service technician at a latertime.

if the circuit fault goes away, the checkengine light will go off. However, thediagnostic code will remain in the ECUmemory even after the ignition switch isturned off. For most engines, the contents of the diagnostic memory can be checked byshorting check connector terminals T (or TE1) and E1 together and counting thenumber of flashes on the check engine light.

After the problem has been repaired, thetechnician can clear the diagnostic systemby removing the power from the ECU BATTfeed.

Fault Detection Principles The ECU fault detection system isprogrammed to accept sensor signal valueswithin a certain range to be normal, andsignals outside of that range to be abnormal. The normal signal range used to diagnose

most sensor circuits covers the entireoperating range of the sensor signal. As longas the signal value falls within this range, theECU judges it to be normal. As a result, it ispossible for the sensor to generate a signalwhich does not accurately represent theactual operating condition and not bedetected as a problem by the ECU.

The fault detection range graph shows typical THW signal parameters. Point A is normaloperating temperature and falls within thefault detection normal range. Point Brepresents the freezing point of water andalso falls in the normal range. If the engine isat normal operating temperature but the THWsensor signals the ECU that the coolanttemperature is freezing (point B), the enginewill operate excessively rich and may not start

when hot. Because point B falls within thenormal range, the ECU will not recognize thisas a problem. No diagnostic code will be setfor this problem.

Limitations of the Self Diagnostic System

The self diagnostic system provides anexcellent routine to direct the technician to theheart of an electronic control systemproblem. There are however, severallimitations which must be kept in mind when

troubleshooting.

• The ECU must see a signal in anabnormal range for more than a givenamount of time before it will judge thatsignal to be faulty. Therefore, manyintermittent problems cannot bedetected by the ECU.

ENGINE CONTROLS PART #4 - DIAGNOSIS




• When the ECU stores a diagnosticcode, the code indicates a problemsomewhere in the sensor circuit, notnecessarily in the sensor itself Furthertesting is always required to properly

diagnose the circuit.

• Not all circuits are monitored by theECU. J ust because the ECU generatesa normal code does not mean that thereare no problems within the electroniccontrol system.

• Occasionally, diagnostic codes can beset during routine service procedures orby problems outside the electroniccontrol system. Always clear codes andconfirm that they reset prior to circuittroubleshooting.

Check Engine Lamp Functions The check engine lamp serves two functionsin the self diagnostic system, depending onthe status of the T terminal. When the Tterminal is off (not shorted to E1) the checkengine light goes on to warn the driver whena major problem is detected in the electroniccontrol system. When the T terminal is on(shorted to E1) the check engine lightdisplays stored diagnostic codes for use bythe technician.

VF (Voltage Feedback)Terminal Function The VF terminal also serves two diagnostic

functions depending on the status of the Tterminal. When the T terminal is off, the VFterminal voltage represents learned value correction factor. When the T terminal is on,the VF terminal will either display anemulated oxygen sensor signal (throttleopen, IDL contact off) or indicate whether adiagnostic code is stored in the ECU memory(throttle closed, IDL contact on).





Four Systematic StepsIn Diagnos isSimply stated, there are four steps to followwhen performing a methodical diagnosis

from start to finish. Using this systematicapproach will generally lead to reduceddiagnostic time and a higher degree of success. The four steps are listed asfollows.

• Routine Quick Checks• Use of the Self Diagnostic System• Troubleshooting by Symptom• Quality Control Check

Routine Quick Checks

This step in diagnosis includes confirmationof the problem and routine mechanical andelectrical engine checks.

Confirmation of the customer concern is anexcellent place to begin any diagnosis. It isimportant to gather and analyze as muchinformation as the customer can supply and,if the check engine warning lamp is on, toretrieve and record the diagnostic codes.

The conditions of the battery and chargingsystem are critical to the proper operation of the electronic control system. Both should beroutinely checked by measuring crankingand engine running battery voltage prior toproceeding with diagnosis.

Depending on the problem or driveabilitysymptom indicated, the following checksshould be conducted under the hood:

• Inspection of the engine's mechanical condition(i.e., audible cranking rhythm and visual ignitionsecondary condition).

• Brief inspection of accessible electrical, vacuumand air induction system duct connections.

• Locate and inspect the condition of the ECU maingrounds.

• Inspect for leakage in the EGR and PCV valves.• Inspect for unwanted fuel entering the intake

manifold from the EVAP system.

The entire routine quick check procedure canbe performed in less than ten minutes andwill often save an hour or more of unnecessary diagnostic time.

Use of the Self Diagnostic System Once youare satisfied that there are no routineproblems causing the customer concern,use of the self diagnostic system is in order. This system is available on all P7 and TCCSequipped engines and is capable of indicating if certain faults exist in ECUmonitored circuits.

The P7 systems have limited diagnosticcapabilities and can only display sevendiagnostic codes, including a system normalcode. This system will only indicate a fault if the circuit is open or shorted to ground.

Late model TCCS systems have moresophisticated diagnostics which monitormore ECU related circuits with as many as21 or more diagnostic codes. The latest TCCS ECUs have some special capabilitieswhich make them more useful in diagnosisand prevent the check engine warning lightfrom becoming a source of customerdissatisfaction.

• To allow the diagnostic system to find moresystem faults, the electrical parameters whichthe ECU uses to set a diagnostic code are alteredto find sensor performance faults like oxygensensor degradation.

• Some minor TCCS system fault codes will set adiagnostic code in the ECU keep alive memory butwill not turn on the check engine light andunnecessarily alarm the customer.

• To prevent false indication of certain systemfaults, some ECUs are programmed to use a two-trip detection logic which prevents the checkengine light from illuminating, or certain codesfrom setting, until the problem has duplicateditself twice, with a key off cycle in between.

• Some ECUs have a special diagnostic TEST modewhich causes the ECU to narrow its diagnosticparameters for the technician, thereby, makingtroubleshooting intermittent problems easier.





Procedures toRetrieve Trouble Codes There are several different types andlocations of diagnostic connectors which are

used to trigger and, in some cases, readdiagnostic code output from Toyota EFIengines. All late model TCCS applications,from 1988, use a multiple terminaldiagnostic check connector . Earlier modelsuse this same multiple terminal or a two-terminal check connector, all located underthe hood.

The procedure to examine the ECU memoryfor diagnostic codes is typically very simpleregardless of which vintage engine beingdiagnosed. All engines equipped with self diagnostic systems have one terminal of the

check connector identified as T or TE1. Whengrounded, this terminal triggers the self diagnostic feature of the ECU. The E1 groundcircuit is also located in the check connector.

To enter engine diagnostics:

• Locate the check connector under the hoodand identify the T (TE1 on late model TCCS) and E1 terminals.

• Turn the ignition switch to the "on" positionand make sure that the check engine lightis on.

• Confirm that the throttle is closed (IDLcontact on).

• J umper check connector terminals T (TE1)to E1.





When the T terminal is grounded with theignition switch in the "on" position, the ECUsees the voltage at terminal T go low. Lowvoltage on T causes the ECU to enterdiagnostic mode, producing diagnostic

codes on the check engine light. On '83through '85 Cressida and Supra models, thecheck engine light does not flash diagnosticcodes. An analog voltmeter must be used toread the codes from the VF terminal of theEFI Service Connector.

Depending on the vintage of the systembeing tested, the codes will be displayed ineither one or two digit format. It is important torefer to the proper repair manual for specificinformation about diagnostic connector

location, code format, and proper proceduresfor the vehicle you are troubleshooting.





Super Monitor Display: On some 1983through 1987 Cressida and Supra models, aSuper Monitor trip computer was offered asoptional equipment. This display can beused to read diagnostic codes by simply

pressing and holding the monitor "Select"and "Input M" keys together, for threeseconds, with the ignition switch in the "on"position. When the "DIAG" message appearson the display, pressing and holding the"Set" key for three seconds will put the TCCSsystem into diagnostic mode. The displaywill indicate any diagnostic codes stored inthe ECU's keep alive memory.

Once Diagnostic Codes Are Retr ievedOnce diagnostic codes have been retrievedfrom the ECU keep alive memory, it isadvisable to erase the codes and road testthe vehicle. 'Me purpose of this procedure isto confirm that the problem(s) will be presentduring your diagnosis.

If the diagnostic code re-occurs, the problemcan be considered a hard fault andtroubleshooting will be routine. If thediagnosis code does not re-occur, theproblem is either intermittent or wasinadvertently stored during a previous serviceprocedure.

If an intermittent fault is suspected, aphysical check of the indicated circuit mustbe performed by flexing connectors andharnesses at likely failure points whilemonitoring the circuit with a multimeter or

oscilloscope. If the problem is temperature,vibration, or moisture related, the circuit canbe heated, lightly tapped, or sprayed withwater to simulate the failure conditions.Attempting to troubleshoot intermittentproblems using the normal diagnosticroutines will likely result in a misdiagnosisand wasted time.

Erasing Long Term Memory The procedure to erase stored diagnosticcodes is as simple as removing a fuse ordisconnecting the battery negative terminalfor at least thirty seconds. Fuse removal isthe method of choice because it will notdisturb any other computer memories in thevehicle (ETR radio stations, trip computerdata, etc.)

The proper fuse to remove depends on

application but will always be the one whichfeeds the ECU BATT terminal. The followingfuses supply BATT power distribution to theECU keep alive memory: EFI, STOP, or onsome P7 applications, ECU +B.





Monitored andNon-monitored Circui tsAlthough the newer TCCS self diagnosticsystem is getting more sophisticated every

model year, there are still many electroniccontrol system circuits which the ECU doesnot monitor. Generally speaking, most inputsensors are monitored for faults, but mostoutput actuators are not. Exceptions to thisare the Neutral Start Switch (NSW) andPower Switch (PSW)* input signals whichare not monitored. Codes 25 and 26 monitorthe air/fuel ratio rather than the status of aparticular circuit.

Troubleshooting After Code Retr ieval The diagnostic code leads only to a circuitlevel diagnosis. A pinpoint test of the circuitindicated will be required to isolate theproblem down to the component or wiringlevel.

To find the appropriate diagnostic procedureto follow:

• Refer to the last column of the repairmanual "Diagnostic Codes" list.

• This will lead to one or more"Troubleshooting with aVoltmeter/Ohmmeter" diagnostic chartswhich will facilitate circuit diagnosis.

• This may also lead to an "Inspection of Component" procedure which will facilitatediagnosis of the sensor or actuator in thecircuit.

But what if you do not have a diagnostic codeto help lead you to the cause of the customercomplaint? What do you do next? Before weaddress the third step in the systematicdiagnostic approach, the subject of aninoperative self diagnostic system must beaddressed.





No Self Diagnostic SystemOutput (Use of Diagnostic Circui tInspection Schematic) There are several conditions which could

cause the self diagnostic system tomalfunction. In the event the check enginelight does not work or if the system will notflash diagnostic codes, it will be impossibleto make an accurate diagnosis of theelectronic control system. Following aresome suggestions to help troubleshoot thiscondition if it is encountered.

Normal Operation The following sequence of events shouldoccur when diagnostics are functioningnormally:• With the ignition switch in the "on" position,

the check engine fight should be on steady.• When the T circuit is grounded, the check

engine light should flash a normal code if all monitored circuits are in proper workingorder.

• If a fault exists in any monitored circuit, theappropriate diagnostic code should bedisplayed. If there is more than one codestored in the ECU keep alive memory,codes will be displayed in numericalsequence from lowest to highest.

• Diagnostic codes will continue to repeatuntil the key is turned off or the T circuitground is removed.

Abnormal OperationIn the event the self diagnostic system is notfunctioning normally, it will likely exhibit one of the following symptoms.

1) Check engine light fails to come on atpower up (key on, engine off, T circuitopen).

2) Check engine light will not flash code

when T circuit grounded (T jumpered toE1), check engine lamp stays on or staysoff.

These conditions must be corrected beforefurther diagnosis can be performed! Thefollowing charts will help to direct you toperform a "Diagnostic Circuit Inspection."





At this stage in your diagnosis, you may havealready diagnosed the problem and areready for repair and a quality control check. If the problem has not yet been identified, youare ready for the next diagnostic step.

Troubleshooting By SymptomWhen the self diagnostic system fails toindicate a problem with the electronic controlsystem (normal code displayed), there aretwo possibilities left. Either there is aproblem in the electronic control systemwhich the ECU is not capable of detecting orthe problem lies outside of the electroniccontrol system entirely. In either case, the"Troubleshooting" section of the repairmanual will help you locate the appropriatediagnostic routine to quickly isolate theproblem cause.

The third step in a systematic diagnosisrequires use of the "Troubleshooting" and ccVoltage at ECU Wiring Connectors" sectionsof the repair manual. Based on the symptomthe vehicle exhibits, these manual sectionswill lead you to the diagnostic routine which

will assist in solving the problem.

Voltage at ECU Connector Checks The self diagnostic system is not capable of detecting sensor circuits which are feedingout of range information to the ECU. By usingthe Voltage at ECU Wiring Connectors chart,measured voltage signals at the ECU can becompared to standard vol tage values listed

in the repair manual. Signals which are out of the normal range can be identified and thecause diagnosed by referring to the far rightcolumn of the chart; this will lead to theappropriate pinpoint test to perform.

In the event that all listed values fall within anormal range, the symptom charts in therepair manual should be consulted. Startingwith new models introduced after '90, repairmanuals include a comprehensivetroubleshooting matrix that replaces thesymptoms charts. Beginning with '92 repairmanuals, this matrix is located at thebeginning of the Emissions (EM) section of the repair manual.

Using the Symptom Chartsand Troubleshooting Matrix The most important part of troubleshooting bysymptom is to identify the symptomaccurately. An accurate description of theproblem will ensure that the appropriatediagnostic routines will be selected. Basedon the symptom chosen, a series of testingroutines are available to assist in pinpointing

the problem area.

These test routines address items within theelectronic control system as well as areasoutside the system which could cause thesymptom chosen. The technician'sknowledge and experience will be his guideto which tests to perform first and which teststo disregard in any particular situation.





Quality Control Check andConfirmation of Closed Loop The final step in any diagnosis and repair isa quality control check to confirm that the

original customer complaint has beencorrected and that the system is functioningnormally. In the case of the engine electroniccontrol system, the Quality Control Checkshould consist of the following items:

• Clear any stored diagnostic codes.

• Confirm closed loop operation.

• Confirm normal air/fuel ratio calibration.

• Confirm codes do not reset.

Three of these confirmations can beperformed using the VF terminal of the checkconnector.

Using the VF Terminal As A ClosedLoop and Air/Fuel Ratio Moni tor The VF terminal serves as a closed loopmonitor, allowing the technician to track the

oxygen sensor activity and confirm closedloop operation.

To Use the VF Terminal as aClosed Loop Monitor

• T terminal must be on (shorted to E1).

• IDL contacts must be off (throttle open).

When these conditions have been satisfied,the voltage signal on the VF terminal willimitate the oxygen sensor signal. Wheneverthe oxygen sensor signal is high, indicating arich exhaust condition, the VF terminalvoltage will be 5 volts. When the oxygensensor signal is low, indicating a leanexhaust condition, the VF terminal voltage will

be 0 volts.

At 2500 rpm, oxygen sensor switching shouldoccur a minimum of eight times in tenseconds if the closed loop system isoperating normally. To test, the engine mustbe fully warmed up and run at 2500 rpm forone minute to ensure the oxygen sensor hasreached operating temperature.





To Use the VF Terminal toConfirm Air/Fuel Ratio

• T terminal must be off (not grounded).

Under this condition, the VF voltagerepresents the learned value correctionfactor to fuel injection duration. As youlearned in Chapter 5, final injection durationis the sum of basic injection plus injectioncorrections. Learned value is simply anothercorrection factor which is used to bring thecorrected air/fuel ratio as close to thestoichiometric air/fuel ratio as possible.

The ECU fuel injection duration program isthe same for every engine; however, eachengine is a little bit different from the next. The purpose of the learned value correctionis to tailor the standard fuel injection duration

program to each individual engine. Theinjection duration calculation, before oxygensensor correction, is the ECU's best guess ata stoichiometric air/fuel ratio. The oxygensensor correction fine-tunes injectionduration precisely to 14.7 to 1. The learnedvalue correction factor ensures that oxygensensor corrections do not become too largeto manage.

In this mode, the VF voltage signal will be atone of five different steps (three steps on Dtype EFI) depending on how close thecalculated air/fuel ratio (before oxygen sensorcorrection) is to stoichiometry. With theengine operating in closed loop, learnedvalue VF should be somewhere in the 1.25 to3.75 volt range with a nominal value of 2.5volts.

Generally speaking, a lower voltage indicatesthe ECU is decreasing fuel to correct forsome long term rich condition. Examples of conditions which could cause low learnedvalue VF:

• Crankcase diluted with fuel

• Loaded evaporative canister

• High fuel pressure

A higher voltage indicates that the ECU is

increasing fuel to correct for some long termlean condition. Examples of conditions whichcould cause high learned value VF:

• Atmospheric leaks into intake system

• Worn throttle shaft

• Low fuel pressure





Toyota DiagnosticCommunications Link (TDCL) The TDCL is an enhanced diagnostic checkconnector which adds a special diagnostic

TEST mode to the self diagnostic system. Itis only used on '89 and later Cressida, '92and later Camry, and all Lexus models. It islocated under the left side of the instrumentpanel.

The TDCL uses a TE2 test terminal, whichwhen grounded, triggers the special TESTmode. In TEST mode, the ECU is capable of detecting intermittent electrical faults whichare difficult to detect in a normal diagnostic

mode. The ECU eliminates most codesetting conditions when TEST mode isentered, allowing it to immediately detect amalfunction in many of the monitoredcircuits.

Using the Diagnosti cTEST Mode ProcedureWith the ignition switch off, connect terminals TE2 and E1 using SST #09842-18020 (TESTmode will not start if TE2 is grounded afterthe ignition switch is already on).

• Turn the ignition switch on; then start theengine and drive the vehicle at least 6 mphor higher (code 42, vehicle speed sensorwill set if vehicle speed does not exceed 6mph).

• Simulate driving conditions that problemoccurs under.

• When the check engine lamp comes on, jumper TE1 to El without disconnecting TE2.

• Note and record diagnostic codes (codesdisplay in same manner as in normaldiagnostic mode).

• Exit diagnostic TEST mode bydisconnecting TE2 and turning the ignitionswitch off.

Diagnostic TEST mode is also available onthe > '92 Celica 5S-FE and 3S-GTEapplications through the check connector TE2 terminal. For more information on usingthe VF terminal and the TE2 TEST modediagnostics, refer to Course #872, TCCSDiagnosis.





Position/Mode Sensors and Switches

For many components, it is important that the ECM know the position and/or mode of thecomponent. A switch is used as a sensor to indicate a position or mode. The switch may be on

the supply side or the ground side of a circuit.

Power Side Switch Circuit

A power side switch is a switch located between the power supply and load. Sometimes thepower side switch is called hot side switch because it is located on the hot side, that is, beforethe load, in a circuit. The Stop Lamp switch is a good example. When the brake pedal isdepressed, the Stop Lamp switch closes sending battery voltage to the ECM. This signals theECM that the vehicle is braking.

MODE SENSORS AND SW ITCHES




The following switches act as switches for the ECM. Usually, they are supply side switches.Note in the figure(s) their location between the battery and ECM. Many switches that commonlyuse battery voltage as the source are:

• Ignition Switch.

• Park/Neutral Switch.

• Transfer Low Position Detection Switch.

• Transfer Neutral Position Detection Switch.

• Transfer 4V;D Detection Switch.





Ground Side Switch Circuit

A ground side switch is located between the load and ground in a circuit. Inside the ECM thereis resistor (load) connected in series to the switch. The ECM measures the available voltagebetween the resistor and switch. When the switch is open, the ECM reads supply voltage. Whenthe switch is closed, voltage is nearly zero.

The following switches are typically found on the ground side of the circuit:

• TPS Idle Contact (IDL signal) The TPS Idle Contact Switch uses a 12 volt referencevoltage from the ECM.

• Power Steering Pressure Switch.

• Overdrive Switch.





Temperature Sensors The ECM needs to adjust a variety of systems based on temperatures. It is critical for properoperation of these systems that the engine reach operating temperature and the temperature isaccurately signaled to the ECM. For example, for the proper amount of fuel to be injected theECM must know the correct engine temperature. Temperature sensors measure EngineCoolant Temperature (ECT), Intake Air Temperature (IAT) and Exhaust Recirculation Gases(EGR), etc.

TEMPERATURE SENSORS




Engine Coolant Temperature (ECT) Sensor The ECT responds to change in Engine Coolant Temperature. By measuring engine coolanttemperature, the ECM knows the average temperature of the engine. The ECT is usually

located in a coolant passage just before the thermostat. The ECT is connected to the THWterminal on the ECM.

The ECT sensor is critical to many ECM functions such as fuel injection, ignition timing, variablevalve timing, transmission shifting, etc. Always check to see if the engine is at operatingtemperature and that the ECT is accurately reporting the temperature to the ECM.

Intake Air Temperature (IAT) Sensor The IAT detects the temperature of the incoming air stream. On vehicles equipped with a MAPsensor, the IAT is located in an intake air passage. On Mass Air Flow sensor equippedvehicles, the IAT is part of the MAF sensor. The IAT is connected to the THA terminal on theECM. The IAT is used for detecting ambient temperature on a cold start and intake air

temperature as the engine heats up the incoming air.

NOTE: One strategy the ECM uses to determine a cold engine start is by comparing the ECTand IAT signals. If both are within 8'C (15'F) of each other, the ECM assumes it is a cold start. This strategy is important because some diagnostic monitors, such as the EVAP monitor, arebased on a cold start.

TEMPERATURE SENSORS




Exhaust Gas Recirculation (EGR) Temperature Sensor The EGR Temperature Sensor is located in the EGR passage and measures the temperatureof the exhaust gases. The EGR Temp sensor is connected to the THG terminal on the ECM.When the EGR valve opens, temperature increases. From the increase in temperature, theECM knows the EGR valve is open and that exhaust gases are flowing.

TEMPERATURE SENSORS




ECT, IAT, & EGR Temperature Sensor Operation Though these sensors are measuring different things, they all operate in the same way. Fromthe voltage signal of the temperature sensor, the ECM knows the temperature. As the

temperature of the sensor heats up, the voltage signal decreases. The decrease in the voltagesignal is caused by the decrease in resistance. The change in resistance causes the voltagesignal to drop.

The temperature sensor is connected in series to a fixed value resistor. The ECM supplies 5volts to the circuit and measures the change in voltage between the fixed value resistor and thetemperature sensor.

When the sensor is cold, the resistance of the sensor is high, and the voltage signal is high. Asthe sensor warms up, the resistance drops and voltage signal decreases. From the voltagesignal, the ECM can determine the temperature of the coolant, intake air, or exhaust gas

temperature.

The ground wire of the temperature sensors is always at the ECU usually terminal E2. Thesesensors are classified as thermistors.

Temperature Sensor Diagnost ics Temperature sensor circuits are tested for:

• opens.• shorts.• available voltage.

• sensor resistance.

The Diagnostic Tester data list can reveal the type of problem. An open circuit (high resistance)will read the coldest temperature possible. A shorted circuit (low resistance) will read thehighest temperature possible. The diagnostic procedure purpose is to isolate and identify thetemperature sensor from the circuit and ECM.

High resistance in the temperature circuit will cause the ECM to think that the temperature iscolder than it really is. For example, as the engine warms up, ECT resistance decreases, butunwanted extra resistance in the circuit will produce a higher voltage drop signal. This will mostlikely be noticed when the engine has reached operating temperatures. Note that at the upper

end of the temperature/resistance scale, ECT resistance changes very little. Extra resistance inthe higher temperature can cause the ECM to think the engine is approximately 20'F = 30'Fcolder than actual temperature. This will cause poor engine performance, fuel economy, andpossibly engine overheating.

TEMPERATURE SENSORS




Solving Open Circuit ProblemsA jumper wire and Diagnostic Tester are used to locate the problem in an open circuit.

TEMPERATURE SENSORS




Solving Shorted Circuit ProblemsCreating an open circuit at different points in the temperature circuit will isolate the short. Thetemperature reading should go extremely low (cold) when an open is created.

TEMPERATURE SENSORS




ASSIGNMENT NAME: ___________________________

1. List the three types of temperature sensors used and explain the function of each?

2. Temperature sensors are actually ______________?

3. Draw a sample temperature sensor circuit. (Label all parts)

4. The ECT us used by the computer to control what functions?

5. What PCM strategy is used when both the IAT and ECT are within 15’F of each other?

6. Temperature sensors are tested for:

7. Describe the procedure of testing a temperature sensor.

TEMPERATURE SENSORS




Position SensorsIn many applications, the ECM needs to know the position of mechanical components. The Throttle Position Sensor (TPS) indicates position of the throttle valve. Accelerator Pedal Position(APP) sensor indicates position of the accelerator pedal. Exhaust Gas Valve (EGR) ValvePosition Sensor indicates position of the EGR Valve. The vane air flow meter uses thisprinciple.

Electrically, these sensors operate the same way. A wiper arm inside the sensor ismechanically connected to a moving part, such as a valve or vane. As the part moves, the wiperarm also moves. The wiper arm is also in contact with a resistor. As the wiper arm moves onthe resistor, the signal voltage output changes. At the point of contact the available voltage is the

signal voltage and this indicates position. The closer the wiper arm gets to VC voltage, thehigher the signal voltage output. From this voltage, the ECM is able to determine the position of a component.

POSITION SENSORS




Throttle Position Sensor The TPS is mounted on the throttle body and converts the throttle valve angle into an electricalsignal. As the throttle opens, the signal voltage increases.

The ECM uses throttle valve position information to know:

• engine mode: idle, part throttle, wide open throttle.

• switch off AC and emission controls at Wide Open Throttle (WOT).

• air-fuel ratio correction.

• power increase correction.

• fuel cut control.

The basic TPS requires three wires. Five volts are supplied to the TPS from the VC terminal of the ECM. The TPS voltage signal is supplied to the VTA terminal. A ground wire from the TPS tothe E2 terminal of the ECM completes the circuit.

At idle, voltage is approximately 0.6 - 0.9 volts on the signal wire. From this voltage, the ECM

knows the throttle plate is closed. At wide open throttle, signal voltage is approximately 3.5 - 4.7volts.

Inside the TPS is a resistor and a wiper arm. The arm is always contacting the resistor. At thepoint of contact, the available voltage is the signal voltage and this indicates throttle valveposition. At idle, the resistance between the VC (or VCC terminal and VTA terminal is high,therefore, the available voltage is approximately 0.6 - 0.9 volts. As the contact arm moves closerthe VC terminal (the 5 volt power voltage), resistance decreases and the voltage signalincreases.

POSITION SENSORS




Some TPS incorporate a Closed Throttle Position switch (also called an idle contact switch). This switch is closed when the throttle valve is closed. At this point, the ECM measures 0 voltsand there is 0 volts at the IDL terminal. When the throttle is opened, the switch opens and theECM reads +B voltage at the IDL circuit.

POSITION SENSORS




The TPS on the ETCS-i system has two contact arms and to resistors in one housing. The firstsignal line is VTA1 and the second signal line is VTA2.

VTA2 works the same, but starts at a higher voltage output and the voltage change rate isdifferent from VTA1 As the throttle opens the two voltage signals increase at a different rate. TheECM uses both signals to detect the change in throttle valve position. By having two sensors,ECM can compare the voltages and detect problems.

POSITION SENSORS




Accelerator Pedal Posit ion (APP) Sensor

The APP sensor is mounted on the throttle body of the ETCS-i. The APP sensor converts theaccelerator pedal movement and position into two electrical signals. Electrically, the APP is

identical in operation to the TPS.

EGR Valve Position Sensor The EGR Valve Position Sensor is mounted on the EGR valve and detects the height of the EGRvalve. The ECM uses this signal to control EGR valve height. The EGR Valve Position Sensorconverts the movement and position of the EGR valve into an electrical signal. Operation isidentical to the TPS except that the signal arm is moved by the EGR valve.

Position Sensor Diagnostics The following explanations are to help you with the diagnostic procedures in the Repair Manual.

The explanations below are representative to the order listed in the RM. You may find differentorders in the RM.

Diagnostic Tester

Comparing the position of the sensor to Diagnostic Tester data is a convenient way of observing sensor operation. For example, with the TPS, the lowest percentage measured withKey On/Engine Off is with the throttle valve at its minimum setting, and the highest percentagewill be at Wide Open Throttle.

POSITION SENSORS




Inspect Throttle Position Sensor

On some models, you will find TPS checks in the Throttle Body on Vehicle Inspection in the SFSection.

POSITION SENSORS




POSITION SENSORS




ASSIGNMENT NAME: ___________________________

1. What are some of the common uses of position sensors? List them.

2. Explain how a position sensor (potentiometer) works?

3. Draw a sample position sensor circuit. Label all parts.

4. The PCM (ECM) uses throttle valve position information to control what functions?

5. Why do some TPS have an IDL contact and how does the PCM use this information?

6. What are the typical voltage values of a TPS? (Reference, idle, WOT)

7. Why does the PCM use an EGR position sensor and how is it used? Explain the strategy

behind this sensor.

8. Explain the testing procedure for a position sensor such as a TPS. (In detail)

POSITION SENSORS




Mass Air Flow (MAF) Sensors The Mass Air Flow Sensors converts the amount of air drawn into the engine into a voltagesignal. The ECM needs to know intake air volume to calculate engine load. This is necessary todetermine how much fuel to inject, when to ignite the cylinder, and when to shift the

transmission. The air flow sensor is located directly in the intake air stream, between the aircleaner and throttle body where it can measure incoming air.

There are different types of Mass Air Flow sensors. The vane air flow meter and Karmen vortexare two older styles of air flow sensors and they can be identified by their shape. The newer,and more common is the Mass Air Flow (MAF) sensor.

Mass Air Flow Sensor: Hot Wire Type The primary components of the MAF sensor are a thermistor, a platinum hot wire, and anelectronic control circuit.

The thermistor measures the temperature of the incoming air. The hot wire is maintained at aconstant temperature in relation to the thermistor by the electronic control circuit. An increase in

AIR FLOW SENSORS




air flow will cause the hot wire to lose heat faster and the electronic control circuitry willcompensate by sending more current through the wire. The electronic control circuitsimultaneously measures the current flow and puts out a voltage signal (VG) in proportion to

current flow.

This type of MAF sensor also has an Intake Air Temperature (IAT) sensor as part of the housingassembly. Its operation is described in the IAT section of Temperature Sensors. When lookingat the EWD, there is a ground for the MAF sensor and a ground (E2) for the IAT sensor.

AIR FLOW SENSORS




DiagnosisDiagnosis of the MAF sensor involves visual, circuit, and component checks. The MAF sensorpassage must be free of debris to operate properly. If the passage is plugged, the engine will

usually start, but run poorly or stall and may not set a DTC.

AIR FLOW SENSORS




Vane Air Flow Meter The Vane Air Flow Meter provides the ECM with an accurate measure of the load placed on theengine. The ECM uses it to calculate basic injection duration and basic ignition advance angle.Vane Air Flow Meters consist of the following components:

• Measuring Plate.

• Compensation Plate.

• Return Spring.

• Potentiometer.

• Bypass Air Passage.

• Idle Adjusting Screw (factory adjusted).

• Fuel Pump Switch.

• Intake Air Temperature (IAT) Sensor.

AIR FLOW SENSORS




During engine operation, intake air flow reacts against the measuring plate (and return spring)and deflects the plate in proportion to the volume of air flow passing the plate. A compensationplate (which is attached to the measuring plate) is located inside a damping chamber and actsas a "shock absorber" to prevent rapid movement or vibration of the measuring plate.

Movement of the measuring plate is transferred through a shaft to a slider (movable arm) on thepotentiometer. Movement of the slider against the potentiometer resistor causes a variablevoltage signal back to the VS terminal at the ECM. Because of the relationship of the measuring

plate and potentiometer, changes in the VS signal will be proportional to the air intake volume.

AIR FLOW SENSORS




The r2 resistor (connected in parallel with r1) allows the meter to continue to provide a VSsignal in the event that an open occurs in the main potentiometer (r1). The Vane Air Flow Meteralso has a fuel pump switch built into the meter that closes to maintain fuel pump operation

once the engine has started and air flow has begun.

The meter also contains a factory adjusted idle adjusting screw that is covered by a tamper -resistant plug. The repair manual does not provide procedures on resetting this screw in caseswhere it has been tampered with.

Types of VAF Meters There were two major types of VAF meters. The first design, is the oldest type. It uses batteryvoltage for supply voltage. With this type of VAF meter, as the measuring plate opens signalvoltage increases.

AIR FLOW SENSORS




Karmen Vortex Air Flow Meter This air flow meter provides the same type of information (intake air volume) as the Vane AirFlow Meter. It consists of the following components:

• Vortex Generator.

• Mirror (metal foil).

• Photo Coupler (LED and photo transistor).

Karman Vortex Air Flow Meter Operation

Intake air flow reacting against the vortex generator creates a swirling effect to the airdownstream, very similar to the wake created in the water after a boat passes. This wake orflutter is referred to as a "Karman Vortex." The frequencies of the vortices vary in proportion tothe intake air velocity (engine load).

AIR FLOW SENSORS




The vortices are metered into a pressure directing hole from which they act upon the metal foilmirror. The air flow against the mirror causes it to oscillate in proportion to the vortex frequency. This causes the illumination from the photo coupler's LED to be alternately applied to and

diverted away from a photo transistor. As a result, the photo transistor alternately grounds oropens the 5-volt KS signal to the ECM.

This creates a 5 volt square wave signal that increases frequency in proportion to the increasein intake air flow. Because of the rapid, high frequency nature of this signal, accurate signalinspection at various engine operating ranges requires using a high quality digital multimeter(with frequency capabilities) or oscilloscope.

AIR FLOW SENSORS




ASSIGNMENT NAME: ___________________________

1. Explain the purpose of a Mass Air Flow sensor?

2. List the different types of Mass Air Flow Sensors?

3. Explain in detail the constructions and how a MAF (hot wire type) works?

4. What type of voltage signal is produced by a MAF and what would you expect tochange as RPM is increased?

5. Explain in detail the testing procedure of a MAF sensor.

6. Explain in detail the constructions and how a VAF (Vane Air Flow Meter) works?

7. What type of voltage signal is produced by a VAF and what would you expect tochange as RPM is increased?

8. Explain in detail the constructions and how a Karmen Vortex works?

9. What type of voltage signal is produced by a Karmen Vortex and what would youexpect to change as RPM is increased?

AIR FLOW SENSORS




Pressure SensorsPressure sensors are used to measure intake manifold pressure, atmospheric pressure,vapor pressure in the fuel tank, etc. Though the location is different, and the pressures beingmeasured vary, the operating principles are similar.

PRESSURE SENSORS




Manifold Absolute Pressure (MAP) Sensor

In the Manifold Absolute Pressure (MAP) sensor there is a silicon chip mounted inside areference chamber. On one side of the chip is a reference pressure. This reference pressure iseither a perfect vacuum or a calibrated pressure, depending on the application. On the otherside is the pressure to be measured. The silicon chip changes its resistance with the changesin pressure. When the silicon chip flexes with the change in pressure, the electrical resistanceof the chip changes. This change in resistance alters the voltage signal. The ECM interprets thevoltage signal as pressure and any change in the voltage signal means there was a change inpressure.

Intake manifold pressure is a directly related to engine load. The ECM needs to know intakemanifold pressure to calculate how much fuel to inject, when to ignite the cylinder, and otherfunctions. The MAP sensor is located either directly on the intake manifold or it is mounted highin the engine compartment and connected to the intake manifold with vacuum hose. It is criticalthe vacuum hose not have any kinks for proper operation.

PRESSURE SENSORS




The MAP sensor uses a perfect vacuum as a reference pressure. The difference in pressurebetween the vacuum pressure and intake manifold pressure changes the voltage signal. TheMAP sensor converts the intake manifold pressure into a voltage signal (PIM).

PRESSURE SENSORS




The MAP sensor voltage signal is highest when intake manifold pressure is highest (ignitionkey ON, engine off or when the throttle is suddenly opened). The MAP sensor voltage signal islowest when intake manifold pressure is lowest on deceleration with throttle closed.

MAP Sensor Diagnosis

The MAP sensor can cause a variety of driveability problems since it is an important sensor forfuel injection and ignition timing.

Visually check the sensor, connections, and vacuum hose. The vacuum hose should be free of kinks, leaks, obstructions and connected to the proper port.

The VC (VCQ wire needs to supply approximately 5 volts to the MAP sensor. The E2 ground wireshould not have any resistance.

Sensor calibration and performance is checked by applying different pressures and comparingto the voltage drop specification. The voltage drop is calculated by subtracting the PIM voltagefrom the VC voltage.

PRESSURE SENSORS




Barometric Pressure Sensor

The Barometric Pressure Sensor, sometimes called a High Altitude Compensator (HAC),measures the atmospheric pressure. Atmospheric pressure varies with weather and altitude.At higher elevations the air is less dense, therefore, it has less pressure. In addition, weatherchanges air pressure. This sensor operates the same as the MAP sensor except that itmeasures atmospheric pressure. It is located inside the ECM. If it is defective, the entire ECMmust be replaced.

Turbocharging Pressure Sensor

The turbocharging pressure sensor operates identically to the MAP sensor and is used tomeasure intake manifold pressure. The only difference is that when there is boost pressure,the voltage signal goes higher than on a naturally aspirated engine.

PRESSURE SENSORS




Vapor Pressure Sensor

The Vapor Pressure Sensor (VPS) measures the vapor pressure in the evaporative emissioncontrol system. The Vapor Pressure Sensor may be located on the fuel tank, near the charcoalcanister assembly, or in a remote location.

PRESSURE SENSORS




This sensor uses a silicon chip with a calibrated reference pressure on one side of the chip,the other side of the chip is exposed to vapor pressure. Changes in vapor pressure cause thechip to flex and vary the voltage signal to the ECM. The voltage signal out depends on the

difference between atmospheric pressure and vapor pressure. As vapor pressure increasesthe voltage signal increases. This sensor is sensitive to very small pressure changes(1.0 psi = 51.7 mmHg).

Vapor pressure sensors come in variety of configurations. When the VPS is mounted directly onthe fuel pump assembly, no hoses are required. For remote locations, there may be one or twohoses connected to the VPS. If the VPS uses one hose, the hose is connected to vaporpressure. In the two hose configuration, one hose is connected to vapor pressure, the otherhose to atmospheric pressure. It is important that these hoses are connected to the properport. If they are reversed, DTCs will set.

PRESSURE SENSORS




VPS DiagnosisCheck all hoses for proper connection, restrictions, and leaks. Check the VC and E2 voltages.Apply the specified pressure and read sensor voltage output. The vapor pressure sensor iscalibrated for the pressures found in the EVAP system, so apply only the specified amount toprevent damaging the sensor.

PRESSURE SENSORS




ASSIGNMENT NAME: ___________________________

1. List the different types of Pressure Sensors used on cars?

2. Explain in detail the constructions and how a MAP (Manifold Absolute Pressure)sensor works?

3. What type of voltage signal is produced by a MAP and what would you expect tochange as the engine goes from idle to W.O.T.?

4. Explain in detail the testing procedure of a MAP sensor.

5. Explain the need for a Barometric Pressure Sensor?

6. Explain the need for a Turbocharging Pressure Sensor and how does this compare

to a MAP sensor?

7. Explain the need for a EVAP Vapor Pressure Sensor and how does this compareto a MAP sensor?

PRESSURE SENSORS




Position / Speed Sensors

Position/speed sensors provide information to the ECM about the position of a component, thespeed of a component, and the change in speed of a component. The following sensors

provide this data:

• Camshaft Position Sensor (also called G sensor).

• Crankshaft Position Sensor (also called NE sensor).

• Vehicle Speed Sensor.

The Camshaft Position Sensor, Crankshaft Position Sensor, and one type of vehicle speedsensor are of the pick-up coil type sensor.

This type of sensor consists of a permanent magnet, yoke, and coil. This sensor is mountedclose to a toothed gear. As each tooth moves by the sensor, an AC voltage pulse is induced inthe coil. Each tooth produces a pulse. As the gear rotates faster there more pulses areproduced. The ECM determines the speed the component is revolving based on the number of pulses. The number of pulses in one second is the signal frequency.

POSITION / SPEED SENSORS




Pick-Up Coil (Variable Reluctance) Type Sensors The distance between the rotor and pickup coil is critical. The further apart they are, the weakerthe signal.

Not all rotors use teeth. Sometimes the rotor is notched, which will produce the same effect.

These sensors generate AC voltage, and do not need an external power supply. Anothercommon characteristic is that they have two wires to carry the AC voltage.

The wires are twisted and shielded to prevent electrical interference from disrupting the signal. The EWD will indicate if the wires are shielded.

By knowing the position of the camshaft, the ECM can determine when cylinder No. I is on thecompression stroke. The ECM uses this information for fuel injection timing, for direct ignitionsystems and for variable valve timing systems.

This sensor is located near one of the camshafts. With variable timing V-type engines, there isone sensor for each cylinder bank. On distributor ignition systems, it is often called the Gsensor and is located in the distributor.

An AC signal is generated that is directly proportional to camshaft speed. That is, as thecamshaft revolves faster the frequency increases.





Camshaft Posit ion Sensor (G Sensor) The terminal on the ECM is designated with a letter G, and on some models a G and a number,such as G22 is used.

Variable Valve Position Sensor

Some variable valve timing systems call the Camshaft Position Sensor the Variable ValvePosition Sensor. See section on variable valve timing systems for more information.





Crankshaft Position Sensor (NE Sensor)

The ECM uses crankshaft position signal to determine engine RPM, crankshaft position, andengine misfire. This signal is referred to as the NE signal. The NE signal combined with the Gsignal indicates the cylinder that is on compression and the ECM can determine from itsprogramming the engine firing order. See Section 3 on ignition systems for more information.





Vehicle Speed Sensor (VSS) The ECM uses the Vehicle Speed Sensor (VSS) signal to modify engine functions and initiatediagnostic routines. The VSS signal originates from a sensor measuring transmission/transaxle output speed or wheel speed. Different types of sensors have been used dependingon models and applications.

On some vehicles, the vehicle speed sensor signal is processed in the combination meter andthen sent to the ECM.

On some anti-lock brake system (ABS) equipped vehicles, the ABS computer processes thewheel speed sensor signals and sends a speed sensor signal to the combination meter andthen to the ECM. You will need to consult the EWD to confirm the type of system you are workingon.

Pick-Up Coil (Variable Reluctance) Type

This type of VSS operates on the variable reluctance principle discussed earlier and it is usedto measure transmission/ transaxle output speed or wheel speed depending on type of system.





Magnetic Resistance Element (MRE) Type The MIRE is driven by the output shaft on a transmission or output gear on a transaxle. Thissensor uses a magnetic ring that revolves when the output shaft is turning. The MIRE sensesthe changing magnetic field. This signal is conditioned inside the VSS to a digital wave. Thisdigital wave signal is received by the Combination meter, and then sent to the ECM. The MIRErequires an external power supply to operate.

Reed Switch Type The reed switch type is driven by the speedometer cable. The main components are a magnet,reed switch, and the speedometer cable. As the magnet revolves the reed switch contacts openand close four times per revolution. This action produces 4 pulses per revolution. From thenumber of pulses put out by the VSS, the combination meter/ECM is able to determine vehiclespeed.





ASSIGNMENT NAME: ___________________________

1. What are the “G” and “NE” sensors?

2. Explain in detail how an magnetic pick up coil type Cam or Crank sensor works.

3. Explain how the PCM (ECM) uses the Crankshaft position sensor signal.

4. Draw the scope pattern of both a Cam sensor and Crank sensor.

5. What is the function of a vehicle speed sensor (VVS) and list the three types.

6. Explain how a Pick UP Coil (Variable Reluctance) type VSS works?

7. Explain how a Magnetic Resistance Element (MRE) type VSS works?

8. Explain how a Reed Switch type VSS works?





Oxygen and Air/Fuel Ratio Sensors The ECM uses an oxygen sensor to ensure the air/fuel ratio is correct for the catalytic converter.Based on the oxygen sensor signal, the ECM will adjust the amount of fuel injected into theintake air stream.

There are different types of oxygen sensors, but two of the more common types are:

• the narrow range oxygen sensor, the oldest style, simply called the oxygen sensor.

• wide range oxygen sensor, the newest style, called the air/fuel ratio (A/F) sensor.

Also used on very limited models in the early 90s, was the Titania oxygen sensor.

OBD II vehicles require two oxygen sensors: one before and one after the catalytic converter. The oxygen sensor, or air/fuel ratio sensor, before the catalytic converter is used by the ECM toadjust the air/fuel ratio. This sensor in OBD II terms is referred to as sensor 1. On V-type

engines one sensor will be referred to as Bank I Sensor 1 and the other as Bank 2 Sensor 1. The oxygen sensor after the catalytic converter is used by the ECM primarily to determinecatalytic converter efficiency. This sensor is refer-red to as sensor 2. With two catalyticconverters, one sensor will be Bank 1 Sensor 2 and the other as Bank 2 Sensor 2.

OXYGEN / AIR FUEL SENSORS




Oxygen Sensor This style of oxygen sensor has been in service the longest time. It is made of zirconia(zirconium dioxide), platinum electrodes, and a heater. The oxygen sensor generates a voltagesignal based on the amount of oxygen in the exhaust compared to the atmospheric oxygen. Thezirconia element has one side exposed to the exhaust stream, the other side open to theatmosphere. Each side has a platinum electrode attached to Zirconium dioxide element.

The platinum electrodes conduct the voltage generated. Contamination or corrosion of theplatinum electrodes or zirconia elements will reduce the voltage signal output.





Operation

When exhaust oxygen content is high, oxygen sensor voltage output is low. When exhaustoxygen content is low, oxygen sensor voltage output is high. The greater the difference inoxygen content between the exhaust stream and atmosphere, the higher the voltage signal.

From the oxygen content, the ECM can determine if the air/fuel ratio is rich or lean and adjuststhe fuel mixture accordingly. A rich mixture consumes nearly all the oxygen, so the voltagesignal is high, in the range of 0.6 - 1.0 volts. A lean mixture has more available oxygen aftercombustion than a rich mixture, so the voltage signal is low, 0.4 - 0.1 volts. At the stoichiometricair/fuel ratio (14.7: 1), oxygen sensor voltage output is approximately 0.45 volts.





Small changes in the air/fuel ratio from the stoichiometric point radically changes the voltagesignal. This type of oxygen sensor is sometimes referred to as a narrow range sensor becauseit cannot detect the small changes in the exhaust stream oxygen content produced by changesin the air/fuel mixture. The ECM will continuously add and subtract fuel producing a rich/leancycle. Refer to Closed Loop Fuel Control in the Fuel Injection section for more information.

NOTE: Think of the oxygen sensor as a switch. Each time the air/fuel ratio is at stoichiometry(14.7: 1) the oxygen sensor switches either high or low.





The oxygen sensor will only generate an accurate signal when it has reached a minimumoperating temperature of 400'C (7500F). To quickly warm up the oxygen sensor and to keep ithot at idle and light load conditions, the oxygen sensor has a heater built into it. This heater iscontrolled by the ECM. See Oxygen Sensor Heater Control for more information.





Air/Fuel Ratio Sensor The Air/Fuel Ratio (A/F) sensor is similar to the narrow range oxygen sensor. Though it appearssimilar to the oxygen sensor, it is constructed differently and has different operatingcharacteristics.

The A/F sensor is also referred to as a wide range or wide ratio sensor because of its ability todetect air/fuel ratios over a wide range.

The advantage of using the A/F sensor is that the ECM can more accurately meter the fuelreducing emissions. To accomplish this, the A/F sensor:

• operates at approximately 650'C (1200'F), much hotter than the oxygen sensor 400'C(750'F).

• changes its current (amperage) output in relation to the amount of oxygen in the exhauststream.





OperationA detection circuit in the ECM detects the change and strength of current flow and puts out avoltage signal relatively proportional to exhaust oxygen content.

NOTE: This voltage signal can only be measured by using the Diagnostic Tester or OBD II

compatible scan tool. The A/F sensor current output cannot be accurately measured directly. If an OBD 11 scan tool is used, refer to the Repair Manual for conversion, for the output signal isdifferent.

The A/F sensor is designed so that at stoichiometry, there is no current flow and the voltage putout by the detection circuit is 3.3 volts. A rich mixture, which leaves very little oxygen in theexhaust stream, produces a negative current flow. The detection circuit will produce a voltagebelow 3.3 volts. A lean mixture, which has more oxygen in the exhaust stream, produces apositive current flow. The detection circuit will now produce a voltage signal above 3.3 volts.





NOTE The A/F sensor voltage output is the opposite of what happens in the narrow range oxygensensor. Voltage output through the detection circuit increases as the mixture gets leaner.

Also, the voltage signal is proportional to the change in the air/fuel mixture. This allows the ECMto more accurately judge the exact air/fuel ratio under a wide variety of conditions and quicklyadjust the amount of fuel to the stoichiometric point. This type of rapid correction is not possiblewith the narrow range oxygen sensor. With an A/F sensor, the ECM does not follow a rich leancycle. Refer to Closed Loop Fuel Control in the Fuel Injection chapter for more information.

HINT Think of the A/F sensor as a generator capable of changing polarity. When the fuel mixture isrich (high exhaust oxygen content), the A/F generates current in the negative (-) direction. As theair/fuel mixture gets leaner (less oxygen content), the A/F sensor generates current in the

positive (+) direction. At the stoichiometric point, no current is generated.

The detection circuit is always measuring the direction and how much current is beingproduced. The result is that the ECM knows exactly how rich or lean the mixture is and canadjust the fuel mixture much faster than the oxygen sensor based fuel control system. Therefore, there is no cycling that is normal for a narrow range oxygen sensor system. Instead,A/F sensor output is more even and usually around 3.3 volts.

Oxygen Sensor Diagnosis Service There are several factors that can affect the normal functioning of the oxygen sensor. It isimportant to isolate if it is the oxygen sensor itself or some other factor causing the oxygen

sensor to behave abnormally. See Course 874 Technician Reference book for moreinformation.

A contaminated oxygen sensor, will not produce the proper voltages and will not switchproperly. The sensor can be contaminated from engine coolant, excessive oil consumption,additives used in sealants, and the wrong additives in gasoline. When lightly contaminated, thesensor is said to be "lazy," because of the longer time it takes to switch from rich to lean and/orvice versa. This will adversely affect emissions and can produce driveability problems.

Many factors can affect the operation of the oxygen sensor, such as a vacuum leak, an EGRleak, excessive fuel pressure, etc.





It is also very important that the oxygen sensor and heater electrical circuits be in excellentcondition. Excessive resistance, opens, and shorts to ground will produce false voltagesignals.

In many cases, DTCs or basic checks will help locate the problem.

Oxygen Sensor Heater For the oxygen sensor to deliver accurate voltage signals quickly, the sensor needs to beheated. A PTC element inside the oxygen sensor heats up as current passes through it. TheECM turns on the circuit based on engine coolant temperature and engine load (determinedfrom the MAF or MAP sensor signal). This heater circuit uses approximately 2 amperes.

The heater element resistance can be checked with a DVOM. The higher the temperature of theheater, the greater the resistance.

The oxygen sensor heater circuit is monitored by the ECM for proper operation. If a malfunctionis detected, the circuit is turned off. When this happens, the oxygen sensor will produce little orno voltage, and possible set DTC P0125.





Air/Fuel Ratio Sensor Heater This heater serves the same purpose as the oxygen sensor heater, but there are some veryimportant differences.

Engines using two A/F sensors use a relay, called the A/F Relay, which is turned onsimultaneously with the EFI Relay. This heater circuit carries up to 8 amperes (versus 2amperes for 0, heater) to provide the additional heat needed by the A/F sensor.

This heater circuit is duty ratio controlled pulse width modulator (PMW) circuit. When cold, theduty ratio is high. The circuit is monitored for proper operation. If a malfunction is detected in thecircuit, the heater is turned off. When this happens, the A/F sensor will not operate under mostconditions and DTC P0125 will set.

Air/Fuel Ratio Sensor Heater Diagnosis

Diagnosis of the heater is a similar to the oxygen sensor. Since the A/F sensor requires moreheat, the heater is on for longer periods of time and is usually on under normal drivingconditions.

Because the heater circuit carries more current, it is critical that all connections fit properly andhave no resistance.

The relay is checked in the same manner as other relays.

Titania Element Type Oxygen Sensor This oxygen sensor consists of a semiconductor element made of titanium dioxide (TiO2,which is, like ZrO2, a kind of ceramic). This sensor uses a thick film type titania element formedon the front end of a laminated substrate to detect the oxygen concentration in the exhaust gas.





Operation The properties of titania are such that its resistance changes in accordance with the oxygenconcentration of the exhaust gas. This resistance changes abruptly at the boundary between alean and a rich theoretical air/fuel ratio, as shown in the graph. The resistance of titania alsochanges greatly in response to changes in temperature. A heater is, thus built into thelaminated substrate to keep the temperature of the element constant.





This sensor is connected to the ECM as shown in the following circuit diagram. A 1.0 voltpotential is supplied at all times to the 0" positive (+) terminal by the ECM. The ECM has a built-in comparator that compares the voltage drop at the Ox terminal (due to the change in

resistance of the titania) to a reference voltage (0.45 volts). If the result shows that the Oxvoltage is greater than 0.45 volts (that is, if the oxygen sensor resistance is low), the ECM judges that the air/fuel ratio is rich. If the 0, voltage is lower than 0.45 volts (oxygen sensorresistance high), it judges that the air/fuel ratio is lean.





ASSIGNMENT NAME: ___________________________

1. What is the purpose and function of an Oxygen Sensor?

2. Explain in detail the operation of the Zirconium Oxygen Sensor

3. Explain in detail how the PCM (ECM) uses the O2 sensor information.

4. Draw an scope pattern of a properly functioning O2 sensor.

5. Explain in detail the test procedure for an zirconium O2 Sensor.

6. Explain in detail the operation of the Air Fuel Ration Sensor.





7. Explain in detail the test procedure for an Air Fuel Ration Sensor.

8. Explain how the heater circuit is controlled in an Air Fuel Ratio Sensor

9. Explain in detail the operation of the Titania Oxygen Sensor.





Knock Sensor

The Knock Sensor detects engine knock and sends a voltage signal to the ECM. The ECM usesthe Knock Sensor signal to control timing.

Engine knock occurs within a specific frequency range. The Knock Sensor, located in theengine block, cylinder head, or intake manifold is tuned to detect that frequency.

Inside the knock sensor is a piezoelectric element. Piezoelectric elements generate a voltagewhen pressure or a vibration is applied to them. The piezoelectric element in the knock sensoris tuned to the engine knock frequency.

KNOCK SENSORS




The vibrations from engine knocking vibrate the piezoelectric element generating a voltage. Thevoltage output from the Knock Sensor is highest at this time.

KNOCK SENSORS




ASSIGNMENT NAME: ___________________________

1. What is the purpose or function of a Knock Sensor?

2. Explain how the PCM (ECM) uses the Knock sensor input signal?

3. Where are Knock sensors usually located?

4. Explain the construction of a Knock Sensor?

5. Draw a scope pattern of a Knock Sensor?

KNOCK SENSORS




Ignition System Overview The purpose of the ignition system is to ignite the air/fuel mixture in the combustion chamber atthe proper time. In order to maximize engine output efficiency, the air-fuel mixture must be

ignited so that maximum combustion pressure occurs at about 10' after top dead center (TDC).

However, the time from ignition of the air-fuel mixture to the development of maximumcombustion pressure varies depending on the engine speed and the manifold pressure;ignition must occur earlier when the engine speed is higher and later when it is lower.

IGNITION #1 - IGNITION OVERVIEW




In early systems, the timing is advanced and retarded by a governor advancer in the distributor.

Furthermore, ignition must also be advanced when the manifold pressure is low (i.e. whenthere is a strong vacuum). However, optimal ignition timing is also affected by a number of other factors besides engine speed and intake air volume, such as the shape of thecombustion chamber, the temperature inside the combustion chamber, etc. For these reasons,electronic control provides the ideal ignition timing for the engine.





Electronic Spark Advance OverviewIn the Electronic Spark Advance (ESA) system, the engine is provided with nearly ideal ignitiontiming characteristics. The ECM determines ignition timing based sensor inputs and on itsinternal memory, which contains the optimal ignition timing data for each engine runningcondition. After determining the ignition timing, the ECM sends the ignition Timing signal (IGT)to the igniter. When the IGT signal goes off, the Igniter will turn on shut off primary current flow inthe ignition coil producing a high voltage spark (7kV - 35kV) in the cylinder.

Since the ESA always ensures optimal ignition timing, emissions are lowered and both fuel

efficiency and engine power output are maintained at optimal levels.

Types of Ignit ion SystemsIgnition systems are divided into three basic categories:

• Distributor.

• Distributorless Ignition System (DLI) Electronic Ignition.

• Direct Ignition System (DIS).





Essential Ignition System ComponentsRegardless of type the essential components are:

• Crankshaft sensor (Ne signal).

• Camshaft sensor (also called Variable Valve Timing sensor) (G signal).

• Igniter.

• Ignition coil(s), harness, spark plugs.

• ECM and inputs.

Ignition Spark Generation The ignition coil must generate enough power to produce the spark needed to ignite the air/fuelmixture. To produce this power, a strong magnetic field is needed. This magnetic field iscreated by the current flowing in the primary coil. The primary coil has a very low resistance(approximately 1-4 ohms) allowing current flow. The more current, the stronger the magneticfield. The power transistor in the igniter handles the high current needed by the primary coil.

Another requirement to produce high voltages is that the current flow in the primary coil must beturned off quickly. When the transistor in the igniter turns off, current flow momentarily stops andthe magnetic field collapses. As the rapidly collapsing magnetic field passes through thesecondary winding, voltage (electrical pressure) is created. If sufficient voltage is created toovercome the resistance in the secondary circuit, there will be current flow and a sparkgenerated.





NOTE: The higher the resistance in the secondary circuit, the more voltage that will be neededto get the current to flow and the shorter spark duration. This is important when observing theignition spark pattern.

IGT Signal The primary coil current flow is controlled by the ECM through the Ignition Timing (IGT) signal. The IGT signal is a voltage signal that turns on/off the main transistor in the igniter. When IGTsignal voltage drops to 0 volts, the transistor in the igniter turns off. When the current in theprimary coil is turned off, the rapidly collapsing magnetic field induces a high voltage in thesecondary coil. If the voltage is high enough to overcome the resistance in the secondary circuit,there will be a spark at the spark plug.

IGCOn some ignition systems, the circuit that carries the primary coil current is called IGC. lGC isturned on and off by the igniter based on the IGT signal.





Igniter The primary function of the igniter is to turn on and off the primary coil current based on the IGTsignal received from the ECM. The igniter or ECM may perform the following functions:

• Ignition Confirmation (IGF) signal generation unit.

• Dwell angle control.

• Lock prevention circuit.

• Over voltage prevention circuit.

• Current limiting control.

• Tachometer signal.

It is critical that the proper igniter is used when replacing an igniter. The igniters are matched to

the type of ignition coil and ECM.

IGF Signal The IGF signal is used by the ECM to determine if the ignition system is working. Based on IGF,the ECM will keep power supplied to the fuel pump and injectors on most ignition systems.Without IGF, the vehicle will start momentarily, then stall. However, with some Direct IgnitionSystems with the igniter in the coil, the engine will run.





IGF Signal Detection using CEMF There are two basic methods of detecting IGF. Early systems used the Counter ElectromotiveForce (CEMF) created in the primary coil and circuit for generating the IGF signal. Thecollapsing magnetic field produces a CEMF in the primary coil. When CEMF is detected by theigniter, the igniter sends a signal to the ECM. This method is no longer used.

IGF Detection Using Primary Current Method The primary current level method measures the current level in the primary circuit. Theminimum and maximum current levels are used to turn the IGF signal on and off. The levels willvary with different ignition systems. Regardless of method, the Repair Manual shows the scope





pattern or provides you with the necessary voltage reading to confirm that the igniter isproducing the IGF signal.

Lack of an IGF on many ignition systems will produce a DTC. On some ignition systems, theECM is able to identify which coil did not produce an IGF signal and this can be accomplishedby two methods.

The first method uses an IGF line for each coil.

With the second method, the IGF signal is carried back to the ECM on a common line with theother coil(s). The ECM is able to distinguish which coil is not operating based on when the IGFsignal is received. Since the ECM knows when each cylinder needs to be ignited, it knows fromwhich coil to expect the IGF signal.





Dwell Angle Control This circuit controls the length of time the power transistor (current flow through the primarycircuit) is turned on.

The length of time during which current flows through the primary coil generally decreases asthe engine speed rises, so the induced voltage in the secondary coil decreases.

Dwell angle control refers to electronic control of the length of time during which primary currentflows through the ignition coil (that is, the dwell angle) in accordance with distributor shaftrotational speed.

Lock Prevention CircuitAt low speeds, the dwell angle is reduced to prevent excessive primary current flow, andincreased as the rotational speed increases to prevent the primary current from decreasing.

This circuit forces the power transistor to turn off if it locks up (if current flows continuously for aperiod longer than specified), to protect the ignition coil and the power transistor.

Over Voltage Prevention Circuit This circuit shuts off the power transistor(s) if the power supply voltage becomes too high, toprotect the ignition coil and the power transistor.





Current Limiting (Over Current Prevention)Current limiting control is a system that improves the rise of the flow of current in the primarycoil, ensuring that a constant primary current is flowing at all times, from the low speed to thehigh speed range, and thus making it possible to obtain a high secondary voltage.

The coil's primary resistance is reduced improving the current rise performance, and this willincrease the current flow. But without the current limiting circuit, the coil or the power transistorwill burn out. For this reason, after the primary current has reached a fixed value, it is controlledelectronically by the igniter so that a larger current will not flow.

Since the current-limiting control limits the maximum primary current, no external resistor isneeded for the ignition coil.

NOTE: Since igniters are manufactured to match ignition coil characteristics, the function andconstruction of each type are different. For this reason, if any igniter and coil other than thosespecified are combined, the igniter or coil may be damaged. Therefore, always use the correct

parts specified for the vehicle.

Tachometer SignalOn some systems the Tach signal is generated in the igniter.





NE Signal and G Signal Though there are different types of ignition systems, the use of the NE and G signals isconsistent. The NE signal indicates crankshaft position and engine RPM.

The G signal (also called VVT signal) provides cylinder identification. By comparing the G signalto the NE signal, the ECM is able to identify the cylinder on compression. This is necessary tocalculate crankshaft angle (initial ignition timing angle), identify which coil to trigger on DirectIgnition System (independent ignition), and which injector to energize on sequential fuelinjection systems.

As ignition systems and engines evolved, there have been modifications to the NE and Gsignal. Timing rotors have different numbers of teeth. For some G signal sensors, a notch isused instead of a tooth to generate a signal. Regardless, you can determine what style is usedby visually examining the timing rotor or consulting the Repair Manual. Many of the different

styles are represented with their respective ignition system.





ASSIGNMENT NAME: ___________________________

1. What is Electronic Spark Advance?

2. List the three types of ignition systems:

3. List the five essential ignition system components:

4. Explain the detail the function of the igniter:

5. Explain in detail the function and purpose of both the IGT, IGF, and IGC signals:

6. Define the term Dwell Angle Control”:

7. Explain in detail the function and purpose of both the NE and G signals:





NE Signal and G Signal Though there are different types of ignition systems, the use of the NE and G signals isconsistent. The NE signal indicates crankshaft position and engine RPM.

The G signal (also called VVT signal) provides cylinder identification. By comparing the G signalto the NE signal, the ECM is able to identify the cylinder on compression. This is necessary tocalculate crankshaft angle (initial ignition timing angle), identify which coil to trigger on DirectIgnition System (independent ignition), and which injector to energize on sequential fuelinjection systems.

As ignition systems and engines evolved, there have been modifications to the NE and Gsignal. Timing rotors have different numbers of teeth. For some G signal sensors, a notch isused instead of a tooth to generate a signal. Regardless, you can determine what style is usedby visually examining the timing rotor or consulting the Repair Manual. Many of the different

styles are represented with their respective ignition system.

Electronic Spark Advance OperationFor maximum engine output efficiency, the air/fuel mixture must be ignited so that maximumcombustion pressure occurs approximately 10’-15' after TDC. As engine RPM increases, thereis less time for the mixture to complete its combustion at the proper time because the piston istraveling faster. The ECM controls when the spark occurs through the IGT signal. By varying thetime the IGT signal is turned off, the ECM changes ignition spark timing.

IGNITION #2 - ELECTRONIC SPARK ADVANCE




Starting Ignition ControlIgnition timing control consists of two basic elements:

• ignition control during starting.

• after start ignition control.

Ignition Control During StartingIgnition control during starting is defined as the period when the engine is cranking and

immediately following cranking. The ignition occurs at a fixed crankshaft angle, approximately5'- 10' BTDC, regardless of engine operating conditions and this is called the initial timingangle.

Since engine speed is still below a specified RPM and unstable during and immediately afterstarting, the ignition timing is fixed until engine operation is stabilized.

The ECM recognizes the engine is being cranked when it receives the NE and G signal. Onsome models, the starter (STA) signal is also used to inform the engine is being cranked.





After-Start Ignit ion ControlAfter-start ignition control will calculate and adjust ignition timing based on engine operatingconditions. The calculation and adjustment of ignition timing is performed in a series of steps,beginning with basic ignition advance control.

Various corrections are added to the initial ignition timing angle and the basic ignition advanceangle during normal operation.

After-start ignition control is carried out during normal operation.





The various corrections (that are based on signals from the relevant sensors) are added to theinitial ignition timing angle and to the basic ignition advance angle (determined by the intake airvolume signal or intake manifold pressure signal) and by the engine speed signal:

Ignition timing = initial ignition timing angle

• basic ignition advance angle

• corrective ignition advance angle

During normal operation of after-start ignition control, the Ignition Timing (IGT) signal calculatedby the microprocessor in the ECM and is output through the back-up IC.

Basic Ignition Advance Control The ECM selects the basic ignition advance angle from memory based on engine speed, load,throttle valve position, and engine coolant temperature.

Relevant Signals:

• Intake air volume (VS, KS, or VG) (Intake manifold pressure (PIM)).• Engine speed (NE).

• Throttle position (IDL).

• Engine Coolant Temperature (THW).





Corrective Ignition Advance Control The Corrective Ignition Advance Control makes the final adjustment to the actual ignition timing. The following corrective factors are not found on all vehicles.

Warm-Up Correction The ignition timing is advanced to improve driveability when the coolant temperature is low. Insome engine models, this correction changes the advance angle in accordance with the intakeair volume (intake manifold pressure) and can advance approximately 15' (varies with enginemodel) by this correction during extremely cold weather.





Over Temperature Correction To prevent knocking and overheating, the ignition timing is retarded when the coolanttemperature is extremely high. The timing may be retarded approximately 5' by this correction.

Relevant Signals:

• ECT - THW.

• The following may also be used on some engine models.

•MAF (VS, KS, or VG).

• Engine Speed - NE signal.

• Throttle position TA or (IDL).

Stable Idling CorrectionWhen the engine speed during idling has fluctuated from the target idle speed, the ECMadjusts the ignition timing to stabilize the engine speed. The ECM is constantly calculating theaverage engine speed. If the engine speed falls below the target speed, the ECM advances the

ignition timing by a predetermined angle. If the engine speed rises above the target speed, theECM retards the ignition timing by a predetermined angle.

This correction is not executed when the engine exceeds a predetermined speed.

In some engine models, the advance angle changes depending on whether the air conditioneris on or off. In other engine models, this correction only operates when the engine speed isbelow the target engine speed.





Relevant Signals:

• Engine Speed (NE)

• TPS (VTA or IDL)

• Vehicle Speed (SPD)

EGR CorrectionWhen EGR is operating, the ignition timing is advanced according to intake air volume andengine RPM to improve driveability. EGR has the effect of reducing engine knocking, thereforethe timing can be advanced.

Relevant Signals:

• Engine Speed (NE)• TPS (VTA or IDL or PSW

• Intake air volume (VS, KS, or VG) (Intake manifold pressure (PIM))

Torque Control Correction This correction reduces shift shock and the result is that the driver feels smoother shifts. Withan electronically-controlled transaxle, each clutch and brake in the planetary gear unit of thetransmission or transaxle generates shock to some extent during shifting. in some models,this shock is minimized by delaying the ignition timing when gears are upshifted. When gearshifting starts, the ECM retards the engine ignition timing to reduce the engine torque. As a

result, the shock of engagement and strain on the clutches and brakes of the planetary gearunit is reduced and the gear shift change is performed smoothly. The ignition timing angle isretarded a maximum of approximately 200 by this correction. This correction is not performedwhen the coolant temperature or battery voltage is below a predetermined level.

Relevant Signals:

• Engine Speed (NE)

• TPS (VTA or IDL or PSW

• ECT (THW)

• Battery voltage (+B)





Knock CorrectionEngine knock, if severe enough, can cause engine damage. Combustion chamber design,gasoline octane, air/fuel ratio, and ignition timing all affect when knock will occur. Under mostengine conditions, ignition timing needs to be near the point when knock occurs to achieve thebest fuel economy, engine power output, and lowest exhaust emissions. However, the pointwhen knock occurs will vary from a variety of factors. For example, if the gasoline octane is toolow, and ignition takes place at the optimum point, knock will occur. To prevent this, a knockcorrection function is used.





When engine knocking occurs, the knock sensor converts the vibration from the knocking into avoltage signal that is detected by the ECM. According to its programming, the ECM retards thetiming in fixed steps until the knock disappears. When the knocking stops, the ECM stopsretarding the ignition timing and begins to advance the timing in fixed steps. If the ignition timingcontinues to advance and knocking occurs, ignition timing is again retarded.





The ECM is able to determine which cylinder is knocking by when the knock signal is received. The ECM knows the cylinder that is in the power stroke mode based on the NE and G signals. This allows the ECM to filter any false signals.

Some mechanical problems can duplicate engine knocking. An excessively worn connectingrod bearing or a large cylinder ridge will produce a vibration at the same frequency as engineknocking. The ECM in turn will retard the timing.

Air/Fuel Ratio Correction The engine is especially sensitive to changes in the air - fuel ratio when it is idling, so stableidling is ensured by advancing the ignition timing at this time in order to match the fuel injectionvolume of air - fuel ratio feedback correction.

This correction is not executed while the vehicle is being driven.

Relevant Signals:

• Oxygen or A/F sensor.

• TPS (VTA or IDL).

• Vehicle Speed (SPD).

Other CorrectionsEngines have been developed with the following corrections added to the ESA system (inaddition to the various corrections explained so far), in order to adjust the ignition timing with

extremely fine precision.

Transition Correction - During the transition (change) from deceleration to acceleration, theignition timing is either advanced or retarded temporarily in accordance with the acceleration.

Cruise Control Correction - When driving downhill under cruise control, in order to providesmooth cruise control operation and minimize changes in engine torque caused by fuel cut-off because of engine braking, a signal is sent from the Cruise Control ECU to the ECM to retardthe ignition timing.

Traction Control Correction - This retards the ignition timing, thus lowering the torque output by

the engine, when the coolant temperature is above a predetermined temperature and thetraction control system is operating.





Acoustic Control Induction System (ACIS) Correct ion - When the engine speed rises above apredetermined level, the ACIS operates. At that time, the ECM advances the ignition timingsimultaneously, thus improving output.

Maximum and Minimum Ignition Advance ControlIf the actual ignition timing (basic ignition advance angle + corrective ignition advance or retardangle) becomes abnormal, the engine will be adversely affected. To prevent this, the ECMcontrols the actual advance so that the sum of the basic ignition and corrective angle cannot begreater or less than preprogrammed minimum or maximum values.

Approximately, these values are:

• MAX. ADVANCE ANGLE: 35'-45'.

• MIN. ADVANCE ANGLE: 100-00.

Advance angle = Basic ignition advance angle + Corrective ignition advance angle





ASSIGNMENT NAME: ___________________________

1. Explain in detail the Electronic Spark Advance Operation:

2. Describe the three Ignition Advance Angles:

3. List the four Relevant Signals of the Basic Ignition Advance Control:

4. Explain “Warm-Up correction:

5. Explain “Over Temperature” correction and list the relevant input signals used:

6. Explain “EGR” correction and list the relevant input signals used:

7. Explain “Stable Idling” correction and list the relevant input signals used:

8. Explain “Knock” correction and list the relevant input signals used:

9. Explain in detail how the PCM (Engine Computer) uses the Knock Sensor to control timing.

10. Explain “Cruise Control” correction:





Distributor Ignition (DI) Systems The NE signal is generated by the Crankshaft Position Sensor (also called engine speed

sensor). The G signal is generated by the Camshaft Position sensor that may be located in thedistributor or on the engine.

IGNITION #3 - DISTRIBUTOR AND DISTRIBUTORLESS TYPES




At the appropriate time during cylinder compression, the ECM sends a signal called IGT to theigniter. This will turn on the transistor in the igniter sending current through the primary windingof the ignition coil. At the optimum time for ignition to occur, the ECM will turn off IGT and thetransistor will turn off current flow through the primary winding. The induced current will travelthrough the coil wire, to the distributor cap, rotor, to the distributor terminal the rotor is pointingat, high tension wire, spark plug, and ground. The rotor position determines the cylinder thatreceives the spark.





Firing Order The firing order can be found in the New Car Features book. The cylinders are identified as

follows:

• V-8 engine cylinders are numbered with odd numbered cylinders on the left bank and evennumbered cylinders on the right bank.

• V-6 engine cylinders are numbered with even on left bank and odd numbered cylinders onthe right bank.

• In-line 6 engines are numbered consecutively 1-6, with the number I cylinder at the front.

• Four cylinder engines are numbered consecutively from front to back.

Many times, original equipment distributor caps have the firing order molded into the cap.





Distributorless & Direct Ignition Systems OverviewEssentially, a Distributorless Ignition System is an ignition system without a distributor.Eliminating the distributor improved reliability by reducing the number of mechanical

components. Other advantages are:

• Greater control over ignition spark generation - There is more time for the coil to build asufficient magnetic field necessary to produce a spark that will ignite the air/fuel mixture. This reduces the number of cylinder misfires.

• Electrical interference from the distributor is eliminated - Ignition coils can be placed onor near the spark plugs. This helps eliminate electrical interference and improvereliability.

• Ignition timing can be controlled over a wider range - In a distributor, if too much advance

is applied the secondary voltage would be directed to the wrong cylinder.

All of the above reduces the chances of cylinder misfires and consequently, exhaust emissions.

Distributorless Ignition systems are usually defined as having one ignition coil with two sparkplug wires for two cylinders. Distributorless Ignition Systems use a method calledsimultaneous ignition (also called waste spark) where an ignition spark is generated from oneignition coil for two cylinders simultaneously.





Direct Ignition Systems (DIS) have the ignition coil mounted on the spark plug. DIS can come intwo forms:

• Independent ignition - one coil per cylinder.

• Simultaneous ignition - one coil for two cylinders. In this system an ignition coil ismounted directly to one spark plug and a high tension cord is connected to the otherspark plug. A spark is generated in both cylinders simultaneously.





Distributorless (Simultaneous Ignition) OperationDistributorless Ignition Systems and Direct Ignition Systems that use one coil for two cylindersuse a method known as simultaneous ignition. With simultaneous ignition systems, twocylinders are paired according to piston position. This has the effect simplifying ignition timingand reducing the secondary voltage requirement.





For example, on a V-6 engine, on cylinders one and four, the pistons occupy the same cylinderposition (both are at TDC and BDC at the same time), and move in unison, but they are ondifferent strokes. When cylinder one is on the compression stroke, cylinder four is on the

exhaust stroke, and vice versa on the next revolution.

The high voltage generated in the secondary winding is applied directly to each spark plug. Inone of the spark plugs, the spark passes from the center electrode to the side electrode, and atthe other spark plug the spark is from the side to the center electrode.





Typically, the spark plugs with this style of ignition system are platinum tipped for stable ignitioncharacteristics.

The voltage necessary for a spark discharge to occur is determined by the spark plug gap andcompression pressure. If the spark plug gap between both cylinders is equal, then a voltageproportional to the cylinder pressure is required for discharge. The high voltage generated isdivided according to the relative pressure of the cylinders. The cylinder on compression willrequire and use more of the voltage discharge than the cylinder on exhaust. This is becausethe cylinder on the exhaust stroke is nearly at atmospheric pressure, so the voltagerequirement is much lower.

When compared to a distributor ignition system, the total voltage requirement for distributorlessignition is practically the same. The voltage loss from the spark gap between the distributorrotor and cap terminal, is replaced by the voltage loss in the cylinder on the exhaust stroke inthe Distributorless Ignition System.





Direct Ignition System (DIS)As DIS has evolved, there have been changes to the function and location of the igniter. Withindependent ignition DIS, there may be one igniter for all cylinders or one igniter per cylinder.

On simultaneous ignition DIS there is one igniter for all coils. The following gives an overview of the different types used on various engines.

1 MZ-FE 94 DIS This DIS uses one igniter for all coils. The IGF signal goes low when IGT is turned on. The coilsin this system use a high voltage diode for rapid cutoff of secondary ignition. If a coil issuspected of being faulty, swap with another coil.





1 MZ-FE with DIS Simultaneous Ignition This system uses three IGT signals to trigger the ignition coils in the proper sequence. When acoil is turned on, IGF goes low.





DIS with Independent Ignition The DIS with independent ignition has the igniter built into the coil. Typically, there are four wires

that make up the primary side of the coil:

• +13.

• IGT signal.

• IGF signal.

• Ground.

The ECM is able to distinguish which coil is not operating based on when the IGF signal isreceived. Since the ECM knows when each cylinder needs to be ignited, it knows from whichcoil to expect the IGF signal.

The major advantages of DIS with independent ignition are greater reliability and less chance of cylinder misfire.





Ignition Advance Service Though the Diagnostic Tester shows the computed ignition, advance, using a timing lightconfirms that advance took place and the timing marks are in the correct position.

With Distributor Ignition Systems, the point at which ignition occurs may vary because the basereference point can be moved. It is critical that the base reference point be set to factoryspecifications.

With DLI and DIS, the base reference point is determined by the Crankshaft Position Sensorand rotor, which is non-adjustable.

The angle to which the ignition timing is set during ignition timing adjustment is called the"standard ignition timing." It consists of the initial ignition timing, plus a fixed ignition advanceangle (a value that is stored in the ECM and output during timing adjustment regardless of thecorrections, etc., that are used during normal vehicle operation).





Ignition timing adjustment is initiated by connecting terminal T1 (or TE 1) of the check connectoror TDCL with terminal E1, with the idle contacts on. This will cause the standard ignition timingsignal to be output from the back-up IC in the same way as during after-start ignition control.

The standard ignition timing angle differs depending on the engine model. When tuning up theengine, refer to the repair manual for the relevant engine.

NOTE: Even if terminal T1 or TE1 and terminal E1 are connected, the ignition timing will not befixed at the standard ignition timing unless the idle contacts are on.

Where the G and NE signal generators are in a fixed position (distributorless or direct ignitionsystems), ignition timing cannot be adjusted.

DiagnosticsWhen the igniter is built into the ignition coil, it is not possible to do a resistance check of theprimary coil winding. A bad primary winding will have to be determined by checking otherfunctions of the coil and the ignition circuit.





DTC 1300 series will set, depending on the engine and type of ignition system, when the ECMdoes NOT receive the IGF signal. IGF confirms the primary circuit of the ignition system isworking. Lack of IGF signal indicates a malfunction in the primary circuit or IGF signal related

components.

If the DTC 1300 is set based on IGF, visually check the ignition system and then check forspark. If spark is present, the engine will start then stall when the ECM does not detect IGF(EXCEPT on some engines equipped with DIS with integrated igniter). In addition, when sparkis present this confirms the secondary and primary circuits are good. The problem is mostlikely with the IGF circuitry.





ASSIGNMENT NAME: ___________________________

1. Explain in the difference between Independent (Direct) and Simultaneous (Waste Spark)Ignition systems: (include the number of coils used in each)

2. Explain in detail Simultaneous (Waste Spark) Ignition system operation:

3. Draw a basic 4 cylinder Simultaneous (Waste Spark) Ignition circuit below:

4. Explain in detail Independent (Direct) Ignition system operation:

5. Draw a basic 4 cylinder Independant (Direct) Ignition circuit below:





Fuel Injection System The purpose of the fuel injection system is to precisely inject a metered amount of fuel at thecorrect time. Based on the input sensor signals, the ECMs programming will decide when to

turn each injector on and off.

Fuel Delivery System The purpose of the fuel delivery system is to quietly deliver the proper volume of fuel at thecorrect pressure. The fuel delivery system must also meet emission and safety regulations.Major components are:

• Fuel Pump.

• Fuel Pump ECU.

• Pressure Regulator.

• Fuel Pressure Control Circuit.

• Fuel Lines.

• Fuel Tank.

• Fuel Filter.

• Pulsation Damper.

• Fuel Injectors.

• Inertia Switch.

FUEL SYSTEMS #1 - OVERVIEW




Return Fuel Delivery SystemWhen the fuel pump is activated by the ECM, pressurized fuel flows out of the tan, through thefuel filter to the fuel rail and up to the pressure regulator. The pressure regulator maintains fuel

pressure in the rail at a specified value. Fuel in excess of that consumed by engine operation isreturned to the tank by a fuel return line. A pulsation damper, mounted on the fuel rail, is usedon many engines to dampen pressure variations in the fuel rail. The injectors, when turned onby the ECM deliver fuel into the intake manifold. When the fuel pump is turned off by the ECM, acheck valve in the fuel pump closes maintaining a residual pressure in the fuel system.

Returnless Fuel Delivery System When the fuel pump is activated by the ECM pressurized fuel flows from the pump to thepressure regulator. At the pressure regulator excess fuel is directed to the bottom of the fueltank and pressurized fuel is sent out of the fuel tank, through the fuel filter, pulsation damper,and into the fuel rail. When the ECM turns on the injectors fuel is delivered into the intakemanifold.

Fuel pressure in this system is maintained at a constant and higher pressure, 44-50 psi (301-347 kPa) than the return fuel system. ECM programming and a higher fuel pressure eliminatesthe need for a vacuum modulated pressure regulator.





The returnless fuel delivery system was adopted because it lowers evaporative emissionssince no heated fuel is returned to the fuel tank. On the return fuel delivery system, fuel heatedby the engine returns to the fuel tank and has warmer fuel creating more fuel vapors.

Fuel Pump

The fuel pump is mounted in the tank and immersed in fuel. The fuel cools and lubricates thepump. When current flows through the motor, the armature and impeller rotate. The impellerdraws fuel in through a filter and discharges pressurized fuel through the outlet port. The fuelpump's pumping capacity is designed to exceed engine requirements. This insures that therewill always be enough fuel to meet engine demands.

An outlet check valve, located in the discharge outlet, maintains a residual fuel pressure in thefuel system when the engine is off. This improves starting characteristics and reduces vapor-lock. Without residual fuel pressure, the system would have to be pressurized each time theengine was started and this would increase engine starting (cranking) time. When a hot engineis shut off, fuel temperature in the lines around the engine increases. Keeping the system

pressurized increases the boiling point of the fuel and prevents the fuel from vaporizing.

A pressure relief valve will open if the fuel system becomes restricted. This is a safety device toprevent the fuel lines from rupturing and damage to the pump.





On many models the fuel pump is part of the fuel pump assembly. This assembly contains thefilters, pressure (fuel system only), sending unit, and fuel pump. Many of the components canbe serviced separately.





Jet Pump The jet pump is an additional pump used when the fuel tank bottom is divided into twochambers. Excess fuel flowing through the fuel return passes through a venturi. This creates alow pressure area around the venturi, and this action will draw the fuel out of Chamber B, andsends it into Chamber A.





Fuel Pump ControlsA variety of fuel pump control circuits and controls have been used over the years. The followingbasic methods are:

• ON/OFF Control by ECM.

• ON/OFF Control by Fuel Pump Switch.• ON/OFF Two Speed Control with a Resistor.

• ON/OFF Two Speed Control with Fuel Pump ECU.

• ON/OFF Three Speed Control with Fuel Pump ECU.

The most accurate way of determining the type of fuel control circuit is to look up the circuit inthe appropriate EVVD.





The following describes the basic methods of fuel pump control. An essential point toremember is that the fuel pump operates only when the engine is cranking or running.

ON/OFF Control by ECM The following is an explanation of how the fuel pump circuit is activated.

Engine StartWhen the engine is cranking, current flows from the IG terminal of the ignition switch to the L1coil of the EFI main relay, turning the relay on. At the same time, current flows from the STterminal of the ignition switch to the L3 coil of the circuit opening relay, turning it on to operatethe fuel pump. The fuel pump is now supplying fuel to the fuel injection system.

Note: The circuit opening relay in this example is ground side switched.

Engine RunningOnce the engine starts and the ignition key is moved to the ON (IG) position, current to the L3coil is shut off, but the ECM will keep the fuel pump on through coil L2 as long as the ECMreceives an NE signal. If the NE signal is lost at any time after starting, the ECM turns the fuelpump off.





Engine StoppedWhen the engine stops, the NE signal to the ECM stops. This turns off the transistor, therebycutting off the flow of current to the L2 coil of the circuit opening relay. As a result, the circuit

opening relay opens turning off the fuel pump.

Note: The resistor R and the capacitor C in the circuit-opening relay are for the purpose of preventing the relay contacts from opening when current stops flowing in coil L2 due toelectrical noise (fuel pumps controlled by the ECM) or to sudden drops in the intake air volume(fuel pumps controlled by fuel pump switch). They also serve to prevent sparks from beinggenerated at the relay contacts. On some models, an L3 coil is not provided in the circuit-opening relay.

ON/OFF Contro l by Fuel Pump Switch The fuel pump switch is found on older vehicles using a Vane Air Flow Meter. The air moves thevane when the engine is running closing the fuel pump switch. The following is an explanation

of circuit operation.

Engine StartWhen the engine is cranking, current flows from the IG terminal of the ignition switch to the L1coil of the EFI main relay, turning the relay on. Current also flows from the ST terminal of theignition switch to the L3 coil of the circuit-opening relay, turning it on to operate the fuel pump.After the engine starts, the cylinders begin drawing in air, causing the measuring plate insidethe air flow meter to open. This turns on the fuel pump switch, which is connected to themeasuring plate, and current flows to the L2 coil of the circuit-opening relay.





Engine RunningAfter the engine starts and the ignition switch is turned from ST back to IG, current flowing to theL3 coil of the circuit-opening relay is cut off. However, current continues to flow to the L2 coil

while the engine is running due to the fuel pump switch inside the air flow meter being on. As aresult, the circuit-opening relay stays on, allowing the fuel pump to continue operating.

Engine StoppedWhen the engine stops, the measuring plate completely closes and the fuel pump switch isturned off. This cuts off the flow of current to the L2 coil of the circuit-opening relay. As a result,the circuit-opening relay goes off and the fuel pump stops operating.

Two Speed Fuel Pump ControlLarge displacement engines require a higher volume of fuel during starting and heavy loadconditions than small displacement engines. High capacity fuel pumps are used to meet the

demand, but they produce more noise and consume more power. To overcome thesedisadvantages and increase pump life, a two speed fuel pump control is used.

ON/OFF Two Speed Control w ith a Resistor This type uses a double contact relay and a series limiting resistor.





ON/OFF Two Speed Control wi th Fuel Pump ECU This type is similar to other systems, but uses a Fuel Pump ECU. In this system, however, ON-OFF control and speed control of the fuel pump is performed entirely by the Fuel Pump ECU

based on signals from the ECM. In addition, the Fuel Pump ECU is equipped with a fuel pumpsystem diagnosis function. When trouble is detected, signals are sent from the D1 terminal tothe ECM.

High SpeedDuring starting and heavy load condition, the ECM sends a HI signal (about 5 volts) to the FPCterminal of the Fuel Pump ECU. The Fuel Pump ECU then supplies full battery power to the fuelpump.

Low SpeedAfter the engine starts, during idle and light loads, the ECM outputs a low signal (about 2.5

volts) to the Fuel Pump ECU. Then, the Fuel Pump ECU supplies less voltage (about 9 volts) tothe fuel pump.

Three Speed Fuel Pump ControlWith this system, the fuel pump is controlled in 3 steps (high speed, medium speed, and low

speed).

High SpeedWhen the engine is operating under a heavy load at high RPM or starting, the ECM sends a 5volt signal to the fuel pump ECU. The fuel pump ECU then applies battery power to the fuelpump causing the fuel pump to operate at high speed.

Medium SpeedUnder heavy loads at low speed, the ECM sends a 2.5 volt signal to the fuel pump control. Thefuel pump ECU applies about 10 volts to the fuel pump. This is considered medium speed.





Low SpeedWhen idling or under light loads, the ECM sends a 1.3 volt signal to the fuel pump ECU. Thefuel pump ECU applies 8.5 volts to the fuel pump, preventing excessive noise and decreasing

power consumption.

Inertia Switch The fuel pump inertia switch shuts off the fuel pump when the vehicle is involved in a collision,minimizing fuel leakage.





Operation The inertia switch consists of a ball, spring loaded link, contact point, and reset switch. If theforce of the collision exceeds a predetermined value, the ball will move causing the springloaded link to drop opening the contact point. This opens the circuit between the ECM and FuelPump ECU causing the fuel pump to turn off. If the fuel pump inertia switch has been tripped, itcan be reset by pushing up on the reset switch for at least 1 second.





Pressure Regulators The pressure regulator must consistently and accurately maintain the correct fuel pressure. This is important because the ECM does not measure fuel system pressure. It assumes the

pressure is correct. There are two basic types of pressure regulators.

Modulated Pressure Regulators The return fuel delivery system uses a pressure regulator located on the fuel pressure railbetween the fuel pressure rail and the return line to the fuel tank. There are two types of pressure regulators. One type is modulated by vacuum, the other by atmospheric pressure.

Vacuum Modulated Pressure Regulator To maintain precise fuel metering, the vacuum modulated pressure regulator maintains aconstant pressure differential across the fuel injector. This means that fuel rail pressure willalways be at a constant value above manifold absolute pressure.





Low intake manifold pressure (idle for example) pulls on the diaphragm decreasing springpressure. This allows more fuel to return to the fuel tank decreasing pressure in the fuel rail.Opening the throttle increases manifold pressure. With less vacuum on the diaphragm spring

pressure will increase restricting fuel flow to the fuel tank. This increases pressure in the fuelrail.

Atmospheric Modulated Pressure Regulator The atmospheric modulated pressure regulator modifies fuel pressure with changes inatmospheric pressure. A hose is connected from the pressure regulator to the air intake hose

between the air filter and throttle plate. Spring pressure and atmospheric pressure keep thefuel pressure at a constant value, 226-265 kPa (38-44 psi). As air pressure changes, such asclimbing from low to high altitude, fuel rail pressure decreases because there is less force onthe diaphragm.





Constant Pressure Regulator Returnless Fuel Delivery System) The Returnless Fuel Delivery System uses a constant pressure regulator located above the fuelpump in the fuel tank. This type of regulator maintains a constant fuel pressure regardless of

intake manifold pressure. Fuel pressure is determined by the spring inside the regulator. Fuelfrom the fuel pump overcomes spring pressure and some fuel is bypassed into the fuel tank.Fuel pressure is non-adjustable.

High Temperature (Pressure Up) Fuel Pressure ControlSome engines are equipped with a high temperature fuel pressure control to prevent vapor lockfor easier starting and better driveability. A three way VSV is connected to the fuel pressureregulator vacuum line. Under normal conditions, the VSV is off and engine vacuum regulates

the pressure regulator. If the engine is started when the coolant temperature is 85'C (185'F) orhigher and the intake air temperature is above predetermined level, the ECM will turn on theVSV. Engine vacuum is closed off and atmospheric pressure is applied to the pressureregulator diaphragm. This increases fuel pressure preventing vapor lock. Once the engine isstarted, the VSV may remain on for about 120 seconds.





Fuel Delivery Components Fuel Lines And Connectors Today's vehicles use a variety of materials and connectors for fuel lines. Steel and syntheticmaterials are used, depending on location and model year. It is critical that the correct

procedures be followed when servicing the fuel lines.

Connectors can be the threaded type or the quick connector style.





Fuel Tank The fuel tank is designed to safely contain the fuel and evaporative emissions. Typically, ithouses the fuel pump assembly and rollover protection valves.

Fuel Filters Typically, there are two fuel filters in the fuel delivery system. The first filter is the fuel pump filterlocated on the suction side of the fuel pump. This filter prevents debris from damaging the fuelpump. The second filter, located between the pump and fuel rail, removes dirt andcontaminates from the fuel before it is delivered to the injectors. This filter removes extremelysmall particles from the fuel, the injectors require extremely clean fuel.

The filter may be located in the fuel tank as part of the fuel pump assembly or outside the tankin the fuel line leading to the fuel rail. The filter is designed to be maintenance-free with norequired service replacement.





A restricted fuel filter will prevent fuel from reaching the injectors. Therefore, the engine may behard starting, surge, or have low power under loads. A completely clogged filter will prevent theengine from starting.

Pulsation Damper The rapid opening and closing of the fuel injectors cause pressure fluctuations in the fuel rail. The result is that the amount of injected fuel will be more or less than the desired amount.Mounted on the fuel rail, the pulsation damper reduces these pressure fluctuations. Whenpressure suddenly begins to increase the spring loaded diaphragm retracts slightly increasingfuel rail volume. This will momentarily prevent fuel pressure from becoming too high. Whenpressure suddenly begins to drop, the spring loaded diaphragm extends, slightly decreasing

effective fuel rail volume. This will momentarily prevent fuel pressure from becoming too low.Not all engines require the use of a pulsation damper.

The screw mounted at the top of the damper provides an easy check for fuel system pressure.When the screw is up it means the fuel rail is pressurized. Under most conditions, this check isadequate. The screw is nonadjustable and it is used to calibrate the damper at the factory.





Fuel Injection Operation The fuel injector, when turned on by the ECM, atomizes and directs fuel into the intake manifold.

Fuel Injectors There is one injector per cylinder mounted in the intake manifold before the intake valve(s). Theinjectors are installed with an insulator/seal on the manifold end to insulate the injector fromheat and prevent atmospheric pressure from leaking into the manifold. The fuel delivery pipesecures the injector. An O-ring between the delivery pipe and injector prevents the fuel fromleaking.





Different engines require different injectors. Injectors are designed to pass a specified amountof fuel when opened. In addition, the number of holes at the tip of the injector varies withengines and model years. When replacing an injector it is critical that the correct injector beused.





Inside the injector is a solenoid and needle valve. The fuel injector circuit is a ground switchedcircuit, To turn on the injector, the ECM turns on a transistor completing a path to ground. Themagnetic field pulls the needle valve up overcoming spring pressure and fuel now flows out of the injector. When the ECM turns off the circuit, spring pressure will force the needle valve ontoits seat, shutting off fuel flow.





Injector Timing/Drive Circui ts The design of the injector drive circuit and ECM programming determines when each injector

delivers fuel in relation to the operating cycle of the engine. If the injectors are turned onaccording to the crankshaft position angle, it is called synchronous injection. That is, theinjectors are timed to turn on according to crankshaft position. Depending on engineapplication, the three main types of synchronous injection designs are: Simultaneous,Grouped, or Sequential. In all these types, voltage is supplied to the injectors from the ignitionswitch or EFI main relay and the ECM controls injector operation by turning on the drivertransistor grounding the injector circuit. Simultaneous and grouped are the oldest styles, andare no longer used.

On simultaneous, all injectors are pulsed at the same time by a common driver circuit. Injectionoccurs once per engine revolution, just prior to TDC No. 1 cylinder. Twice per engine cycle, one-

half of the calculated fuel is delivered by the injectors. With grouped drive circuits, injectors aregrouped in combinations. There is a transistor driver for each group of injectors. On sequentialdrive circuits, each injector is controlled separately and is timed to pulse just before the intakevalve opens.

There are times when the ECM needs to inject extra fuel into the engine regardless of crankshaft position and this is called asynchronous injection. Asynchronous injection is whenfuel is injected into all cylinders simultaneously when predetermined conditions exist withoutrelation to the crankshaft angle. Two common conditions are starting and acceleration.

FUEL SYSTEMS #2 - INJECTION DURATION CONTROLS




Note: The EWD injector circuit can identify if the injection system is a grouped or sequential. Asequential system will have one injector per injector driver.

Fuel Injection Volume Control The amount of fuel injected depends on fuel system pressure and the length of time the injector

is turned on. Fuel system pressure is controlled by the pressure regulator, and injector on timeis controlled by the ECM. The time the injector is on is often called duration or pulse width, andit is measured in milliseconds (ms). Cold starting requires the highest pulsewidth. Pulsewidthis dependent primarily on engine load and engine coolant temperature. The higher the engineload and the more the throttle is opened to let air in, the greater pulsewidth increases. The ECMdetermines the duration based on the input sensor signals, engine conditions, and itsprogramming.





Start ModeWhen the ignition switch is in the Start position, the ECM receives a voltage signal at the STAterminal. The ECM determines basic injection duration based on the ECT (THW) signal. OnMAP sensor equipped engines the ECM will then modify this duration based on the IAT (THA)signal.





The ECM will adjust the duration based on battery voltage. During cranking, battery voltage ismuch lower causing the injector valve to lift slowly. The ECM corrects for this by increasinginjection duration.

When the ECM receives the NE signal (Crankshaft Position Sensor), all the injectors are turnedon simultaneously. This insures there is enough fuel for starting the engine. Note that belowfreezing, injection duration increases drastically to overcome the poor vaporizationcharacteristics of fuel at these temperatures.

Engine Running (After Start) Injection Duration Control

Total fuel injection duration is determined in three basic steps:

• Basic injection duration.

• Injection corrections.

• Voltage correction.

Basic injection duration is based on air volume and engine RPM. Air volume on MAF equippedengines is determined by the MAF voltage signal.





On MAP sensor equipped engines, the ECM calculates air volume based on the PIM signal,engine RPM, THA signal, and volumetric efficiency values stored in the ECM.

Injection corrections adjust the basic injection duration to accommodate different enginemodes and operating conditions. It is based on a variety of input signals.

Voltage correction adjusts the injection duration to compensate for differences in the electricalsystem voltage.

After Start Enr ichmentImmediately after starting (engine speed above a predetermined level), the ECM supplies anextra amount of fuel for a certain period of time to stabilize engine operation.

This correction volume is highest immediately after the engine has started and graduallydecreases. The maximum correction volume value is based on engine coolant temperature. The hotter the engine, the less volume of fuel injected.

Warm-Up EnrichmentA rich fuel mixture is needed to maintain driveability when the engine is cold. The ECM injects

extra fuel based on engine coolant temperature. As the engine coolant warms up, the amountof warm-up enrichment decreases. Depending on the engine, warm-up enrichment will end atapproximately 50'C-80'C (122'F-176’F).

If the ECM is in Fail-Safe Mode for DTC PO 115, the ECM substitutes a temperature value,usually 80'C (176'F).





Correction Based on Intake Air Temperature (MAP Sensor Equipped Engines) The density of the intake air decreases as temperature increases. Based on the IAT (THA)signal, the ECM adjusts the fuel injection duration to compensate for the change in air density. The ECM is programmed so that at 20'C (68'R no correction is needed. Below 20'C (68'F),

duration is increased, above 20'C (68'F), duration is decreased.

If the ECM is in Fail-Safe Mode for DTC P0110, the ECM substitutes a temperature value of 20'C(68’F).

Power Enrichment CorrectionWhen the ECM determines the engine is operating under moderate to heavy loads, the ECMwill increase the fuel injection duration. The amount of additional fuel is based on the MAF orMAP sensors, TPS, and engine RPM. As engine load (and air volume) increases, fuel injectionduration increases. As engine RPM increases, injection frequency increases at the same rate.

Acceleration CorrectionOn initial acceleration, the ECM extends the injection duration richening the mixture to prevent astumble or hesitation. The duration will depend on how far the throttle valve travels and engineload. The greater the throttle travel and engine load, the longer the injection duration.





Deceleration Fuel CutDuring closed throttle deceleration periods from moderate to high engine speeds, fuel deliveryis not necessary or desirable. To prevent excessive decel emissions and improve fueleconomy, the ECM will not open the injectors under certain decel conditions. The ECM willresume fuel injection at a calculated RPM.

Referring to the graph, fuel cut-off and resumption speeds are variable, depending on coolanttemperature, A/C clutch status, and the STA signal. Essentially, when extra engine loads arepresent, the ECM will begin fuel injection earlier.

Fuel Tau Cut is a mode employed on some engines during long deceleration time with thethrottle valve closed. During these times, excess oxygen would enter the catalytic converter. Toprevent this, the ECM will very briefly pulse the injectors.

Engine Over-Rev Fuel Cutoff To prevent engine damage, a rev-limiter is programmed into the ECM. Any time the engine RPMexceeds the pre-programmed threshold, the ECM shuts off the injectors. Once RPM falls belowthe threshold, the injectors are turned back on. Typically, the threshold RPM is slightly above theengine's redline RPM.

Vehicle Over-Speed Fuel Cutoff On some vehicles, fuel injection is halted if the vehicle speed exceeds a predeterminedthreshold programmed into the ECM. Fuel injection resumes after the speed drops below thisthreshold.





Battery Voltage Correction The applied voltage to the fuel injector will affect when the injector opens and the rate of opening. The ECM monitors vehicle system voltage and will change the injection on time signalto compensate. If system voltage is low, the injection on time signal will be longer, but theactual time the injector is open will remain the same (if system voltage were higher).





EVAP Purge CompensationWhen the evaporative purge valve is on, fumes from the charcoal canister are drawn into theintake manifold. The ECM will compensate based on the oxygen sensor output and shorten theinjector pulse width.





ASSIGNMENT NAME: ___________________________

1. Explain in detail both Grouped Injection and Sequential Injection?

2. What inputs are use for Injection Duration control during “After start”?

3. Explain detail “Afterstart Enrichment Correction”

4. Explain in detail “Warm-Up Enrichment Correction”

5. Explain explain the “Fuel Correction” based on Intake Air Temperature (MAP sensorequipped engines:

6. Explain in detail “Power Enrichment Correction”





7. Explain in detail “Acceleration Enrichment Correction”

8. Explain in detail “Deceleration Fuel Cut”

9. Explain in detail the “Engine Over-Rev Fuel Cutoff”

10. Explain in detail “Vehicle Over-Speed Fuel Cutoff”

11. Explain in detail “Battery Voltage Correction”

12. Explain in detail “EVAP Canister Purge Compensation”





Closed Loop Systems

A system that controls its output by monitoring its output is said to be a closed loop system. Anexample of a closed loop system is the vehicle's charging system. The voltage regulatoradjusts the voltage output of the alternator by monitoring alternator voltage output. If voltage istoo low, the voltage regulator will increase alternator output. Without the voltage regulator,alternator output could not be adjusted to match the electrical loads. Many systems are closedloop systems. Some other examples are: cruise control, ignition system knock control, idlespeed control, and closed loop air/fuel ratio correction control. When the ECM corrects theair/fuel ratio based on the oxygen or air/fuel ratio sensor, the system is said to be in closedloop.

Open Loop Systems

An open loop system does not monitor its output and make adjustments based on its output. The temperature control in a vehicle not equipped with automatic air conditioning serves as anexample.

Closed Loop Fuel Control The ECM needs to monitor the exhaust stream and adjust the air/fuel ratio so that the catalyticconverter will operate at peak efficiency, reducing regulated emission gases. Measuring theamount of oxygen remaining after combustion is a means to indicate the air/fuel ratio. A richermixture will consume more oxygen during combustion than a leaner mixture. The oxygensensor or air/fuel ratio sensor measures the amount of oxygen remaining after combustion inthe exhaust stream. From this information, the ECM will control the injection duration to achievethe desired, ideal air/fuel ratio of 14.7: 1. This is necessary so the catalytic converter will operateat peak efficiency.

Note: The engine operation often requires different air/fuel ratios for starting, maximum power,and maximum fuel economy. The 14.7:1 ratio is for catalytic converter efficiency.

FUEL SYSTEMS #3 - CLOSED LOOP / FUEL TRIM




Stoichiometry and Catalyst EfficiencyFor the catalytic converter to operate at peak efficiency, the air/fuel ratio must be at the idealstoichiometric ratio of 14.7 parts air to one part fuel as measured by weight. This why the ECMtries to maintain a 14.7 to I ratio whenever possible.





Open Loop Mode The ECM will be in open loop mode when:

• starting the engine.

• the engine is cold.

• hard acceleration.

• during fuel cut-off.

• wide open throttle.

If the engine will not go into closed loop mode, the problem may be insufficient enginetemperature, no response from the oxygen sensor or air/fuel sensor, or the heater circuit isinoperative. Usually, no response from the oxygen or A/F sensor will set DTC P0125.

If there is a driveability problem only in closed loop, anything that disrupts air/fuel ratio, theoxygen or A/F sensor circuit may be the cause.





Closed Loop Operation/Oxygen Sensor When in closed loop, the ECM uses the oxygen sensor voltage signal to make minorcorrections to the injection duration. This is done to help the catalytic converter operate at peakefficiency.

When the voltage is higher than 450 mV, the air/fuel ratio is judged to be richer than the idealair/fuel ratio and the amount of fuel injected is reduced at a constant rate. The reduction in the

duration continues until the oxygen sensor signal switches to a low voltage (lean air/fuel ratio).





When the voltage signal is lower than 450 mV, the air/fuel ratio is judged to leaner than theideal air/fuel ratio so the amount of fuel injected is increased at a constant rate. The increase induration continues until the oxygen sensor switches to high voltage (rich air/fuel ratio). At this

point, the ECM will slowly decrease the amount of fuel, therefore the air/fuel ratio oscillatesslightly richer or leaner from the ideal air/fuel ratio. The result is an average of approximately14.7: 1. This produces the proper mixture of exhaust gases so that the catalytic converteroperates at its most efficient level.

The frequency of this rich/lean cycle depends on exhaust flow volume (engine RPM and load),the oxygen sensor response time, and the fuel control programming. At idle, exhaust flowvolume is low, and the switching frequency of the oxygen sensor is low. As engine speedincreases, the switching frequency of the oxygen sensor increases, generally eight or moretimes at 2,500 RPM in ten seconds.

Closed Loop Operation Air/Fuel Sensor With an A/F sensor, air/fuel mixture correction is faster and more precise. An oxygen sensorsignal voltage abruptly changes at the ideal A/F ratio and changes very little as the air/fuel ratioextends beyond the ideal ratio. This makes fuel control less precise, for the ECM mustgradually and in steps change the injection duration until the oxygen sensor signal abruptlyswitches.

By contrast, the A/F sensor outputs a voltage signal that is relatively proportional to the A/F ratio. The ECM now knows how much the A/F ratio has deviated from the ideal, and thus, the fuelcontrol program can immediately adjust the fuel injection duration. This rapid correctionreduces emission levels because the ECM can more accurately maintain the ideal air/fuel ratio

for the best catalytic converter efficiency.

Therefore, when observing A/F sensor voltage output, the output is relatively constant becausethere is no cycling between rich and lean.

Fuel TrimAs the engine and sensors change over time, the ECM needs a method to adjust the injectionduration for improved driveability and emission performance. Fuel trim is a program in the ECMdesigned to compensate for these changes.

When in closed loop, the ECM modifies the final injection duration based on the oxygen sensor.

These minor corrections are needed to maintain the correct air/fuel ratio. However, if morecorrection than normal (as determined by the ECM) is needed, the ECM will use the fuel trimstrategy to compensate. Fuel trim allows the ECM to learn and adjust the injection





duration quickly by reducing the correction time back to normal. This means that driveability andperformance will not suffer.

Fuel trim can be observed on the Diagnostic Tester as a percentage. A positive percentagemeans that the ECM has increased the duration and a negative percentage means the ECMhas decreased the duration.

There are two different fuel trim values that affect final injection duration and can be observed bythe technician; short term fuel trim (SHORT FT) and long term fuel trim (LONG FT). SHORT FTis a temporary addition or subtraction to the basic injection duration. LONG FT is part of thebasic injection duration calculation and it is stored in the ECM's memory.

SHORT FTSHORT FT is based on the oxygen sensor, and therefore, it only functions in closed loop.

SHORT FT responds rapidly to changes in the oxygen sensor. If SHORT FT is varying close to0%, little or no correction is needed. When SHORT FT percentage is positive, the ECM hasadded fuel by increasing the duration. A negative percentage means the ECM has subtractedfuel by decreasing the duration. The SHORT FT value is temporary and not stored when theignition key is turned off.

SHORT FT is used to modify the long term fuel trim. When the SHORT FT remains higher orlower longer than expected, the ECM will add or subtract this value to the LONG FT.

LONG FTLONG FT is stored in memory because it is part of the basic injection duration calculation. The

ECM uses the SHORT FT to modify the LONG FT. The LONG FT does not react rapidly tosudden changes, it only changes when the ECM decides to use the SHORT FT value to modifythe LONG FT. LONG FT is stored in the ECM's memory and it is not erased when the ignitionkey is turned off. Because LONG FT is part of the basic injection duration, it affects injectionduration in closed and open loop. Like the SHORT FT, when LONG FT is at 0% there has beenno modification to the basic injection duration. A positive percentage means the ECM is addingfuel; a negative percentage, subtracting fuel.

Fuel System Monitor The fuel system monitor is designed to set a DTC if the fuel injection system is going to exceedemission standards. This monitor uses the fuel trim correction levels for detection. The amount

of fuel trim correction that will set a DTC varies with each engine type and model year.





ASSIGNMENT NAME: ___________________________

1. Explain in detail Open Loop Operation?

2. Explain in detail Closed Loop Operation?

3. Explain the relationship between “Stiochometric Fuel Ratio” and “Catalytic Converterefficiency”:

4. List the five engine conditions when the ECM will be in “Open Loop Mode”:

5. Explain in detail how the ECM uses the Oxygen Sensor to control fuel duration:

6. Explain the term “Fuel Trim”

7. Explain in detail both “SHORT Fuel Trim” and “LONG Fuel Trim”;





OBD (On-Board Diagnostic System, Generation 1)In April 1985, the California Air Resources Board (CARB) approved On-Board Diagnosticsystem regulations, referred to as OBD. These regulations, which apply to almost all 1988 and

newer cars and light trucks marketed in the State of California, require that the engine controlmodule (ECM) monitor critical emission related components for proper operation andilluminate a malfunction indicator lamp (MIL) on the instrument panel when a malfunction isdetected. The OBD system also provides for a system of Diagnostic Trouble Codes (DTC) andfault isolation logic charts in the repair manual, to assist technicians in determining the likelycause of engine control and emissions system malfunctions. The basic objectives of thisregulation are twofold:

• To improve in-use emissions compliance by alerting the vehicle operator when amalfunction exists.

• To aid automobile repair technicians in identifying and repairing malfunctioning circuits in

the emissions control system.

OBD self diagnosis applies to systems which are considered to be most likelyto cause a significant increase in exhaust emissions if a malfunction occurs.Most notably, this includes:

• All major engine sensors• The fuel metering system• Exhaust gas recirculation (EGR) function

OVERVIEW OF OBD AND REGULATIONS




Malfunct ion Indicator Light (MIL)When a malfunction occurs, the MIL remains illuminated as long as the fault is detected andgoes off once normal conditions return, leaving a Diagnostic Trouble Code (DTC) stored in the

ECM memory. Circuits are monitored for continuity, shorts, and in some cases, normalparameter range.

The Malfunction Indicator Light (MIL) is also a visual inspection item in most emissionsinspection and maintenance programs U/M), allowing the emissions inspector to make a quickvisual determination whether the engine control/emissions system is functioning normally.During the visual inspection phase of the I/M test, the inspector must observe the MIL during a"key on bulb check" and again with the engine running. The MIL should be on during the bulbcheck and go off when the engine starts. When a vehicle passes this check, it is highlyprobable that the engine control system is functioning normally.

Although the OBD regulation applies only to California emissions certified vehicles, some or allof the OBD system features are found on Federal emissions certified vehicles as well.

OBD Diagnostic Trouble Codes (DTC)Diagnostic Trouble Codes or DTCs are generated by the on-board diagnostic system andstored in the ECM memory. They indicate the circuit in which a fault has been detected. DTCinformation remains stored in the ECM long term memory regardless of whether a continuous(hard) fault or intermittent fault caused the code to set. Toyota products with OBD will continueto store a DTC in the ECM long term memory until the code is cleared by removing power fromthe ECM BATT terminal. In most cases, the EFI fuse powers this keep alive memory.





Serial Data StreamsAlthough not required by the OBD regulation, the use of serial data accessible by special scantools, has been introduced by some manufacturers. Serial data is electronic information about

sensors, actuators, and ECM fuel/spark strategy, which is accessed from a single wire comingfrom the ECM. The term serial data implies that the information is digitally coded andtransmitted in a series of data words . The data words are decoded and displayed by a scantool.

The typical Toyota OBD serial data stream consists of up to 20 data words including sensorvalues, switch status, actuator status, and other engine operating data.

OBD-II (On-Board Diagnostic System, Generation 2)Although OBD supplies valuable information about a number of critical emissions relatedsystems and components, there are several important items which were not incorporated intothe OBD standard due to technical limitations at the time that the system was phased intoproduction (during the 1988 model year.) Since the introduction of OBD, several technicalbreakthroughs have occurred. For example, the technology to monitor engine misfire andcatalyst efficiency has been developed and implemented on production vehicles.





OBD-II (On-Board Diagnostic System, Generation 2) Cont inuedAs a result of these technical breakthroughs and because existing I/M programs have proven tobe less effective than desired in detecting critical emissions control system defects which occur

during normal road load operation, a more comprehensive OBD system was developed underthe direction of CARB.

OBD-II, which is implemented over the 1994 through 1996 model years, adds catalyst efficiencymonitoring, engine misfire detection, canister purge system monitoring, secondary air systemmonitoring, and EGR system flow rate monitoring. Additionally, a serial data stream consistingof twenty basic data parameters and diagnostic trouble codes is a required part of thediagnostic system.

In addition to the basic required OBD-II data stream, Toyota has an enhanced data streamwhich consists of approximately 60 additional data words. Access to all OBD-II data is made by

connecting a generic scan tool to a standardized Data Link Connector (DLC) located under theleft side of the instrument panel. The standards for data, the scan tool, diagnostic test modes,diagnostic trouble codes, and everything related to the introduction of the OBD-II regulation areestablished by the Society of Automotive Engineers.

The goal of the OBD-II regulation is to provide the vehicle with an on-board diagnostic systemwhich is capable of continuously monitoring the efficiency of the emissions control system, andto improve diagnosis and repair efficiency when system failures occur. In essence, anemissions I/M station will be programmed into every OBD-II equipped vehicle.

OBD-II Features

The following information will familiarize you with the highlights of the OBD-II system features:

Oxygen Sensor (02S) DiagnosticsEnhanced diagnostics for the oxygen sensor(s) include monitoring for degradation andcontamination by monitoring switching frequency and lean-rich, rich-lean switch time.

Fuel System MonitoringMost fuel systems continually shift their base calibration to compensate for changes inatmospheric pressure, temperature, fuel composition, component variations, and other factors. This adaptive behavior is normal as long as it remains within the design limits of the system.

When conditions occur which cause the fuel system to operate outside of its designparameters, for example, a skewed air flow meter signal, incorrect fuel pressure, or othermechanical problems, the OBD-II system is designed to detect this abnormal operatingcondition. If the condition occurs for longer than a specified amount of time, a DTC will bestored. When a DTC stores, the engine speed, load, and warm-up status is stored in aretrievable serial data freeze frame.





Misfire MonitoringBy using a high frequency crankshaft position signal, the ECM can closely monitor crankshaftspeed variations during individual cylinder power strokes. When an engine is firing cleanly on

all cylinders, the crankshaft speeds up with each power stroke. When misfire occurs,crankshaft speed increase is effected for that cylinder.

Toyota OBD-II engines use a 36 minus 2 tooth Ne sensor which directly measures crankshaftspeed and position. This information is processed by the ECM to determine if misfire occurs,which cylinder it is occurring in, and the degree of misfire.

When a misfire of any significance is detected, a DTC is stored and the engine speed, load andwarm-up status at the time of misfire will be stored. Additionally, the vehicle operator will bealerted to the condition by a rapidly flashing MIL during periods when significant misfire isoccurring.





Catalyst MonitoringA sub-oxygen sensor (S2) placed downstream, at the outlet of the catalytic converter, ismonitored for switching frequency and compared to the switching frequency of the main oxygen

sensor (S1), placed upstream of the catalyst. The oxidation efficiency of the catalyst can bedetermined by comparing the switching frequency of these two sensors. As the catalystconversion efficiency declines, the switching frequency of sensor 2 increases, approaching thatof sensor 1. In addition to being used for diagnostics, sensor 2 also assists in maintainingoptimum fuel control when the catalyst begins to degrade.

EGR System MonitoringEnhanced monitoring of EGR flow rate characteristics include the ability to detect flow rateswhich are above or below the design flow rate for a given engine operating condition. Onemethod of accomplishing this is to simply monitor the change in temperature on the intake sideof the EGR passage. Another method is to measure the degree of rich correction to the fueldelivery system as EGR flow is momentarily inhibited.





Evaporative Purge System MonitoringBy monitoring the oxygen sensor and injection pulse width as the canister is being purged, theECM can detect the reduction of exhaust oxygen content and corresponding decrease in

injection pulse width to correct for this momentary rich condition. In this manner, the ECM candetect a failure in the canister purge control system and store a DTC to alert the vehicleoperator of the malfunction. Purge flow monitoring is only used on 95 and later OBD-Il equippedvehicles.

Secondary Air System MonitoringBy switching secondary air upstream of the oxygen sensor momentarily during closed loopoperation, the ECM can monitor the oxygen sensor response and corresponding injectionpulse width increase to determine if the secondary air system is functioning normally.

Malfunction Indicator Light Illumination

Once a malfunction has been established (two trip detection logic where applicable) the MILwill illuminate and remain illuminated even if the condition is intermittent. The MIL will remainon after subsequent restarts even if the malfunction condition is no longer present. The OBD-IIsystem can only extinguish the MIL if the malfunction does not reoccur during three subsequentsequential trip cycles.

The OBD-II system can only erase a stored DTC if the malfunction is not detected during fortysequential trip cycles. Toyota systems do not erase the code, but rather place a flag on anycode which does not reoccur during 40 subsequent trip cycles.

DTCs can be erased using the generic scan tool or by removing power from the ECM BATT

terminal.

Readiness Test The OBD-II diagnostic system continually monitors for misfire and fuel system faults. It alsoperforms a functional test on the catalyst, EGR system, and oxygen sensors once during everydriving cycle or "trip ". Certain driving conditions must be encountered before these systemscan be confirmed as operating normally. For example, the engine must be fully warmed up,throttle angle must have exceeded a specified angle, the engine must have achieved aspecified load, and so on.

In the event that these driving conditions have not been met, the ECM will not have completed

its "readiness test", and is not capable of displaying supported test data. Under theseconditions, the scan tool will display a message indicating that "not all supported readinesstests are complete", warning the operator that this test data is not available.





Readiness Test Continued The readiness test is a flag which is used during I/M inspections to indicate that the vehicle on-board diagnostic system cannot supply information required during the test. In this case, the

vehicle must be operated until all readiness testing conditions have been satisfied.





Stored Engine Freeze Frame DataUpon detection of a malfunction, the OBD-II system will store all data at the time that the DTCset. This freeze frame data can be retrieved using the generic scan tool.

Standardization of Service Information and DTCsUnder the provisions of OBD-II regulations, emissions related diagnostic and service

information will be readily available to the service industry, from the vehicle manufacturer. Thisinformation includes procedures and specifications necessary to diagnose the engine controlsystem. Although enhanced diagnostics may be available using special equipment andprocedures, at a minimum, repair procedures will be written using the generic scan tool andother commonly available test equipment like multimeters; and oscilloscopes.

In an effort to simplify diagnostics, OBD-II requires that all manufacturers standardize DTCs onOBD-II equipped vehicles. Eventually, all emissions related service information will bestandardized in format and available through an electronic media.





Clean Air Act Amendments of 1990On November 15, 1990, the Clean Air Act was amended, directing the Environmental ProtectionAgency (EPA) to promote new regulations, under section 207(a), requiring automobile

manufacturers to install on-board diagnostic systems capable of.• Identifying deterioration or malfunction of major emissions components which could

result in vehicle failure to comply with federal emissions standards.• Alerting the vehicle operator of the need to maintain and/or repair emissions related

components and/or systems.• Storing DTCs and providing access to vehicle on-board information.

Additionally, manufacturers will:• Make available to all interested parties, all necessary emissions maintenance and repair

information.

Adoption of these provisions was prompted by the fact that in 1990, 96urban areas in the U.S. were in violation of National Ambient Air QualityStandards (NAAQS) for ozone and 41 areas for carbon monoxide.

Although CAAA'90 regulations vary slightly from CARB OBD-II, EPA has elected to adoptCalifornia OBD-II for Federal emissions certification, effective with the '96 model year.Beginning in the '98 model year, a new Federal OBD standard will be adopted, effectivelyeliminating the different status between California and Federal emissions certification.





What is Serial Data?Serial data is electronically coded information which is transmitted by one computer andreceived and displayed by another computer. Using an analog/digital circuit, the transmitting

computer digitizes the data from sensors, actuators, and other calculated information. Typically,this means that each sensor or actuator value is converted into a one byte (8 bits) binary wordbefore it is transmitted to the receiving computer.

In order to display the data in familiar units that you are used to working with, the receivingcomputer interprets each binary word as it is received and displays it as an analog voltage,temperature, speed, time, or other familiar unit of measurement.

Serial data gets its name from the fact that data parameters are transmitted, one after another,in series. The display on the receiving computer updates or refreshes once each data cycle,after all data has been received. Therefore the refresh rate of the data is determined by how

many words are on the data stream and how quickly the data is transmitted.

The data transmission rate is referred to as the baud rate. Baud rate refers to the number of data bits that can be transmitted per second. For example, if a data stream has 12 parameters,and each parameter is converted into an 8 bit data word, the total size of the data transmissionis 96 bits of data (12 words x 8 bits per word.) If this data can be transmitted once every second,the baud rate is 96 bits/second or 96 baud. In this case, the display screen will refresh datavalues once every second.

SERIAL DATA




In the case of Toyota engine control systems, there are three different types of serial data whichcan be received and displayed by your Diagnostic Tester, depending on application. These areOBD, OBD-II, and V-BoB. In all three cases, data is digitized by the transmitting computer (ECM

or V-BoB) and displayed by the Diagnostic Tester. The main difference between these threedata sources are the specific parameters available on the data stream and the speed at whichdata can be transmitted and refreshed on the Diagnostic Tester display.

SERIAL DATA




Displaying Engine Data The type of serial data available depends on the vehicle you are working on. Many Toyotavehicles with OBD, manufactured since 1989, have a serial data stream available on the VF1

terminal of DLC 1 (Check connector) or the ENG terminal of DLC 2 (TDCL).

Vehicles which support a serial data stream can be identified by the presence of a TE2 circuit(see the application matrix on page 86 of this handbook). Depending on the vehicle, there canbe as many as 20 different sensor, actuator, and diagnostic data parameters represented onthe OBD data stream.

The OBD-II system, which phased in during the 1994 through 1996 model years, has a highspeed data stream available on terminal 2 of DLC 3 01962 connector). There are in excess of 50 data parameters represented on the OBD-II engine data stream.

Accessing serial data on any of these vehicles is a simple matter using the Diagnostic Tester.

SERIAL DATA




For 1989 and later models which do not support serial data streams, the Vehicle Break-out Boxgives you the ability to create one. By connecting the V-BoB in series with the ECM, informationfrom every wire can be serialized and displayed by the Diagnostic Tester. Although it takes a

little bit longer to install the V-BoB, the unlimited amount of high speed data makes the effortwell worth the time invested.

SERIAL DATA




The OBD Diagnostic Circui t This unidirectional data stream typically consists of 14 to 20 data words representing primarilysensor inputs and three outputs; injection pulse width, spark advance angle, and idle speed

control command. Data is transmitted at a rate of 100 baud, updating on the Diagnostic Testerdisplay approximately once every 1.25 seconds. Depending on application, the data isaccessed from either DLC 1 or DLC 2. Data is triggered by grounding the TE2 circuit andreading the VF1 circuit.

Diagnostic Trouble Codes can be displayed using the Diagnostic Tester or by grounding the TE1 circuit and counting the Malfunction Indicator Lamp (MIL) flashes. The scan tool readscodes by counting the low voltage pulses on the W terminal of the Diagnostic Link Connector(DLC). Therefore, code retrieval is a relatively slow process, especially when multiple codes arestored.

SERIAL DATA




The OBD-II Diagnostic Circui t The OBD-II data line is a bi-directional communication link which is capable of transmitting andreceiving data. This feature allows the Diagnostic Tester to operate system actuators and send

commands to the ECM in addition to displaying system data.

The high speed OBD-II data stream typically consists of 50 to 75 data words representingvirtually all sensor inputs, actuator outputs, several calculated parameters, many fuel feedbackrelated parameters, and cylinder misfire data. The data is transmitted at a rate of 10.4 Kilobaud, giving the Diagnostic Tester a display refresh rate capability of approximately once every200 milliseconds.

Data is accessed from DLC 3, terminal 2. It is triggered by a communication signal generatedby the Diagnostic Tester when any OBD-II function has been selected.

On OBD-Il vehicles, the scan tool reads DTCs directly from the serial data stream, therefore,codes are displayed almost instantly. Codes can only be retrieved and displayed using theDiagnostic Tester or an equivalent J 1978 scan tool.

SERIAL DATA




SERIAL DATA




Uses and Limitations o f Scan Tool Serial Data for DiagnosisA scan tool is an exceptionally useful tool when diagnosing engine control system problems. Itgives you access to vast quantities of information from a conveniently located diagnostic

connector.

• A scan tool allows a "quick check" of sensors, actuators, and ECM calculated data. Forexample, when checking for sensor signals which may be shifted out of normal range,scan data allows you to quickly compare selected data to repair manual specificationsor known good vehicle data.

• When checking for intermittent fault conditions, it provides an easy way to monitor inputsignals while wiring or components are manipulated, heated, and cooled.

There are, however, several important limitations you need to consider when attempting to

diagnose certain types of problems using serial data.

• Serial data is processed information rather than a live signal. It represents what the ECM"thinks" it is seeing rather than the actual signal which would be measured at the ECMterminal. Serial data can also reflect a signal value the ECM has defaulted to, rather thanthe actual signal.

For example, with OBD, the Engine Coolant Temperature sensor data displayed with an opencircuit is the failsafe value of 176’F. If the actual voltage was measured at the THW terminal of the ECM, it would be 5 volts, equivalent to -40'F.

SERIAL DATA




In the case of output commands, serial data represents the calculated output, not necessarilywhat the circuit driver is doing. For example, when cranking an engine which is in fuel cutfailsafe (due to an open IGf line), calculated injection pulse is displayed on serial data even

though the injector driver is not being operated.

Using serial data to troubleshoot intermittent problems also has its limitations because of datatransmission speed.

When the data refresh rate is slow, as it is with slower baud rate data streams, it is easy tomiss changes which occur in a signal between display updates. As a result, intermittent signalproblems are often not detected on a slow serial data stream.

For example, a Throttle Position Sensor signal wire that goes open circuit every time the vehicledrives over a bump. If the open condition does not last for at least 1.25 seconds, there is a goodpossibility that the change in signal value will go undetected by your scan tool.

When troubleshooting intermittent problems on vehicles without high speed serial data (likeEnhanced OBD-II), it is much better to use serial data generated by V-BoB than to use the OBDserial data. It takes more time to connect V-BoB to the ECM, but if an intermittent problem

occurs, the high speed serial data generated by V-BoB will catch the fault.

Given this information, it is clear that care must be exercised when interpreting serial data andusing it to make diagnostic decisions. Once you are familiar with irregularities like these, therisk of diagnostic error is significantly reduced.

SERIAL DATA




Serial Data InterpretationUsing and interpreting serial data may seem confusing at first because there is so much data.Some of the data uses unfamiliar names, and some of it is displayed in unfamiliar units. To

help you become familiar with the new terminology and what each data parameter means, referto appendices A & B of this handbook. They provide detailed definitions, specifications, and anexplanation of each data parameter available on OBD, OBD-II, and V-BoB data streams.

ECM Strategy for Fuel and Spark Control Troubleshooting driveability problems can be complicated, especially when there is so muchdiagnostic data available. You may sometimes find it difficult to decide which information isimportant and which information you should ignore. The key is getting back to the basics. Thatmeans the basic theory and the basic data.

As you have learned, fuel and spark calculation are, for the most part, affected by only a few

input sensors. In fact, basic injection and spark calculation are a function of just two sensors;the engine speed and engine load sensors.

There are only four other sensors which have significant effects on injection (and to a lesserdegree on spark advance corrections); those are engine coolant temperature, intake airtemperature, throttle angle, and oxygen sensor feedback.

Data analysis is much easier once you are familiar with these six input parameters, their unitsof display, and their nominal values.

Six Important Sensor Inputs

The six major sensor inputs which have the most impact on fuel and spark calculations are, inorder of importance:

• Engine Load- Vane Air Flow meter- Karman Vortex Air Flow meter- Mass Air Flow meter- Manifold Absolute Pressure sensor

• Engine Speed-Engine rpm (Ne) sensor

• Engine Coolant Temperature

-Engine Coolant Temperature sensor• Throttle Position

- Throttle Position sensor- Closed Throttle Position switch

• Intake Air Temperature-Intake Air Temperature sensor

• Exhaust Oxygen:-02 Sensor

SERIAL DATA INTERPRETATION




Fuel Trim To better understand how oxygen feedback and learned corrections are determined, a brief review of injection theory is in order.

Review of Injection Duration TheoryFinal fuel injection duration is a function of three steps:

• Basic injection duration• Duration corrections for operating conditions• Battery voltage correction

Basic injection duration is based on engine load, speed, and a correction factor called fuel trim.Duration corrections for operating conditions are based on the sensors listed below. These areadjustments to the basic injection duration based on changing operating conditions.

• Engine Coolant Temperature (ECT)• Throttle Position (TP)• Intake Air Temperature (IAT)• Exhaust Oxygen (02S)

Battery voltage correction is an adjustment to the final injection duration to account for variationsin injector opening time caused by changing operating voltage.





Calculation of Basic Injection Duration The first step in determining how much fuel to deliver to the engine is calculation of basicinjection duration. Basic injection duration is a function of:

• Engine load (VAF, MAF, or MAP)• Engine speed (Ne)• Long fuel trim (LFT) correction factor

This basic injection duration value is the ECM's best guess at the actual injection timenecessary to achieve an ideal air/fuel ratio. Generally, this basic injection calculation is veryaccurate, typically within ±20% of what actual injection needs to be. Once within this range, theECM can trim the air/fuel ratio to stoichiometry based on oxygen sensor information.

Oxygen Feedback CorrectionDepending on many different factors, the amount of correction required for 02S feedback will

vary. If the amount of necessary correction remains relatively small, for example less than 10%,the ECM can easily adjust the mixture. As 02S feedback correction approaches the ±20% limit,the ECM fuel correction range becomes limited.





Oxygen Feedback Correction ContinuedWhen the amount of necessary correction becomes excessive, the ECM has a "learnedmemory" to adjust or "trim" the basic injection calculation. By increasing or decreasing basic

injection duration, 02S corrections can be held within an acceptable range, maintaining theECM ability to correct over a wide air/fuel ratio range.

Fuel Trim Impact on Injection DurationFuel trim is a term used to describe the percentage of correction to injection duration based onoxygen feedback. There are two different fuel trim values which affect final injection duration;long fuel trim (Long FT) and short fuel trim (Short FT).

Long FT is part of the basic injection duration calculation. It is determined by how closely thefuel system achieves the design air/fuel ratio.

Long FT is a learned value which gradually changes in response to factors beyond the controlof system design. For example, fuel oxygen content, engine wear, air leaks, variations in fuelpressure, and so forth.

Short FT is an addition to (or subtraction from) basic injection duration. Oxygen sensorinformation tells the ECM how close it comes to design air/ fuel ratio and the Short FT correctsfor any deviation from this value.

How Short FT WorksShort FT is a temporary correction to fuel delivery which changes with every cycle of the oxygensensor. Under normal conditions, it fluctuates rapidly around its ideal value of 0% correction

and is only functional during closed loop operation.

Short FT is a parameter on the OBD-Il data stream, that can be displayed on the Diagnostic Tester. Its normal range is ±20%, but under normal operating conditions, rarely goes beyond ±10%.

Short FT responds to changes in 02S output. If basic injection duration results in a lean air/fuelratio, Short FT responds with positive corrections (+1% to +20%) to add fuel or enrich themixture. If basic injection is too rich, Short FT responds with negative corrections (-I% to -20%)to subtract fuel or enlean the mixture.

When Short FT is varying close to ±0%, this indicates a neutral condition where the basicinjection duration calculation is very close to stoichiometry, without any significant correction for02S.





How Long FT WorksLong FT is a data parameter on the OBD and OBD-II data streams. It is a more permanentcorrection to fuel delivery because it is part of the basic injection duration calculation. Long FT

changes slowly, in response to Short FT. Its normal range is ±20%, positive values indicatingrich correction and negative values indicating lean correction.

If Short FT deviates significantly from ±10% for too long, the Long FT shifts, changing the basicinjection duration. This shift in basic injection duration should bring Short FT back to the ±10%range.

Unlike Short FT which effects injection duration calculation in closed loop only, the Long FTcorrection factor effects the basic injection duration calculation in open and closed loop.Because Long FT is stored in a nonvolatile RAM (NVRAM) and is not erased when the ignitionis switched off, the fuel system is able to correct for variances in engine and fuel conditions

even during warm-up and wide open throttle conditions.

On OBD data streams, Long FT is displayed as Target A/F. On non data stream equippedengines, Long FT is referred to as Learned Voltage Feedback (LVF) and can be accessed fromthe check connector VF1 terminal.

To gain a better understanding of Long and Short fuel trim, use the example given below.Referring to the graphic on the opposite page:

Condition #1shows a fuel system operating within normal design parameters. Based on engine load and

speed, basic injection is calculated at 3.0 ins. The short FT is varying ±10% and oxygen sensorvoltage switching is normal.

Condition #2shows effects of air leak into intake. Basic injection remains at 3.0 ms because none of theinputs effecting basic injection duration have changed.

• Extra air causes engine to run lean, causing oxygen sensor to go lean.

• Short FT tries to correct but reaches +20% limit without bringing oxygen sensor back tonormal switching.

• ECM learns that it will need to increase basic injection duration so that oxygen sensorcan return to normal operating range.





Condition #3shows what happens after ECM shifts Long FT to +10%. Although MAF and rpm remain thesame, basic injection increases by 10% based on shift in Long FT. Basic injection is now

3.3 ms.

• The fuel system is now supplying enough fuel to restore nearly normal oxygen sensorswitching. Switching is taking place but the voltage swings are lower than normal. ShortFT is still making an excessive correction (+15%) to achieve this.

• ECM learns that it must continue shifting Long FT to get Short FT back to ±10%.

Condition #4shows the result of another shift in Long FT. MAF and rpm are still the same as in condition #1,however, basic injection duration has increased by 20% to 3.6 ms.

• Basic injection is now back within ±10% of required injection.

• Normal oxygen sensor switching is accompanied by Short FT switching ±10% of basicinjection duration.





Learned Voltage Feedback and Target Ai r Fuel RatioAlthough Long FT, Target A/F, and LVF (Learned Voltage Feedback) are essentially the same,there is a difference in how this data parameter is displayed on OBD engines. LVF and Target

A/F are displayed as a voltage signal with a range of 0 to 5 volts. The signal, which varies infixed 1.25 volt increments, has a nominal value of 2.50 volts.

When LVF is at 2.50 volts, it indicates that basic injection duration calculation is within ±10% of required injection duration (to achieve 14.7 to 1 AFR). If basic injection duration deviates morethan ±10% of required injection, LVF will shift to correct the excessively lean or rich condition.

Lower voltage indicates decreased injection duration to correct for a rich condition. Highervoltage indicates increased injection duration to correct for a lean condition.





Using Fuel Trim in DiagnosisWhen troubleshooting driveability problems, one of the first checks to make is a quickinspection of the oxygen feedback system. Determine if the vehicle is operating in closed loop

and if the fuel system is correcting for an excessively lean or rich operating condition.

When to Use Fuel Trim DataFuel trim value outside of prescribed operating range is not a problem in itself. This condition istypically an indication that other problems exist. Fuel trim data can help lead you to the causeof these problems. Typically you will use fuel trim data to:

• Perform a pre-diagnosis quick check of feedback control• Troubleshoot the cause of emissions system failure (I/M test failures)• Troubleshoot cause of driveability problems, particularly when these problems occur

during open loop operating modes (i.e. starting, warm-up, power enrichment)• Perform post-repair quick check of feedback control

Where to Find Fuel Trim Data The easiest way to perform a fuel trim inspection is to use your Diagnostic Tester. Fuel trimdata is available on all OBD-II and most OBD data streams. The following chart indicateswhat fuel trim data is available for diagnosis:





How to Determine Fuel System Loop StatusLong FT and LVF only "learns" during closed loop operation. Therefore, the engine must beoperating in closed loop when performing tests involving fuel trim data. To confirm closed loop

operation, refer to the following chart:

An alternate method of determining closed loop operation on all vehicles with DLC 1 (CheckConnector) is to use your Diagnostic Tester to perform the 02S/rpm test. This test allows you tomonitor the oxygen sensor(s) signal frequency and amplitude directly from the OX1 and OX2terminals of DLC 1.





Sub-systems and Conditions Affecting Fuel TrimOnce you know the driveability symptom and are able to confirm that the air/fuel ratio isexcessively lean or rich, it is a fairly easy task to identify all of the sub-systems which can effect

the mixture. Check each sub-system to confirm proper operation.

The following chart lists sub-systems and other factors which can cause the oxygen feedbacksystem to make rich or lean corrections and, in some cases, cause fuel trim data to approachits correction limits:

NOTE: OBD vehicles without High Altitude Compensation operating at high altitude (> 5000feet) may operate at the lean fuel trim correction limit. This is a normal condition.





Introduction to Combustion Chemistry The gasoline-powered internal combustion engine takes air from the atmosphere andgasoline, a hydrocarbon fuel, and through the process of combustion releases the chemical

energy stored in the fuel. Of the total energy released by the combustion process, about 20% isused to propel the vehicle, the remaining 80% is lost to friction, aerodynamic drag, accessoryoperation, or simply wasted as heat transferred to the cooling system.

Modern gasoline engines are very efficient compared to predecessors of the late '60s and early'70s when emissions control and fuel economy were first becoming a major concern of automotive engineers. Generally speaking, the more efficient an engine becomes, the lower theexhaust emissions from the tailpipe. However, as clean as engines operate today, exhaustemission standards continually tighten. The technology to achieve these ever-tighteningemissions targets has led to the advanced closed loop engine control systems used on today's Toyota vehicles. With these advances in technology comes the increased emphasis on

maintenance, and when the engine and emission control systems fail to operate as designed,diagnosis and repair.

Understanding the Combustion Process To understand how to diagnose and repair the emissions control system, one must first have aworking knowledge of the basic combustion chemistry which takes place within the engine. That is the purpose of this section of the program.

The gasoline burned in an engine contains many chemicals, however, it is primarily made up of hydrocarbons (also referred to as HC. Hydrocarbons are chemical compounds made up of hydrogen atoms which chemically bond with carbon atoms. There are many different types of

hydrocarbon compounds found in gasoline, depending on the number of hydrogen and carbonatoms present, and the way that these atoms are bonded.

Inside an engine, the hydrocarbons in gasoline will not burn unless they are mixed with air. This is where the chemistry of combustion begins. Air is composed of approximately 21%oxygen (02), 78% nitrogen (N2), and minute amounts of other inert gasses.

EMISSIONS #1 - COMBUSTION CHEMISTRY




The hydrocarbons in fuel normally react only with the oxygen during the combustion process toform water vapor (H2O) and carbon dioxide (CO2), creating the desirable effect of heat andpressure within the cylinder. Unfortunately, under certain engine operating conditions, the

nitrogen also reacts with the oxygen to form nitrogen oxides (NOx), a criteria air pollutant.

The ratio of air to fuel plays an important role in the efficiency of the combustion process. Theideal air/fuel ratio for optimum emissions, fuel economy, and good engine performance isaround 14.7 pounds of air for every one pound of fuel. This "ideal air/fuel ratio" is referred to asstoichiometry, and is the target that the feedback fuel control system constantly shoots for. Atair/fuel ratios richer than stoichiometry, fuel economy and emissions will suffer. At air/fuel ratiosleaner than stoichiometry, power, driveability and emissions will suffer.





Under "Ideal" Combustion Conditions

In a perfectly operating engine with ideal combustion conditions, the following chemicalreaction would take place:

• Hydrocarbons would react with oxygen to produce water vapor (H2O) and carbon dioxide(CO2)

• Nitrogen (N2) would pass through the engine without being affected by the combustion process.

In essence, only harmless elements would remain and enter the atmosphere. Althoughmodern engines are producing much lower emission levels than their predecessors, they stillinherently produce some level of harmful emission output.

The Four-Stroke Combustion CycleDuring the Intake Stroke, air and fuel moves into the low pressure area created by the piston

moving down inside the cylinder. The fuel injection system has calculated and delivered theprecise amount of fuel to the cylinder to achieve a 14.7 to 1 ratio with the air entering thecylinder.

As the piston moves upward during the Compression Stroke, a rapid pressure increaseoccurs inside the cylinder, causing the air/fuel mixture to superheat. During this time, theantiknock property or octane rating of the fuel is critical in preventing the fuel from ignitingspontaneously (exploding). This precise superheated mixture is now prime for ignition as thepiston approaches Top Dead Center.





J ust before the piston reaches top dead center to start the Power Stroke, the spark plug ignitesthe air/fuel mixture in the combustion chamber, causing a flame-front to begin to spreadthrough the mixture. During combustion, hydrocarbons and oxygen react, creating heat and

pressure. Ideally, the maximum pressure is created as the piston is about 8 to 12 degrees pasttop dead center to produce the most force on the top of the piston and transmit the most powerthrough the crankshaft. Combustion by-products will consist primarily of water vapor andcarbon dioxide if the mixture and spark timing are precise.

After the mixture has burned and the piston reaches bottom dead center, the Exhaust Strokebegins as the exhaust valve opens and the piston begins its return to top dead center. Thewater vapor, carbon dioxide, nitrogen, and a certain amount of unwanted pollutants are pushedout of the cylinder into the exhaust system.





Harmful Exhaust EmissionsAs previously mentioned, even the most modern, technologically advanced automobile enginesare not "perfect"; they still inherently produce some level of harmful emission output. There are

several conditions in the combustion chamber which prevent perfect combustion and causeunwanted chemical reactions to occur. The following are examples of harmful exhaustemissions and their causes.

Hydrocarbon (HC) EmissionHydrocarbons are, quite simply, raw unburned fuel. When combustion does not take place atall, as with a misfire, large amounts of hydrocarbons are emitted from the combustionchamber.

A small amount of hydrocarbon is created by a gasoline engine due to its design. A normalprocess called wall quenching occurs as the combustion flame front burns to the relatively coolwalls of the combustion chamber. This cooling extinguishes the flame before all of the fuel isfully burned, leaving a small amount of hydrocarbon to be pushed out the exhaust valve.





Another cause of excessive hydrocarbon emissions is related to combustion chamberdeposits. Because these carbon deposits are porous, hydrocarbon is forced into these poresas the air/fuel mixture is compressed. When combustion takes place, this fuel does not burn,

however, as the piston begins its exhaust stroke, these hydrocarbons are released into theexhaust stream.

The most common cause of excessive hydrocarbon emissions is misfire which occurs due toignition, fuel delivery, or air induction problems. Depending on how severe the misfire,inadequate spark or a noncombustible mixture (either too rich or too lean) will causehydrocarbons to increase to varying degrees. For example, a total misfire due to a shortedspark plug wire will cause hydrocarbons to increase dramatically. Conversely, a slight leanmisfire due to a false air entering the engine, may cause hydrocarbons to increase only slightly.

Excess hydrocarbon can also be influenced by the temperature of the air/ fuel mixture as it

enters the combustion chamber. Excessively low intake air temperatures can cause poormixing of fuel and air, resulting in partial misfire.





Carbon Monoxide (CO) EmissionCarbon monoxide (CO) is a byproduct of incomplete combustion and is essentially partiallyburned fuel. If the air/fuel mixture does not have enough oxygen present during combustion, it

will not bum completely. When combustion takes place in an oxygen starved environment, thereis insufficient oxygen present to fully oxidize the carbon atoms into carbon dioxide (CO2). Whencarbon atoms bond with only one oxygen atom carbon monoxide (CO) forms.

An oxygen starved combustion environment occurs as a result of air/fuel ratios which are richerthan stoichiometry (14.7 to 1). There are several engine operating conditions when this occursnormally. For example, during cold operation, warm-up, and power enrichment. It is, therefore,normal for higher concentrations of carbon monoxide to be produced under these operatingconditions. Causes of excessive carbon monoxide includes leaky injectors, high fuel pressure,

improper closed loop control, etc.





When the engine is at warm idle or cruise, very little carbon monoxide is produced becausethere is sufficient oxygen available during combustion to fully oxidize the carbon atoms. Thisresults in higher levels of carbon dioxide (CO2) the principal by-product of efficient combustion.

Oxides of Nitrogen (NOx) EmissionHigh cylinder temperature and pressure which occur during the combustion process can causenitrogen to react with oxygen to form Oxides of Nitrogen (NOx). Although there are various formsof nitrogen-based emissions that comprise Oxides of Nitrogen (NOx), nitric oxide (NO) makesup the majority, about 98% of all NOx emissions produced by the engine.

Generally speaking, the largest amount of NOx is produced during moderate to heavy loadconditions when combustion pressures and temperatures are their highest. However, smallamounts of NOx can also be produced during cruise and light load, light throttle operation.Common causes of excessive NOx include faulty EGR system operation, lean air/fuel mixture,high temperature intake air, overheated engine, excessive spark advance, etc.





Air/Fuel Mixture Impact on Exhaust EmissionsAs you can see in the graph above, HC and CO levels are relatively low near the theoreticallyideal 14.7 to 1 air/fuel ratio. This reinforces the need to maintain strict air/fuel mixture control.However, NOx production is very high just slightly leaner than this ideal mixture range. Thisinverse relationship between HC/CO production and NOx production poses a problem whencontrolling total emission output. Because of this relationship, you can understand the

complexity in reducing all three emissions at the same time.





Exhaust Analysis Using 4 and 5 Gas AnalyzersSo far we've discussed how harmful exhaust emissions are produced during combustion.However, in addition to these harmful emissions, both carbon dioxide (CO2) and oxygen (O2)

readings can provide additional information on what's going on inside the combustionchamber.

Carbon Dioxide (CO2)Carbon dioxide, or CO2, is a desirable byproduct that is produced when the carbon from thefuel is fully oxidized during the combustion process. As a general rule, the higher the carbondioxide reading, the more efficient the engine is operating. Therefore, air/fuel imbalances,misfires, or engine mechanical problems will cause CO2 to decrease. Remember, "ideal"combustion produces large amounts Of CO2 and H2O (water vapor).

EMISSIONS #2 - EMISSION ANALYSIS




Oxygen (O2)Oxygen (O2) readings provide a good indication of a lean running engine, since O2 increaseswith leaner air/fuel mixtures. Generally speaking, O2 is the opposite of CO, that is, O2 indicates

leaner air/fuel mixtures while CO indicates richer air/fuel mixtures. Lean air/fuel mixtures andmisfires typically cause high O2 output from the engine.

Other Exhaust Emissions There are a few other exhaust components which impact driveability and/or emissionsdiagnosis, that are not measured by shop analyzers. They are:

• Water vapor (H2O)• Sulfur Dioxide (SO2)• Hydrogen (HO• Particulate carbon soot (C)

Sulfur dioxide (SO2) is sometimes created during the combustion process from the smallamount of sulfur present in gasoline. During certain conditions the catalyst oxidizes sulfur

dioxide to make SO3, which then reacts with water to make H2SO4 or sulfuric acid. Finally,when sulfur and hydrogen react, it forms hydrogen sulfide gas. This process creates the rottenegg odor you sometimes smell when following vehicles on the highway. Particulate carbonsoot is the visible black "smoke you see from the tailpipe of a vehicle that's running very rich.





Causes of Excessive Exhaust Emissions As a general rule, excessive HC, CO, and NOx levels are most often caused by the followingconditions:

• Excessive HC results from ignition misfire or misfire due to excessively lean or richair/fuel mixtures

• Excessive CO results from rich air/fuel mixtures• Excessive NOx results from excessive combustion temperatures

There are lesser known causes to each of these emissions that will be discussed later. Whentroubleshooting these types of emissions failures, you will be focusing on identifying the causeof the conditions described above. For example, to troubleshoot the cause of excessive COemissions, you need to check all possible causes of too much fuel or too little air (rich airfuel/ratio). The following lists of causes will help familiarize you with the sub-systems most

often related to excessive CO, HC and NOx production.

Causes of Excessive HydrocarbonsAs mentioned, high hydrocarbons is most commonly caused by engine misfires. The followinglist of problems could cause high HC levels on fuel injected vehicles. As with any quickreference, there are other less likely causes that may not be included in the list. Here are someof the more common causes:

• Ignition system failures-faulty ignition secondary component-faulty individual primary circuit on distributorless ignition system

-weak coil output due to coil or primary circuit problem• Excessively lean air/fuel mixture

- leaky intake manifold gasket- worn throttle shaft

• Excessive EGR dilution- EGR valve stuck open or excessive EGR flow rate- EGR modulator bleed plugged

• Restricted or plugged fuel injector(s)

• Closed loop control system incorrectly shifted lean

• False input signal to ECM-incorrect indication of load, coolant temp., O2 content, or throttle position

• Exhaust leakage past exhaust valve(s)- tight valve clearances- burned valve or seat

• Incorrect spark timing- incorrect initial timing- false input signal to ECM





• Excessive combustion blowby- worn piston rings or cylinder walls

• Insufficient cylinder compression

• Carbon deposits on intake valves

Causes of Excessive Carbon MonoxideHigh carbon monoxide levels are caused by anything that can make the air/mixture richer than"ideal". The following examples are typical causes of rich mixtures on fuel injected vehicles:

• Excessive fuel pressure at the injector(s)

• Leaking fuel injector(s)

• Ruptured fuel pressure regulator diaphragm

• Loaded/malfunctioning EVAP system (two speed idle test)

• Crankcase fuel contamination (two speed idle test)

• Plugged PCV valve or hose (two speed idle test)

• Closed loop control system incorrectly shifted rich

• False input signal to ECM-incorrect indication of load, coolant temp., O2 content, or throttle position

Note: It should be pointed out that due to the reduction ability of the catalytic converter,increases in CO emissions tend to reduce NOx emissions. It is not uncommon to repair a COemissions failure and, as a result of another sub-system deficiency, have NOx increasesufficiently to fail a loaded-mode transient test.





Causes of Excessive Oxides of NitrogenExcessive oxides of nitrogen can be caused by anything that makes combustion temperaturesrise. Typical causes of high combustion temperature on fuel injected vehicles include:

• Cooling system problems- insufficient radiator airflow- low coolant level- poor cooling fan operation- thermostat stuck closed or restricted- internal radiator restriction

• Excessively lean air/fuel mixture- leaky intake manifold gasket- worn throttle shaft

• Closed loop control system incorrectly shifted lean

• Improper oxygen sensor operation- slow rich to lean switch time- rich biased 02 sensor voltage

• Improper or inefficient operation of EGR system- restricted EGR passage- EGR valve inoperative- EGR modulator inoperative

- plugged E or R port in throttle body- faulty EGR VSV operation- leaky/misrouted EGR hoses

• Improper spark advance system operation- incorrect base timing- false signal input to ECM- improper operation of knock retard system

• Carbon deposits on intake valves





Evaporative Emissions

Up to now, we've only discussed the creation and causes of tailpipe or exhaust emissionoutput. However, it should be noted that hydrocarbon (HC) emissions come from the tailpipe,as well as other evaporative sources, like the crankcase, fuel tank and evaporative emissionsrecovery system.

In fact, studies indicate that as much as 20% of all HC emissions from automobiles comesfrom the fuel tank and carburetor (on carbureted vehicle, of course). Because hydrocarbonemissions are Volatile Organic Compounds (VOCs) which contribute to smog production, it is just as important that evaporative emission controls are in as good a working order ascombustion emission controls.

Fuel injected vehicles use an evaporative emissions system to store fuel vapors from the fueltank and burn them in the engine when it is running. When this system is in good operatingorder, fuel vapor cannot escape from the vehicle unless the fuel cap is removed. The subject of Evaporative Emissions Systems is addressed in the next section of this program.





Diagnosis Using an Exhaust Gas Analyzer Use of a four or five gas exhaust analyzer can be helpful in troubleshooting both emissions anddriveability concerns. Presently, shop grade analyzers are capable of measuring from as few astwo exhaust gasses, HC and CO, to as many as five. The five gasses measured by the latesttechnology exhaust analyzers are: HC, CO, CO2, O2 and NOx. Remember, HC, CO, CO2, andNOx are measured in Enhanced I/M programs.

All five of these gasses, especially O2 and CO2, are excellent troubleshooting tools. Use of anexhaust gas analyzer will allow you to narrow down the potential cause of driveability and

emissions concerns, focus your troubleshooting tests in the area(s) most likely to be causingthe concern, and save diagnostic time. In addition to helping you focus your troubleshooting, anexhaust gas analyzer also gives you the ability to measure the effectiveness of repairs bycomparing before and after exhaust readings.

In troubleshooting, always remember the combustion chemistry equation: Fuel (hydrogen,carbon, sulfur) + Air (nitrogen, oxygen) = Carbon dioxide + water vapor + oxygen + carbonmonoxide + hydrocarbon + oxides of nitrogen + sulfur oxides

In any diagnosis of emission or driveability related concern, ask yourself the followingquestions:

• What is the symptom?

• What are the "baseline" exhaust readings? At idle, 2500 rpm, acceleration, deceleration,light load cruise, etc.

• Which sub-system(s) or component(s) could cause the combination of exhaust gasreadings measured?





The Effects of Secondary Air Some Toyota engines use a secondary air system to supplement the oxygen supply for theoxidation catalyst. This supplementary air is introduced into the exhaust stream upstream of the

catalytic converter. Secondary air increases the oxygen content of the exhaust stream andreduces the carbon dioxide by diluting it.

Analyzing Exhaust Emission Readings

• Hydrocarbons are measured by an exhaust analyzer in parts per million (ppm). As youknow, HC is unburned fuel that remains as a result of a misfire. When combustiondoesn't take place or when only part of the air/fuel charge burns, hydrocarbon levelsgoes up.

• Carbon Monoxide is measured by an exhaust analyzer in percent (%) or parts perhundred. CO is a byproduct of combustion, therefore, if combustion does not take place,carbon monoxide will not be created. Based on this premise, when a misfire occurs, thecarbon monoxide that would have normally been produced during the productionprocess is not produced. Generally speaking, on fuel injected vehicles, high CO meanstoo much fuel is being delivered to the engine for the amount of air entering the intakemanifold.

• Nitrogen Oxides measured by an exhaust analyzer in parts per million (ppm). Nitrogenoxides are a by-product of combustion. NOx is formed in large quantities when

combustion temperatures exceed about 2500' F. Anything which causes combustiontemperatures to rise will also cause NOx emissions to rise. Misfire can also cause NOxto rise because of the increase in oxygen that it causes in the catalytic converter feedgas.

• Carbon Dioxide measured by an exhaust analyzer in percent (%) or parts per hundred.Carbon dioxide is a by-product of efficient and complete combustion. Near perfectcombustion will result in carbon dioxide levels which approach the theoretical maximumof 15.5%. Carbon dioxide levels are effected by air/fuel ratio, spark timing, and any otherfactors which effect combustion efficiency.





• Oxygen is measured by an exhaust analyzer in percent (%) or parts per hundred. Theamount of oxygen produced by an engine is effected by how close the air/fuel ratio is tostoichiometry. As the mixture goes lean of stoichiometry, oxygen increases. As mixture

goes rich of stoichiometry, oxygen falls close to zero. Because oxygen is used up in thecombustion process, concentrations at the tailpipe will be very low. If misfire occurs,however, oxygen will increase dramatically as it passes unused through the combustionchamber.

Another factor in analyzing NOx emissions are the two primary emissions sub-systemsdesigned to control NOx levels, the EGR and reduction catalyst systems. NOx emissions willincrease when the EGR system malfunctions or when the reduction catalyst efficiency falls.Efficiency of the reduction catalyst is closely tied to normal operation of the closed loop fuelcontrol system. Reduction efficiency falls dramatically when catalyst feed gas carbon monoxidecontent is too low (oxygen content too high.)





Pre-Catalyst Versus Post-Catalyst TestingWhen using an exhaust analyzer as a diagnostic tool, it is important to remember thatcombustion takes place twice before reaching the tailpipe. First, primary combustion takes

place in the engine. This determines the composition of catalyst feed gas, which dramaticallyeffects catalyst efficiency. When the exhaust gases reach the three-way catalytic converter, twochemical processes occur.

Catalyst ReductionFirst, nitrogen oxide gives up its oxygen. This only occurs when a sufficient amount of carbonmonoxide is available for the oxygen to bond with. This chemical reaction results in reduction of nitrogen oxide to pure nitrogen and oxidation of the carbon monoxide to form carbon dioxide.

Catalyst OxidationSecond, hydrocarbon and carbon monoxide continue to burn. This occurs only if there asufficient amount of oxygen available for the hydrogen and carbon to bond with. This chemicalreaction results in oxidation of hydrogen and carbon to form water vapor (H2O) and carbondioxide (CO2).





Examples of Deceiving Post-Catalytic AnalysisWhen troubleshooting an emissions failure, your primary concern will be what comes out of thetailpipe. In other words, it doesn't matter whether the efficient burn occurred in the engine or the

catalyst. However, when troubleshooting a driveability concern, the catalytic converter may maskimportant diagnostic clues which can be gathered with your exhaust analyzer. The following areexamples of situations where post-catalyst reading may be deceiving.

• Example 1: A minor misfire under load is causing a vehicle to surge. The exhaust gasfrom the engine would show an increase in HC and O2, and a reduction in CO2.However, once this exhaust gas reaches the catalytic converter, especially a relativelynew and efficient catalyst, the oxidation process will continue. The excess HC will beoxidized, causing HC and O2 to fall, and CO2 to increase. At the tailpipe, the exhaustreadings may look perfectly normal.

In this example, it is interesting to note that NOx readings will increase because of the

reduced carbon monoxide and increased oxygen levels in the catalyst feed gas. Thiscould be detected with a five gas analyzer.





• Example 2: A small exhaust leak upstream of the exhaust oxygen sensor is causing afalse lean indication to the ECM. This resulted in excessively rich fuel delivery to bringoxygen sensor voltage back to normal operating range. The customer concern is a

sudden decrease of 20% in fuel economy.

• Example 3: A restriction in the fuel return line elevates pressure causing an excessivelyrich air/fuel ratio and a 20% decrease in fuel economy. Although carbon monoxideemissions from the engine are elevated as a result of this rich air/fuel ratio, the catalyticconverter is able to oxidize most of it into carbon dioxide. The resulting tailpipe readingsappear to be normal, except for oxygen, which is extremely low for two reasons. First, theincrease in CO caused a proportionate decrease in O2 in the converter feed gas.Second, the little oxygen left over was totally consumed oxidizing the CO into CO2.

Based on this example, you can see that oxygen is a better indicator of lean or richair/fuel ratios than carbon monoxide when testing post catalytic converter.





General Rules of Emission Analysis• If CO goes up, O2 goes down, and conversely if O2 goes UP, CO goes down.

Remember, CO readings are an indicator of a rich running engine and O2 readings arean indicator of a lean running engine.

• If HC increases as a result of a lean misfire, O2 will also increase

• CO2 will decrease in any of the above cases because of an air/fuel imbalance or misfire

• An increase in CO does not necessarily mean there will be an increase in HC. AdditionalHC will only be created at the point where rich misfire begins (3% to 4% CO)

• High HC, low CO, and high O2 at same time indicates a misfire due to lean or EGRdiluted mixture

• High HC, high CO, and high O2 at same time indicates a misfire due to excessively richmixture.

• High HC, Normal to marginally low CO, high O2, indicates a misfire due to a mechanicalengine problem or ignition misfire

• Normal to marginally high HC, Normal to marginally low CO, and high O2 indicates amisfire due to false air or marginally lean mixture





To verify that the exhaust readings are not being diluted in the exhaust system or analyzersampling point, combine the CO reading with the CO2 reading. An undiluted sample shouldalways have a sum of greater than 6%. Remember, the secondary air system may be diluting

the sample if it is not disabled during analysis. In fact, engines with secondary air injectionsystems will have relatively high oxygen concentrations in the exhaust because of the extra airpumped into the exhaust, post combustion.

Factors That Degrade Emissions & Driveability The following major factors contribute to the overall increase in exhaust emissions levels anddegraded vehicle driveability:

• Lack of scheduled maintenance- Sub-system failures- Combination of multiple marginal sub-systems

• Tampering- Removal of emissions sub-system equipment- Modification of engine/emissions sub-systems

• Use of leaded fuels or incompatible additives in closed loop control systems





Engine Mechanical The engine control and emissions sub-systems all rely on good mechanical condition of theengine to operate normally and effectively. Mechanical malfunctions effect exhaust emissions

and driveability, both directly and indirectly:

• Directly, any mechanical malfunction will likely cause significant increases in exhaustemissions by causing misfire, allowing combustion gasses to escape past exhaustvalves or piston rings, by altering air/fuel ratios, or any number of other possibilities.

• Indirectly, mechanical malfunctions change the composition of catalyst feed gas,preventing the catalytic converter from operating efficiently.

Examples of mechanical problems that can increase exhaust emission output include; lowcylinder compression causing poor combustion and/or misfire, worn oil control rings that allow

excessive engine oil (HC) to be consumed during combustion, etc. Remember, always checkthe integrity of basic engine mechanical systems before moving on to more complex engine oremission sub-systems.

Air Induction System The air induction sub-system meters and measures engine air based on driver demand. In theevent that unmetered air enters the engine or if it is not measured accurately, the unbalancedair /fuel ratio will cause increases in exhaust emissions and/or driveability concerns. Thefollowing areas of the air induction system may require your attention when troubleshooting anemissions or driveability concern.

EMISSION SUB SYSTEMS - Eng ine & Emis s io n System s




False Intake Air EntryIf unmeasured air enters engines equipped with L-type injection, they may exhibit lean surges,misfire and rough idle. Lean operating conditions can also cause increases in hydrocarbons,

due to misfire, and in NOx due to leaner air/fuel ratios, increased combustion temperatures anddecreased reduction catalyst efficiency.

Engines equipped with D-type injection will exhibit an elevated engine idle speed if

unmeasured air enters the induction system. Generally, this will not cause exhaust emissionsto increase significantly.

Intake Valve Deposi tsIntake valve deposits are hardened carbon deposits which form on the back side of the intakevalve. The degree of deposits vary depending on many factors like fuel properties, drivinghabits, and engine family. Intake valve deposits can cause driveability concerns as well asincreased exhaust emissions.

Excessive intake valve deposits can cause an engine to run excessively lean while cruising andaccelerating, and excessively rich during deceleration. During lean operating periods, NOx

emissions are elevated. During rich operating periods, CO emissions are elevated. Theamount of emissions increase has a linear relationship with the degree of deposits on thevalves. At some point, deposits can effect emissions enough to put a vehicle out of compliancein an Enhanced I/M test.





Effects of Intake Valve Deposits on Driveabilit y There are several common driveability symptoms which can be caused by intake valvedeposits; stumble, hesitation and loss of power under load. Stumble and hesitation, especiallywhen the engine is cold, are by far the most common problems caused by excessive intakevalve deposits. The porous carbon deposits act like a sponge, absorbing enough fuel vapor tocause these symptoms.

Severe carbon deposits can also cause a loss of power at high engine rpm. When depositsaccumulate sufficiently to restrict airflow through the intake valve, the volumetric efficiency of theengine is effected, causing the engine to loose power.

The best way to confirm excessive deposits is to visually inspect the valves using a borescope.If repairs are necessary, equipment is available to clean the valves without removing thecylinder head. Refer to Toyota Technical Service Bulletins for more information on procedures

and special service tools.





Fuel Delivery System The fuel delivery and injection control system delivers fuel to the engine and meters the amountof fuel which is injected into the intake manifold. There are two factors which, under normalconditions, should determine the air/fuel ratio; fuel pressure and in jection duration. In theevent that either of these factors is incorrect, normal air/fuel ratio will be upset.

One factor which can upset the normal air/fuel ratio is unmeasured fuel. Leaking injectors, aleaking fuel pressure regulator diaphragm, crankcase oil diluted with gasoline, or a saturatedevaporative emissions system can all cause an excessively rich air/fuel ratio.

Finally, the air fuel ratio can also be upset by restriction in the injector nozzle or problems withthe injector spray pattern. Symptoms caused by fuel injector spray pattern and restrictions aresimilar to those caused by intake valve deposits; stumble, hesitation, loss of power, etc.





Fuel Injector Test Methods Testing fuel injectors for restriction and/or spray pattern can be accomplished one of two ways;visual inspection and pressure drop method.

Visual InspectionVisual inspection requires that the suspect injector(s) be removed from the engine, connectedto a test apparatus, and electrically energized for a fixed time period. The injector should deliverthe specified volume and spray pattern should appear uniformly conical.

Pressure Drop Test The pressure drop method requires the use of a fuel pressure gauge and an injector pulsetimer available from specialty tool vendors. Generally speaking, this test can be performedwithout removing the injector from the engine. By energizing the injector for a fixed pulse widthand observing the pressure drop on the fuel system, the relative fuel flow can be compared foreach injector. If all injectors exhibit a consistent pressure drop, it follows that all injectors areflowing the same volume of fuel. There are three shortcomings with this type of test which limitits usefulness, they are:

• Actual injector flow volume can not be determined, only relative flow

• Spray pattern cannot be observed during this test

• There are no specifications for the pressure drop test.





Incorrect Injection DurationIn addition to the problems mentioned above, false sensor input from any of the six major inputsensors can also cause the air/fuel ratio to shift sufficiently to cause driveability and/or

emissions concerns. If engine load is incorrectly calculated, fuel requirements are alsomiscalculated, resulting in a driveability or emissions concern. This type of a condition can beidentified by reading sensor signals and comparing them to standard values. With this type of condition, the ECM adaptive fuel program will probably be making major corrections to bring theair/fuel ratio back into a neutral range (stoichiometry).

The best way to confirm that a neutral air/fuel ratio is being delivered to the engine, is to monitorthe adaptive fuel correction to injection duration. This can be accomplished several differentways, depending on the engine being tested:

1. OBD vehicles without serial data: Use a voltmeter on terminal VF1 at DLC 1 (checkconnector)

2. OBD vehicles with serial data: Use a scan tool to monitor Target A/F data

3. OBD-II vehicles: Use a scan tool to monitor Fuel Trim data





A Few Words on FuelEffects of Octane Rating on Engine Performance and "Knocking"When diagnosing any customer concern related to poor engine performance or engine

"knocking", always suspect fuel quality, or more specifically the octane rating of the fuel beingused. The octane rating is a reflection of the fuel's ability to withstand engine knock, and is ratedby its Antiknock Index (or pump octane rating). This number is displayed on a yellow sticker onthe side of each gas pump.

Since octane requirements differ from vehicle to vehicle, always check in the Owner's Manualfor vehicle's exact octane requirement and verify with the customer that their concern is not theresult of low octane fuel. On vehicles with Knock Control systems, low octane may not causethe engine to knock, since the system has the ability to retarded spark advance; however, theengine may perform poorly as a result of a conservative spark advance strategy. If the engineknocking or performance concern is not the result of a sub-system problem, you may want to

suggest to the customer a change in fuel grade or retailer.

Gasoline Volatil ity and Seasonal Fuel BlendsVolatility refers to a fuel's ability to change from a liquid to a vapor. This characteristic of fuel isvery important in maintaining satisfactory vehicle driveability. If fuel volatility is too low, hardstarting and poor warm-up driveability problems may result. If fuel volatility is too high, vaporlock, hot driveability problems, and excessive evaporative emissions may result.

Since fuel vaporization is naturally sensitive to ambient temperature change, refiners typicallyprovide a more volatile fuel blend in the winter to provide easy start-up and cold weatherdriveability. Conversely, in the summer, a less volatile fuel blend is provided to lessen the

chance of vapor lock or hot driveability problems.

Occasional driveability concerns may arise when retailers change blends between seasons(typically spring or fall). For example, if a change was made to a winter blend, yet the weatherremained uncharacteristically hot, a hot driveability problem may arise (and vice versa).

Oxygenated FuelsAs a result of the 1990 Clean Air Act Amendments, the use of oxygenated and reformulatedfuels has already occurred in many metropolitan areas across the United States. Oxygenatedgasoline contain oxygen carrying compounds (usually ethanol or MTBE) that chemicallyenleans the AT mixture. This leaner AT mixture results in lower carbon monoxide (CO)

emissions from the tailpipe.

A few points require clarification concerning oxygenated fuels. First, late model feedback controlvehicles may see a slight fuel economy loss (around 2%) when using oxygenated fuels. Thisoccurs as a result of feedback system enrichening the mixture when the O2 sensor detects theadditional oxygen provided by the fuel. Second, fuel system components in older modelvehicles may experience swelling (hoses, O-rings, gaskets, etc.) from the alcohol used insome oxygenated fuels. The Owner's Manual contains detailed information on the allowablepercentages of both MTBE and ethanol.





Emission Control Sub-Systems

Closed Loop Feedback Control System The heart of the emissions control system is the closed loop fuel feedback control system. It isresponsible for controlling the content of the catalytic converter feed gas and ultimatelydetermines how much HC, CO and NOx leaves the tailpipe. The closed loop control systemworks primarily during idle and cruise operations and makes adjustments to injection durationbased on signals from the exhaust oxygen sensor.

During closed loop operation, the ECM keeps the air/fuel mixture modulated around the ideal14.7 to 1 air/fuel ratio (stoichiometry). By precisely controlling fuel delivery, the oxygen content of the exhaust stream is held within a narrow range that supports efficient operation of the three-way catalytic converter. However, if the air/fuel ratio begins to deviate from its preprogrammedswings, catalyst efficiency falls dramatically, especially the reduction of NOx.

EMISSION SUB SYSTEMS - C losed Lo op Feedb ack Co nt ro l Sys tem




Closed Loop OperationWhen the ECM has determined conditions suitable for entering closed loop operation (basedon many sensor values), it uses the oxygen sensor signal to determine the exact concentrationof oxygen in the exhaust stream. From this signal, the ECM determines whether the mixture isricher (low 02) or leaner (high 02) than the ideal 14.7 to I air/fuel ratio:

• If the oxygen sensor signal is above 0.45 volt, the ECM determines that the air/fuelmixture is richer than ideal and decreases the injection duration.

• If the oxygen sensor signal is below 0.45 volt, the ECM determines that the air/fuelmixture is leaner than ideal and increases the injection duration.

During normal closed loop operation, the oxygen sensor signal switches rapidly between thesetwo conditions, at a rate of more than 8 cycles in 10 seconds at 2500 rpm. Small injectioncorrections take place each time the signal switches above and below the 0.45 thresholdvoltage.





Closed loop control works on the premise of the command changing the condition and can besummarized as follows:

• 02S indicates rich = ECM commands leaner injection duration

• 02S indicates lean = ECM commands richer injection duration

In short, the oxygen sensor informs the ECM of needed adjustments to injector duration basedon exhaust conditions. After adjustments are made, the oxygen sensor monitors the correctionaccuracy and informs the ECM of additional adjustments. This monitor/command cycle occurscontinuously during closed loop operation in an effort to keep the air/fuel mixture modulatedaround the ideal ratio.





Open Loop Operating Conditions There are certain operating conditions that require the mixture to be richer or leaner than ideal.During these conditions the ECM ignores the oxygen sensor signal and controls fuel durationusing other sensor information. This operation, called Open Loop, typically occurs during

engine start "clock out", cold engine operation, acceleration, deceleration, moderate to heavyload conditions, and wide open throttle (WOT).

Effects of Incorrect Closed Loop Control on Emissions and DriveabilityGenerally, incorrect fuel control affects emissions and driveability as follows:

• Air/fuel ratio too rich may result in emissions failure for CO and HC, rich misfire, enginestalling, rough idle, hesitation, overheated converter, etc.

• Air/fuel mixture too lean may result in failure for HC and NOx, lean misfire, enginestalling, stumble, flat spot, hesitation, rough idle, poor acceleration, etc.





Closed Loop Control System Functional ChecksIf you suspect that the closed loop system is not properly controlling fuel delivery, one of the firstchecks you should perform is an Oxygen (02) Sensor signal check. Since the ECM relies on the

02S signal to fine tune injection duration during closed loop operation, an accurate check of the02S signal is crucial in diagnosing problems that you suspect are the result of improper closedloop control.

Remember, the engine (and engine control system) must meet certain conditions prior tochecking the 02S signal or your results may be inaccurate. This usually means that the engineand 02 sensor must reach operating temperature, the feedback system is in closed loop, andengine speed is maintained at a specified rpm. 02S signal checks can be performed onOBD/OBD-II vehicles by using the Diagnostic Tester. Older vehicles may require you tobackprobe the 02S signal wire using the Autoprobe or digital multimeter.

Oxygen Sensor (02S) Signal ChecksMonitoring oxygen sensor signal switching frequency and amplitude is the key to a quickfunctional test of the entire closed loop control subsystem. The check can be performed asfollows:

• Start engine and allow it reach operating temperature

• Make sure all accessories are off

• Run engine at 2500 rpm for at least two minutes to ensure 02 sensor is at normaloperating temperature

• 02S signal frequency should be at least eight cycles in ten seconds (0.8 hz) in order toensure efficient catalyst operation.

• Also, signal amplitude should consistently exceed 550 mv on the rich swing and fallbelow 400 mv on the lean swing. If the sensor is degraded, either signal frequency oramplitude or both will be effected.





02S Check Using AutoprobeIf the Autoprobe feature of the Diagnostic Tester is used, set up the oscilloscope to read the02S signal. Follow these steps:

• Calibrate the Autoprobe

• Set time to 1 sec/div (use 0.2 sec/div when measuring switch time)

• Set volts to 0.2 v/div

• Set trigger to automatic

• Use the single shot trigger to capture and freeze the signal

02S Check Using a Digital Multimeter If a digital multimeter (DMM) is used, like the Fluke 80 series, set up the meter as follows:

• DC volts• Select the MIN/MAX feature• Press the MIN/MAX button to toggle between maximum, minimum, and average signal

voltage

Tests can be performed by connecting your test instrument to the OX1 / OX2 terminal of DLC1,or by back probing directly at the oxygen sensor connector.

Many factors can contribute to the degradation of the oxygen sensor including age andcontamination. Since this topic relates closely with catalytic converter operation, it will bediscussed in detail later.





Closed Loop Control Quick CheckIf you suspect that the ECM is not responding correctly to the oxygen sensor signal, a quickcheck of the closed loop system can be made by artificially driving the system rich or lean and

observing the corresponding change in closed loop fuel control. This check can be performedas follows:

• Temporarily remove the fuel pressure regulator signal hose and plug it, to create a richcondition. The ECM should respond by commanding the injectors to lean the mixture.

• Temporarily create an intake manifold vacuum leak to make a lean condition. The ECMshould respond by commanding the injectors to enrich the mixture.

On vehicles with serial data, changes to 02S signal, fuel trim, and injection duration can beobserved using the Diagnostic Tester.

CAUTION: When performing this type of check, avoid prolonged mixture imbalances (both leanor rich) for any extended length of time, as this may cause the catalyst to overheat andpermanently damage the converter.





Closed loop control has the ability to provide approximately ±20% correction range from thebasic fuel calculation. This allows the system to easily compensate for small mixture

imbalances; however, major air/fuel imbalances (such as large vacuum leaks, leaky fuelpressure regulator, etc.) may push its correction abilities to the limit without bringing the air/fuelmixture back to the "ideal" ratio. If this occurs, whether the mixture is driven too rich or too lean,increased emission levels and driveability problems may result from the systems inability tocorrect for these problems.

Check For Major Fuel CorrectionA quick check of the adaptive fuel correction will show the ECM's intentions of correcting thiscondition. Depending on the model, this adaptive correction factor may be called VF Voltage, Target AN, or Long-Term Fuel Trim, and on serial data equipped vehicles may be checkedusing the Diagnostic Tester.





Spark Advance Control The Spark Advance Control system maximizes engine efficiency by continuously adjustingspark advance timing to deliver peak combustion pressures when the piston reaches about 10'

after TDC. Incorrect spark timing can have a significant effect on emission output and vehicledriveability. If ignition timing is excessively advanced during certain conditions, detonation willoccur resulting in increased HC and NOx levels. Since NOx production is most predominantunder loaded engine operating conditions, the spark advance system must ensure accurateignition timing during these conditions. If ignition timing is incorrectly retarded, only partialcombustion will take place resulting poor engine performance and increased emission levels.

Causes of Incorrect Spark TimingOn systems that use the ECM to compute ignition spark advance, there are only two conditionswhich are likely to cause spark timing to be incorrect; initial timing or a false input signal to theECM.

The first step in troubleshooting emissions and driveability concerns should always include aquick check of initial ignition timing. Any error in initial timing will be reflected throughout theentire spark advance curve.

If engine load is miscalculated because of incorrect input signals, spark advance angle willnot be appropriate for engine operating conditions. This will result in driveability and emissionproblems. Refer to course 850 for additional information on spark advance strategy.

ENGINE SUB SYSTEMS - Spark A dv ance Co nt ro l




The Effects of Fuel Octane Toyota engines equipped with a knock detection system are very sensitive to fuel octane levels.Motor fuels with low octane ratings will cause the engine to detonate, which will in turn, cause

the detonation retard system to retard timing. On some vehicles with advanced ECM operatingstrategies, an adaptive memory factor is used to track signals from the knock sensor. Whendetonation occurs frequently, the ECM relearns the basic spark advance curve, retarding sparkthroughout the entire engine operating range. This retarded spark curve will negatively effectengine performance and fuel economy under all driving conditions, even after a tank of higheroctane fuel is purchased. The retarded spark curve will remain stored in the ECM keep alivememory until the engine is operated for a substantial amount of time on the higher octane fuel,or until the "keep alive memory" is cleared by removing power from the BATT terminal.

Purpose of Spark Advance Control Systems The amount of spark advance needed by the engine varies depending on a number of different

operating conditions. Generally, spark advance follows the following strategy:

• spark advance increases with higher engine speeds for performance and fuel economy.

• spark advance needs to decrease under heavy load conditions to avoid detonation.

They are many variables the system must consider when determining the proper spark leadtime. Coolant temperature, fuel quality, and engine load are just a few of the many factors thatcan significantly impact ideal ignition time. The ECM determines proper spark timing byapplying various input signals against a preprogrammed spark advance strategy or "map".

Fuel injected Toyota vehicles use either a mechanical or electronic spark advance controlsystem. They are referred to as either conventional EFI ignition system (mechanical), VariableAdvance Spark Timing (VAST) or Electronic Spark Advance (ESA).





Effects of Spark Advance on Emissions and Driveability•Too much spark advance, particularly during high engine load conditions, increases the

likelihood of engine detonation and increases combustion temperature and pressure.

This results in an increase in HC and NOx output, decreased engine performance, andpossible permanent damage the engine.

•Too little spark advance causes only partial combustion of the air/ fuel charge, resultingin very poor engine performance and fuel economy. Partial combustion will also result inan increase in CO levels.

Functional TestingSpark advance problems can result from an incorrect initial timing setting or a problem withspark advance during operation. Before attempting to check spark advance during operatingconditions, the initial or "base" ignition timing setting should checked and adjusted.

This procedure varies between systems, but on TCCS equipped vehicles, it generally requires jumping terminals at an underhood check connector (DLC1) to default the TCCS system toinitial timing. After checking or adjusting initial timing, remove the test wire to inform the ECM toreestablish corrective control over timing. Refer to the Repair Manual for details on performingthis procedure.





Even with initial timing correct, it is still possible that the system is miscalculating ignitiontiming as a result of incorrect sensor inputs. For example, if an airflow meter indicates lightengine load, when in fact, the engine is experiencing high engine load, the ECM may incorrectly

respond by over advancing ignition timing to the point of causing detonation. Refer to course850 and 873 handbook for additional information on spark advance control strategy.

If inaccurate sensor inputs are suspected on earlier EFI and TCCS vehicles, it is recommendedthat you perform standard voltage checks of all major sensor inputs to the ECM. Comparethese readings to those listed on the standard voltage chart on the Repair Manual or readingsobtained from other known good vehicles. On OBD-II vehicles, you may observe ignition timing

and identify incorrect signal data using the Diagnostic Tester. Some of the more importantspark control parameters include engine speed, engine load, throttle angle, and coolanttemperature.

On early EFI vehicles, all spark advance is handled by mechanical means. This system uses acentrifugal advance mechanism to represent engine speed and vacuum advance mechanismto represent engine load. Resolving advance problems with this type system requiresinspecting governor weights, springs, pivots, signal rotor, vacuum diaphragm, vacuum signalsource, breaker plate, etc.





Knock Detection Control The KNK (knock) input signal is critical in the prevention of engine detonation. The ECM usesthe knock sensor(s) to determine when, and to what degree, engine detonation is occurring

and then retards ignition timing as needed. The spark advance program is designed to providethe maximum spark advance possible, while keeping the engine from producing an audible"ping". If problems occur with this input signal, detonation may result, producing significantlevels of HC and NOx emissions.

The ECM is designed to filter out KNK signal voltages that it considers are outside of the enginedetonation range. Thus, a check of a knock control system by tapping on the engine close to theknock sensor may produce an output signal, but will not cause spark timing to retard. A check of the KNK signal pattern using the Diagnostic Tester Oscilloscope or lab scope may provide youthe most diagnostic information.





Idle Air Control Systems The Idle Air Control (IAC) system is used to stabilize idle speed during cold engine and afterwarm-up operations. Idle speed stabilization is needed due to the effect engine load changes

has on emission output, idle quality and vehicle driveability. The IAC system uses an ECMcontrolled idle air control valve (IACV) that regulates the volume of air bypassed around theclosed throttle. The ECM controls the IACV by applying various input signals against an IACprogram stored in memory.

There are four different types of IACVs used on Toyota models. These systems are referred toas:

• Step-Motor• Duty-Control Rotary Solenoid• Duty-Control Air Control Valve (ACV)• On/Off Vacuum Switching Valve (VSV)

Step-Motor IAC System This system uses a step-motor type IACV to control bypass airflow. The IACV consists of a step-motor with four coils, magnetic rotor, valve and seat, and can vary bypass airflow by positioningit's valve into one of 125 possible "steps". Basically, the higher the IACV step number, the largerthe airflow opening and the greater the volume of air bypassed around the closed throttle.

The ECM controls IACV positioning by sequentially energizing its four motor coils. For each coilthat is pulsed, the IACVs magnetic rotor moves one step, which in turn changes the valve andseat positioning slightly. The ECM commands larger IACV position changes by repeating thesequential pulses to each of the four coils, until the desired position is reached. If the IACV isdisconnected or inoperative, it will remain fixed at it's last position.

EMISSION SUB SYSTEMS - Id le A i r Con t ro l System s




Duty-Control Rotary Solenoid IAC System This system uses a rotary solenoid IACV to perform idle speed stabilization. Bypass air controlis accomplished by means of a movable rotary valve which blocks or exposes a bypass port

based on command signals from the ECM. The IACV consists of two electrical coils, permanentmagnet, valve, bypass port, and bi-metallic coil.

The ECM controls IACV positioning by applying a duty cycled signal to the two electrical coils inthe IACV. By changing the duty ratio (on time versus off time), a change in magnetic field causesthe valve to rotate. Basically, as duty ratio exceeds 50%, the valve opens the bypass passageand as duty ratio drops below 50%, the valve closes the passage. If the IACV is disconnect orinoperative, the valve will move to a default position and idle rpm will be around 1000 to 1200rpm at operating temperature.

Duty-Control ACV System This system regulates air bypass volume by using an ECM duty-cycle controlled Air ControlValve (ACV). The ACV uses an electric solenoid to control a normally closed air valve whichblocks passage of air from the air cleaner to the intake manifold. Since the ACV is incapable of flowing high air volume, a separate mechanical air valve is used to perform cold fast-idle on





vehicles equipped with this system. With this type system, the ECM varies bypass airflow bychanging the duty ratio of the command signal to the ACV. By increasing the duty ratio, the ECMholds the air bypass open longer, causing an increase to idle speed. The ACV does not have

any effect on cold fast idle or warm-up fast idle speed, and is only used during starting andwarm curb-idle.

On/Off VSV Type IAC System This type of IAC system uses a normally closed Vacuum Switching Valve (VSV) to control a fixedair bleed into the intake manifold. This on/off type VSV is controlled by signals from the ECM ordirectly through the tail lamp or rear window defogger circuits.

The ECM controls the VSV by supplying current to the solenoid coil when preprogrammedconditions are met. Also, current can be supplied to the solenoid from the tail lamp or rearwindow defogger circuits by passing through isolation diodes. Engines using this IAC systemmust also use a mechanical air valve for cold fast-idle.

IAC System Control ParametersDepending on system type and application, the IAC system may perform a combination of thefollowing control functions; initial set-up, engine startup, warm-up control, feedback idle control,engine speed estimate control, electric load idle-up, learned idle speed control, and A/T idle-upcontrol. Refer to course 850 handbook for specific details concerning the operating parametersfor each of the IAC systems.





Air Valves There are two types of non-ECM controlled air valves that are used on some engines to performcold fast-idle control. The first type simply uses a thermo-wax element to vary the amount of

bypass air based on the coolant temperature. Once the engine reaches operating temperature,the air valve should be fully closed.

The second type uses a spring loaded gate balanced against a bi-metal element. As enginetemperature rises, the bi-metal element deflects to close the gate valve, thereby reducing theamount of bypass air. A heater coil surrounds the bi-metal element and is used to heat theelement whenever the engine is running (fuel pump operates). An air valve quick check can beperformed by pinching off the supply hose and observing rpm drop. The drop should be lessthan 50 rpm when the engine is warm, and should be significantly higher when the engine is

cold.





Effects of IAC Operation on Emissions & DriveabilityImproper operation of the IAC system can have significant impact on idle quality and driveability.If idle speed is too low, the engine may stall or idle very rough. If idle speed is too high, harsh

A/T gear engagement may result.

On some IAC systems, the IACV step count or ECM duty ratio may provide hints as to whether amajor correction is being made to offset a idle speed problem. For instance, if false air entrycauses idle speed to be much higher than normal, the IAC system may correct for this conditionby decreasing bypass air volume in an effort to bring idle speed back to the "target" idle speed.

The IACV step count or duty ratio may also identify a restricted air passage, misadjustedthrottle, or IAC valve problem. Observe IAC signal data at idle, while applying various "loads" tothe engine. Look for a corresponding change to IACV step count or duty ratio, as loads areplaced on the engine. Also, a signal comparison to other known good vehicles may be helpful.

IAC System Functional TestsBecause functional checks vary between the four major types of IAC systems, refer to theRepair Manual for specific procedures on performing an on-vehicle IAC inspection. On some

late model OBD-II vehicles, an active test feature will allow you to manually command IACVpositioning from fully open to fully closed. A quick check can be made by commanding achange to IACV positioning while watching for expected changes to idle rpm.





Exhaust Gas Recirculation System The Exhaust Gas Recirculation (EGR) system is designed to reduce the amount of Oxides of Nitrogen (NOx) created by the engine during operating periods that usually result in highcombustion temperatures. NOx is formed in high concentrations whenever combustiontemperatures exceed about 2500’F.

The EGR system reduces NOx production by recirculating small amounts of exhaust gases intothe intake manifold where it mixes with the incoming air/fuel charge. By diluting the air/fuelmixture under these conditions, peak combustion temperatures and pressures are reduced,resulting in an overall reduction of NOx output. Generally speaking, EGR flow should match thefollowing operating conditions:

•High EGR flow is necessary during cruising and mid-range acceleration, whencombustion temperatures are typically very high

•Low EGR flow is needed during low speed and light load conditions•No EGR flow should occur during conditions when EGR operation could adversely affect

engine operating efficiency or vehicle driveability (engine warm up, idle, wide open

throttle, etc.)

EGR Impact on the Engine Control System The ECM considers the EGR system an integral part of the entire Engine Control System (ECS). Therefore, the ECM is capable of neutralizing the negative performance aspects of EGR byprogramming additional spark advance and decreased fuel injection duration during periods of high EGR flow. By integrating fuel and spark control with the EGR metering system, engineperformance and fuel economy can actually be enhanced when the EGR system is functioningas designed.

EMISSION SUB SYSTEMS - Exhaus t Gas Rec i rcu la t ion




EGR Theory of Operation The purpose of the EGR system is to precisely regulate EGR flow under different operatingconditions, and to override flow under conditions which would compromise good engine

performance. The precise amount of exhaust gas which must be metered into the intakemanifold varies significantly as engine load changes. This results in the EGR system operatingon a very fine line between good NOx control and good engine performance.

If too much exhaust gas is metered, engine performance will suffer. If too little EGR flows, theengine may knock and will not meet strict emissions standards. The theoretical volume of recirculated exhaust gas is referred to as EGR ratio. As the accompanying graph shows, theEGR ratio increases as engine load increases.

EGR System Components

To achieve this designed control of exhaust gas recirculation, the system uses the followingcomponents:

• Vacuum Actuated EGR Control Valve

• EGR Vacuum Modulator Assembly

• ECM Controlled Vacuum Switching Valve (VSV)

EGR Control Valve The EGR control valve is used to regulate exhaust gas flow to the intake system by means of apintle valve attached to the valve diaphragm. A ported vacuum signal and calibrated spring on

one side of the diaphragm are balanced against atmospheric pressure acting on the other sideof the diaphragm. As the vacuum signal applied to the valve increases, the valve is pulledfurther from ifs seat. The key to accurate EGR metering is the EGR vacuum modulatorassembly which precisely controls the strength of the applied vacuum signal.





EGR Vacuum Modulator Because exhaust backpressure increases proportionally with engine load, the EGR vacuummodulator uses this principle to precisely control the strength of the vacuum signal to the EGRvalve. The typical EGR control system uses two ported vacuum signals from the throttle body.Port E is the first stage ported vacuum signal and Port R is the second stage ported vacuumsignal uncovered by the opening throttle valve.

When vacuum is applied from port E, the strength of the vacuum signal applied to the EGRvalve will be dependent on the amount of exhaust backpressure acting on chamber A of thevacuum modulator. When vacuum is applied from port R, the strength of the vacuum signalapplied to the EGR valve will no longer be dependent on the strength of the exhaustbackpressure signal. During this mode, the EGR signal strength is determined solely by





the strength of the vacuum signal from port E of the throttle body. The EGR vacuum modulatorprovides the ability to precisely match EGR flow rate to amount of load applied to the engine.

ECM Control led Vacuum Switching Valve (VSV)

In addition to the EGR modulator, an ECM controlled VSV is used to inhibit EGR operationduring conditions where it could adversely affect engine performance and vehicle driveability. The EGR VSV can be either normally open or closed and installed in series between thevacuum modulator and EGR valve or installed on a second port on the EGR valve. This VSVcontrols an atmospheric bleed which inhibits EGR operation any time a given set of ECMparameters are met.

ECM Override of EGRAs mentioned, the ECM is capable of inhibiting EGR flow through operation of the VSV bleed.When the ECM determines an inhibit condition, it de-energizes the VSV, blocking the vacuumsignal to the EGR valve and opening the valve diaphragm to an atmospheric bleed. Thiscauses the EGR valve to close. Typical EGR inhibit parameters are shown below.

Variations on EGR VSV Placement There are three basic variations of the EGR vacuum circuit depending on engine application.All three systems function similarly, the only difference being the placement of the VSV in thevacuum circuit and the logic of the VSV and ECM.





EGR Fault Detection SystemAn EGR malfunction detection system is incorporated into the TCCS system to warn the driverwhen the EGR system is not operating properly. The system uses an Exhaust Gas

Temperature (THG) sensor on the intake side of the EGR valve where it is exposed to exhaustgas flow whenever the EGR valve opens.

The ECM compares the THG signal with parameters stored in memory. If EGR gas temperatureis determined to be too cold when the ECM has the EGR valve enabled, the MIL will beilluminated, and a diagnostic code will be stored in ECM memory. This diagnostic configurationallows the ECM to monitor entire EGR system operation.

EGR Effect On Emissions & Driveability•Too little EGR flow may cause detonation and IM240 emissions failure for excessive NOx.Because EGR tends to reduce the volatility of the air/fuel charge, loss of EGR typically

causes detonation to occur. If EGR is commanded but doesn't flow (restricted passage inmanifold, nonfunctional valve, etc.) severe detonation will occur.

•Too much EGR flow and/or excessive flow for driving conditions may cause stumble, flatspot, hesitation, and surging. Because EGR dilutes the air/fuel charge, too much EGR fora given engine demand can cause a misfire. It is not uncommon to see tip in hesitation,stumble and surging when too much EGR is metered.

EGR System Functional TestsOn some OBD-II vehicles, the EGR system can be controlled using the active test feature of theDiagnostic Tester. This is the easiest way to verify EGR system operation and can generally be

performed as follows:

• Start the engine and allow it to reach operating temperature

• Using the Diagnostic Tester, access the Active Test menu

• Select "EGR System" from the Active Test menu

• Raise engine speed and maintain a steady 3000 rpm

• Activate the EGR VSV (turn EGR On)

• You should notice a slight drop in engine speed and a rise in EGRT gas temperature asEGR is activated

If engine speed and EGRT gas temperature does not change, the EGR system is notfunctioning and the problem may be mechanical or electrical. If the rpm drop is very slight, theproblem may be a partially blocked or restricted EGR passage.





EGR System InspectionOn other vehicles, the only way to accurately check the operation of the EGR system is toperform a systematic inspection of the entire system. The following inspection procedures arefor a 95 5S-FE Camry:

• First, inspect the EGR modulator filter and, if necessary, remove and clean the filter withcompressed air.

• "Tee" a vacuum gauge into the vacuum line between the EGR valve and VSV.

• Start the engine and confirm that it does not run rough at idle. Note: This verifies that theEGR valve is closed.• Next, connect terminals TE1 to E1 at DLC 1.

• With coolant temperature cold (A/T: below 140' F, M/T: below 131' F) and engine at 2500rpm, the vacuum gauge should indicate zero.

Note: This verifies that the VSV is inhibiting EGR flow during cold engine operations.





• Next, warm the engine to operating temperature and maintain 2500 rpm. The vacuumgauge should now indicate low vacuum (typically around 3")

Note: This verifies proper low vacuum signal to the EGR valve during light engine loadconditions.

• Next, with engine speed at 2500 rpm, connect the R port of the EGR modulator directly to

a manifold vacuum source. The vacuum gauge should now indicate high vacuum(typically around 13") and the engine should run rough.

Note: This verifies proper high signal vacuum to the EGR valve when R port vacuumoverrides the backpressure modulator.

• Disconnect terminals TE1 and El at DLC1 and reattach the EGR hoses to their originallocation.





If the problem is related to the EGR valve itself, make sure heavy carbon deposits are notkeeping the valve unseated or causing it to stick when opening. Also, if EGR valve control is OK remove the valve and check the EGR exhaust and intake passages for restrictions. Heavy

carbon deposits can be removed by using a special carbon scrapping tool.

This inspection example systematically confirms the integrity of the EGR valve, VSV,backpressure modulator, system hoses, and EGR passages. Once the suspectpart/component is identified, it should be individually tested and then repaired or replaced asnecessary. Because slight model to model variations exist between EGR systems, refer to theRepair Manual for specific EGR system inspection procedures.





Evaporative Emission Control SystemApproximately 20% of all hydrocarbon (HC) emissions from the automobile originate fromevaporative sources. The Evaporative Emission Control (EVAP) system is designed to storeand dispose of fuel vapors normally created in the fuel system; thereby, preventing its escape tothe atmosphere. The EVAP system delivers these vapors to the intake manifold to be burnedwith the normal air/fuel mixture. This fuel charge is added during periods of closed loopoperation when the additional enrichment can be managed by the closed loop fuel controlsystem. Improper operation of the EVAP system may cause rich driveability problems, as wellas failure of the Two Speed Idle test or Enhanced I/M evaporative pressure or purge test.

The EVAP system is a fully closed system designed to maintain stable fuel tank pressureswithout allowing fuel vapors to escape to the atmosphere. Fuel vapor is normally created in thefuel tank as a result of evaporation. It is then transferred to the EVAP system charcoal canisterwhen tank vapor pressures become excessive. When operating conditions can tolerateadditional enrichment, these stored fuel vapors are purged into the intake manifold and addedto the incoming air/fuel mixture.

EMISSION SUB SYSTEMS - Evapora t i ve Em iss ion Cont ro l Sys tem




Toyota vehicles use two different types of evaporative emission control systems:

• Non-ECM controlled EVAP systems use solely mechanical means to collect and purge

stored fuel vapors. Typically, these systems use a ported vacuum purge port and a Thermo Vacuum Valve (TVV) to prohibit cold engine operation.

• ECM controlled EVAP systems uses a manifold vacuum purge source in conjunction witha duty cycled Vacuum Switching Valve (VSV). This type of EVAP system has the ability toprovide more precise control of purge flow volume and inhibit operation.

Non-ECM Control led EVAP SystemNon-ECM controlled EVAP systems typically use the following components:

• Fuel tank

• Fuel tank cap (with vacuum check valve)

• Charcoal canister (with vacuum & pressure check valves)

• Thermo Vacuum Valve (TVV)

• Ported vacuum purge port (port P; on throttle body)

EVAP System OperationUnder some conditions, the fuel tank operates under a slight pressure to reduce the possibility

of pump cavitation due to fuel vaporization. Pressure is created by unused fuel returning to thetank and is maintained by check valve #2 in the charcoal canister and the check valve in the fueltank cap.

Under other conditions, as fuel is drawn from the tank, a vacuum can be created in the tankcausing it to collapse. This is prevented by allowing atmospheric pressure to enter the tankthrough check valve #3 in the charcoal canister or the fuel tank cap check valve. The EVAPsystem is designed to limit maximum vacuum and pressure in the fuel tank in this manner.

When the engine is running, stored fuel vapors are purged from the canister whenever thethrottle has opened past the purge port (port P) and coolant temperature is above a certain

point (usually around 129' F). Fuel vapors flow from the high pressure area in the canister, pastcheck valve #1 in the canister, through the Thermo Vacuum Valve (TVV), to the low pressurearea in the throttle body. Atmospheric pressure is allowed into the canister through a filterlocated on the bottom of the canister. This ensures that purge flow is constantly maintainedwhenever purge vacuum is applied to the canister.

When coolant temperature falls below a certain point (usually around 95’F), the TVV preventspurge from taking place by blocking the vacuum signal to check valve #1.





ECM Controlled EVAP System OperationIntroduced on the'95 Avalon for CA, this system is similar to the Non-ECM controlled systems,except that an ECM controlled Vacuum Switching Valve (VSV) is used in place of the ThermoVacuum Valve (TVV). The VSV is normally closed and duty cycle controlled, which means the

ECM rapidly opens and closes the VSV passage to provide precise, variable control of purgeflow volume and inhibit operation.

Because this system uses a manifold vacuum purge port, it may provide slight purge flowduring idle if conditions can tolerate its enrichment. The ECM uses engine speed, intake airvolume, coolant temperature, and oxygen sensor information to control EVAP operation.

EVAP Purge System MonitoringBy monitoring the oxygen sensor and injection pulse width as the canister is being purged, theECM can detect the reduction of exhaust oxygen content and corresponding decrease ininjection pulse width to correct for this momentary rich condition. In this manner, the ECM can

detect a failure in the EVAP purge control system and store a DTC to alert the vehicle operator of the malfunction. Purge flow monitoring is only used on '95 and later OBD-II equipped vehicles.

EVAP Effect on Emissions and DriveabilityDuring Two Speed Idle tests, it is not uncommon for vehicles to fail off idle tailpipe tests forexcessive CO emissions due to normal evaporative purge cycle operation. It is also possiblefor the charcoal canister to become saturated with liquid fuel to the degree that it becomesunserviceable.





To avoid emissions failures due to normal evaporative emissions purge cycle, the vehicleshould not be tested after long hot soak periods, prolonged idle or after having been left insitting in the sun on a hot day. All of these conditions will cause large amounts of fuel vapor to

store in the charcoal canister. To put the EVAP system through it's normal purge cycle, thevehicle can be driven at highway speeds for five minutes. This should purge any vapor from thecanister which would normally accumulate during the above mentioned conditions.

If the canister continues to cause high CO emissions after a normal purge cycle has beenperformed, it is possible that the canister is irrecoverably saturated. If the EVAP is suspected aspotential cause of high CO emissions failure or rich driveability problems, the following checksshould be made:

• Isolate the EVAP system from the engine intake by removing the purge port hose fromthrottle body port.

• Test vehicle with EVAP system isolated.

If the EVAP system is determined to be at fault, use procedures in the appropriate RepairManual to inspect the charcoal canister, filter, check valves, TVV or VSV and the related vacuumplumbing.





Enhanced I/M EVAP Purge and Pressure Test DiagnosisEvaporative System Purge and Pressure Tests will be required as a part of Enhanced I/Mtesting. If the vehicle fails for either purge or pressure, checks can be made to verify the

operation and integrity of evaporative control system.

EVAP System Pressure Test Diagnosis The Enhanced I/M Evaporative Pressure Test is performed by filling the EVAP vapor line andfuel tank with nitrogen to a pressure of 14 inches of water (approximately 0.5 psi). If the systemmaintains at least 8 inches of water pressure after 2 minutes, it passes the test.

If the EVAP system fails the pressure test, a leak exists either in the vapor vent line between thecanister and tank, the fuel tank itself, or the fuel cap. Visual checks may or may not identify thesource of leak(s) in the system; however, you should never pressurize the EVAP system withshop air! Doing this would introduce oxygen into the EVAP system were it could combine withfuel vapors and create a very explosive condition. Secondly, the system is tested at very lowpressure which would make accurate, pressure regulation difficult. If the system wasaccidentallypressurized beyond this point, severe damage to the system may result.





EVAP Pressure Testing Using Special Test Equipment The best way to test and identify leak(s) that cause a pressure test failure is to use specialEVAP pressure testing equipment available from aftermarket suppliers. This equipment allows

you to perform an actual pressure test, in addition to having features that help you locate theleak. There are many variations and differences between test equipment and procedures, butfor the sake of example, here is the test procedure for an EVAP pressure tester that usespressurized nitrogen gas:

1. Disconnect the fuel tank vapor line from the canister and attach the pressure tester to thisline.

Note: The tester may have an adapter that allows you to connect the pressure line between thetank filler neck and the fuel cap.

2. Activate the tester and pressurize the line until 14 inches of water pressure is maintained.

3. Observe the pressure gauge and note if the pressure begins to drop.

Note: It is normal for pressure to initially rise or fall slightly then stabilize after a few seconds. This is caused by the initial temperature variation between the nitrogen and EVAP fuelvapors. Once temperatures stabilize, the pressure will equalize if no leak exist.

4. If the pressure drops dramatically, listen for leaks from the fuel cap, tank seams, and hoses.

5. Check for frayed or cracked hoses, poor connections, damaged fuel tank seams, faulty fuel

cap gasket or check valve.

6. The leak may be found by spraying the suspected area with soapy water and looking forbubbles.

7. Special ultrasonic leak detectors are now available that can "listen" for the exact frequenciescaused by these low pressure leaks. Another method uses the exhaust analyzer to check forthe escape of fuel vapors (HC) from the leaky part/component.

Note: The drawback to using the exhaust analyzer is the limited amount of fuel vapors that existin EVAP system (fuel tank). If the leak is not quickly identified, all HC vapors will escape

leaving only a nitrogen (inert gas) leak to locate.

8. If the leak cannot be identified by the completion of the test, select the manual mode thatprovides a constant pressure on the system.

9. Once the leaky part/component is identified, perform the needed repair or replacement.





EVAP Purge Test Diagnosis The evaporative purge test is performed during the IM240 transient (drive cycle) test. A flowtransducer is placed in series with the purge line between the canister and engine. In order to

pass, the system must purge at least 1 liter of flow by the end of the IM240 drive cycle. Toyotavehicles with properly operating EVAP systems normally purge 25 liters or more by thecompletion of drive cycle.

If the EVAP system fails the purge test, a problem exists with the purge port, the purge hose tothe canister, or the charcoal canister itself. Since 1 liter of flow is such a nominal amount, thetest really only verifies whether the system is purging or not. There are checks that you canmake to confirm vacuum to the canister or the effects of purge flow on the air/fuel mixture;however, the only real way of measure actual flow volume is to use a flow transducer, similar tothe one used in the actual purge test.

EVAP Purge Test Using Special Equipment The most accurate method of checking EVAP purge flow is to check the system in the samemanner in which it was tested. EVAP purge flow testers (sometimes combined with pressuretesters) are currently available from aftermarket sources and typically operates as follows:

1. Precondition the vehicle by running the engine until it reaches operating temperature.

2. Connect the tester's flow transducer into the EVAP purge line between the engine andevaporative canister.

3. With the engine off, zero the tester to calibrate the purge flow reading.

4. Next, with the engine idling, start the timer and observe the purge flow rate and accumulatedpurge volume on the tester display.





Note: On TVV equipped systems that use a ported vacuum purge source, no purge should takeplace during idle, however, on systems using a VSV, the ECM may command a very slightamount of flow during idle.

5. Slowly raise engine speed and maintain a steady 2500 rpm. During this period purge flowshould increase dramatically and, on a properly functioning EVAP system, 1 liter of flowshould be surpassed in a matter of seconds.

6. If the system does not flow at least 1 liter within the 240 second test period or it marginallypasses the test, perform the following functional checks to help identify the suspect parts orcomponents.

Note: Since most vehicles flow 25 liters or more during the same period, marginal passesshould also be checked and repaired since these systems are not functioning properly

and will probably fail in future tests.

7. Once the problem has been identified and repaired, perform this test again to confirmsufficient improvements in purge volume.





EVAP System CheckIf the system fails the purge flow test or flows very little, the following Evaporative EmissionSystem Check may help identify problems causing no or low purge flow. The following

inspection procedures are for a '95 5S-FE Camry:

1. First, visually inspect the fuel tank, fuel cap, canister, lines and connections for anydamage, cracks, fuel leakage, or deterioration and repair or replace as necessary.

2. Check the canister for a clogged filter or stuck check valve by performing the following:

• Apply low pressure compressed air (0.68 psi) into the fuel tank vapor port (port A) of the canister and confirm that air flows out from all other canister ports.

Note: Airflow from canister ports is difficult to detect.

• Next, apply low pressure compressed air to the purge port (port B) of the canister andconfirm that air does not flow out from any of the other ports.

Note: Replace the canister if a problem is detected with either of the checks above.

• Clean the canister filter by applying air pressure (43 psi) to the tank vapor port (port A)while holding the purge port (port B) closed with your finger.

Note: If carbon blows out during this test replace the canister.





3. Check the operation of the TVV by performing the following:

• Disconnect the hoses from the TVV and then attach a hand operated vacuum pump tothe lower port of the TVV.

• With coolant temperature cold (below 95’F), operate the vacuum pump and confirmthat air does not flow (vacuum is held) from the upper port to the lower port.

Note: It is normal for some TVWs to allow a slight amount of airflow when cold.

• Next, allow coolant temperature to rise above 129' F. Operate the vacuum pump andconfirm that air now flows (vacuum bleeds off) between the top port and the lowerport.

Note: If the TVV fails any of the checks above, replace it.

This EVAP check example systematically confirms the integrity of the evaporative canister and TVV. Once repair or replacement is made, retest the system to confirm sufficient purgeimprovement needed to pass a retest. Because slight variations exist between evaporativesystem tests, refer to the Repair Manual for specific EVAP test procedures and specifications.





Positive Crankcase Ventilation SystemDuring normal compression stroke, a small amount of gases in the combustion chamberescapes past the piston. Approximately 70% of these "blowby" gases are unburned fuel (HC)

that can dilute and contaminate the engine oil, cause corrosion to critical parts, and contributeto sludge build up. At higher engine speeds, blowby gases increase crankcase pressure thatcan cause oil leakage from sealed engine surfaces.

The purpose of the Positive Crankcase Ventilation (PCV) system is to remove these harmfulgases from the crankcase before damage occurs and combine them with the engine's normalincoming air/fuel charge. Fuel injected Toyota vehicles use two different types of closed PCVsystems to prevent the escape of crankcase vapors into the atmosphere:

• Fixed Orifice PCV System

• PCV System Using Variable Flow PCV Valve

Fixed Orif ice PCV SystemOn some early Toyota EFI vehicles, a fixed orifice PCV system is used to meter blowby from thecrankcase into the intake manifold, where they would be consumed during normal engineoperation. This system is simple in design and construction, and provides crankcaseventilation based on the size of the fixed orifice valves and the normal operating characteristicsof intake manifold vacuum. The two fixed orifice valves are used to balance the strength of vacuum applied to the crankcase as engine operating conditions change. The biggestdrawback of this type system is that blowby production does not always match intake manifoldvacuum characteristics.

EMISSION SUB SYSTEMS - Pos i t i ve Crank cas e Vent i la t io n Sys tem




PCV System Using Variable-Flow PCV ValveUnlike fixed orifice type systems, PCV systems that use a variable-flow PCV valve moreaccurately match ventilation flow with blowby production characteristics. By accurately matchingtheses two factors, crankcase ventilation performance is optimized, while engine performanceand driveability remains unaffected.





PCV System Components The variable-flow type PCV systems are also very simple in design and consists of thefollowing components:

• PCV Valve

• PCV purge hose

• Breather hose

PCV System OperationLike the previous system, this system also uses manifold vacuum to draw crankcase vaporsback into the intake manifold. Typically, blowby production is the greatest during high loadoperations and very light during idle and light load operations. Since the characteristics of manifold vacuum do not match the flow requirements needed for proper crankcase ventilation,

a PCV valve is used to regulate blowby flow back into the intake manifold.

• During id le and deceleration, blowby production is very low, but intake manifold vacuumis very high. This causes the pintle inside the PCV valve to fully retract against springtension. The positioning of the pintle provides a small vacuum passage and allows forlow blowby flow to the combustion chamber.

• During low load cruising, the pintle inside the PCV valve is positioned somewhat in thecenter of its travel. This positioning allows a moderate volume of blowby flow into thecombustion chamber.





• During acceleration and high load operations, blowby production is very high. The pintleextends out further from the restriction allowing the maximum flow of blowby into thecombustion chamber. During extremely high engine loads, if blowby volume exceeds the

ability of the PCV valve to draw in the vapors, the excess blowby flows through thebreather hose to the air cleaner housing where it can enter the combustion chamber.

• When the engine is off or it backfires, spring tension closes the valve completelypreventing the release of blowby into the intake manifold. The valve closes during abackfire to prevent the flame from traveling into the crankcase where it could ignite theenclosed fuel vapors.

PCV System Effects on Emissions and DriveabilityBecause PCV operation is factored into the proper operation of the feedback control system,problems with the PCV system may disrupt the normal air/ fuel ratio balance. A plugged PCVvalve will prevent the normal flow of crankcase vapors into the engine and can result in a richer

than normal air/fuel mixture. A plugged crankcase breather hose may cause the engine toconsume oil because of the increased level of crankcase vacuum.

In addition, depending on the location of the fresh air breather hose, a nonfunctional valve orrestricted vacuum hose can cause oil contamination in the air cleaner housing or throttle borecoking. Always suspect and check the PCV system if you find traces of oil in the air intakesystem.





If the crankcase becomes diluted with fuel, carbon monoxide (CO) levels will likely increasebecause the PCV system will meter extra fuel vapor into the intake system. Always replace fueldiluted engine oil and identify and resolve the problem causing the fuel contaminated.

Although there are no mandatory maintenance intervals for the PCV system, periodically checkthe system for a plugged or gummed PCV valve and damaged hoses. Replace suspectcomponents as necessary. Since PCV flow rates differ between vehicle models, it is importantto use the correct replacement PCV valve to ensure proper operation. The installation of anincorrect valve may cause engine stalling, rough idle and other driveability complaints. Thus,never install universal type PCV valves!

PCV System Functional Tests The following RPM Drop Test may be used as a basic quick check to confirm that the PCVsystem is functioning:

• Start the engine and allow it to reach operating temperature

• On TCCS equipped vehicles, connect TE to E1 at the diagnostic connector

• Allow the engine to stabilize at idle

• Pinch or block the hose between the PCV valve and vacuum source

• Typically, engine rpm should drop around 50 rpm If engine rpm does not change, checkthe PCV valve and system hoses for blockage. Replace components as necessary and

then retest the system.





Catalytic Converter Regardless of how perfect the engine is operating, there will always be some harmful by-products of combustion. This is what necessitates the use of a Three-Way Catalytic (TWC)Converter. This device is located in-line with the exhaust system and is used to cause adesirable chemical reaction to take place in the exhaust flow.

Essentially, the catalytic converter is used to complete the oxidation process for hydrocarbon(HC) and carbon monoxide (CO), in addition to reducing oxides of nitrogen (NOx) back tosimple nitrogen and carbon dioxide.

TWC Construction Two different types of Three-Way Catalytic Converters have been used on fuel injected Toyotavehicles. Some early EFI vehicles used a pelletized TWC that was constructed of catalystcoated pellets tightly packed in a sealed shell, while later model vehicles are equipped with amonolith type TWC that uses a honeycomb shaped catalyst element. While both types operatesimilarly, the monolith design creates less exhaust backpressure, while providing amplesurface area to efficiently convert feed gases.

EMISSION SUB SYSTEMS - Catalyt ic Con ver t er




The Three-Way Catalyst, which is responsible for performing the actual feed gas conversion, iscreated by coating the internal converter substrate with the following key materials:

• Platinum/Palladium; Oxidizing catalysts for HC and CO

• Rhodium; Reducing catalyst for NOx

• Cerium; Promotes oxygen storage to improve oxidation efficiency The diagram belowshows the chemical reaction that takes place inside the converter.

TWC OperationAs engine exhaust gases flow through the converter passageways, they contact the coatedsurface which initiate the catalytic process. As exhaust and catalyst temperatures rise, thefollowing reaction occurs:

• Oxides of nitrogen ( NOx) are reduced into simple nitrogen (N2) and carbon dioxide(CO2)

• Hydrocarbons (HC) and carbon monoxide (CO) are oxidized to create water (H2O) andcarbon dioxide (CO2)





Catalyst operating efficiency is greatly affected by two factors; operating temperature and feedgas composition. The catalyst begins to operate at around 550' F.; however, efficient purificationdoes not take place until the catalyst reaches at least 750' F. Also, the converter feed gasses

(engine-out exhaust gases) must alternate rapidly between high CO content, to reduce NOxemissions, and high O2 content, to oxidize HC and CO emissions.

Effects of Closed Loop Control on TWC Operation To ensure that the catalytic converter has the feed gas composition it needs, the closed loopcontrol system is designed to rapidly alternate the air/fuel ratio slightly rich, then slightly lean of

stoichiometry. By doing this, the carbon monoxide and oxygen content of the exhaust gas alsoalternates with the air/fuel ratio. In short, the converter works as follows:

• When the A/F ratio is leaner than sto ichiometry, the oxygen content of the exhauststream rises and the carbon monoxide content falls. This provides a high efficiencyoperating environment for the oxidizing catalysts (platinum and palladium). During thislean cycle, the catalyst (by using cerium) also stores excess oxygen which will bereleased to promote better oxidation during the rich cycle.

• When the A/F ratio is richer than stoichiometry, the carbon monoxide content of theexhaust rises and the oxygen content falls. This provides a high efficiency operating

environment for the reducing catalyst (rhodium). The oxidizing catalyst maintains itsefficiency as stored oxygen is released.





As mentioned in the beginning of this section, precise closed loop control relies on accuratefeedback information provided from the exhaust oxygen sensor. The sensor acts like a switchas the air/fuel ratio passes through stoichiometry.

Closed loop fuel control effectively satisfies the three way catalyst's requirement for amplesupplies of both carbon monoxide and oxygen. Generally speaking, if the closed loop controlsystem is functioning normally, and fuel trim is relatively neutral, you can be assured that the airinduction and fuel delivery sub-systems are also operating normally. If the closed loop controlsystem is not working properly, the impact on catalytic converter efficiency, and ultimatelyemissions, can be significant.





Effects of Oxygen Sensor DegradationSince the oxygen sensor is the heart of the closed loop control system, proper operation iscritical to efficient emission control. There are several factors which can cause the oxygensensor signal to degrade and they include the following:

• Silicon contamination from chemical additives, some RTV sealers, and contaminatedfuel.

• Lead contamination can be found in certain additives and leaded motor fuels.

• Carbon contamination is caused by excessive short trip driving and/or malfunctionsresulting in an excessively rich mixture.

The effects of sensor degradation can range from a subtle shift in air/fuel ratio to a totallyinoperative closed loop system. With respect to driveability and emissions diagnosis, a siliconcontaminated sensor will cause the most trouble.

When silicon burns in the combustion chamber, it causes a silicon dioxide glaze to form on the

oxygen sensor. This glaze causes the sensor to become sluggish when switching from rich tolean, and in some cases, increases the sensor minimum voltage on the lean switch. Thiscauses the fuel system to spend excessive time delivering a lean mixture.





It is often difficult to identify a sensor which is marginally degraded, and in many cases, vehicledriveability may not be effected significantly. With the advent of IM240 emissions testing,however, marginal sensor degradation may cause some vehicles to fail the NOx portion of theloaded mode test.

The impact of a slightly lean mixture has a dual effect on emissions. A leaner mixture meanshigher combustion temperatures so more NOx is produced during combustion. Additionally,because less carbon monoxide is available in catalyst feed gas, the reducing catalyst efficiencyfalls off dramatically. The end result is a vehicle which may fail an IM240 test for excessive NOx.





As previously mentioned, the O2S signal voltage must fluctuate above and below 0.45 volts atleast 8 times in 10 seconds at 2500 rpm with the engine at operating temperature. During therich swing, voltage should exceed 550 mv and during the lean swing should fall below 400 mv.

O2S signal checks can be made using the Autoprobe feature of the Diagnostic Tester, digitalmultimeter, or 02S/RPM check using the Diagnostic Tester. Refer back to the oxygen sensortests in the closed loop control section for specific test procedures.

Effects of TWC DegradationNow that we understand the effects of O2S degradation on catalyst efficiency, let's look at theeffects of a catalytic converter failure. Keep in mind, there are many different factors that cancause its demise.

• Poor engine performance as a result of a restricted converter. Symptoms of a restrictedconverter include; loss of power at higher engine speeds, hard to start, poor acceleration

and fuel economy.• A red hot converter indicates exposure to raw fuel causing the substrate to overheat. This symptom is usually caused by an excessive rich air/fuel mixture or engine misfire. If the problem is not corrected, the substrate may melt, resulting in a restricted converter.

• Rotten egg odor results from excessive hydrogen sulfide production and is typicallycaused by high fuel sulfur content or air/fuel mixture imbalance. If the problem is severeand not corrected, converter meltdown and/or restriction may result.

• IM emission test failure may occur if catalyst performance falls below its designedefficiency level. Perform additional tests to confirm that the problem is in fact converterefficiency and not the result of engine or emission sub-system failure. Never use an

emission test failure as the only factor in replacing a catalytic converter! If you do,

you may not be fixing the actual cause of the emission failure.

Causes of TWC ContaminationLike the oxygen sensor, the most common cause of catalytic converter failure is contamination.Examples of converter contaminants include:

• Overly rich air/fuel mixtures will cause the converter to overheat causing substratemeltdown.

• Leaded fuels, even as little as one tank full, may coat the catalyst element and renderthe converter useless.

• Silicone from sealants (RTV, etc.) or engine coolant that has leaked into the exhaust,

may also coat the catalyst and render it useless.

There are other external factors that can cause the converter to degrade and requirereplacement. Thermal shock occurs when a hot converter is quickly exposed to coldtemperature (snow, cold fuel, etc.), causing it to physically distort and eventually disintegrate.Converters that have sustained physical damage (seam cracks, shell puncture, etc.) shouldalso be replaced as necessary.





TWC Functional ChecksBefore a converter is condemned and replaced, it is crucial that any problem(s) that may havecontributed to the damage and failure of the converter is identified and repaired. If not, the

replacement converter will soon fail!

Also, in order to accurately check catalytic converters, all engine mechanical, engine controlsystems, and emission sub-systems must be in proper working order or your results will beinaccurate. Remember, the converter relies on a narrow feed gas margin or efficiency suffers.

There are a number of tests that can be performed on catalytic converters; however, no one testshould be used to verify the complete integrity and conversion efficiency of the converter. Thefollowing are examples of typical TWC checks.

Visual Inspection

The first check, and the easiest, is to perform a thorough visual inspection of the converter andrelated hardware. Many converter problems have obvious symptoms that are easily identifiedduring a visual inspection. Look for the following; pinched exhaust pipe, physical damage to theinsulator or converter shell, cracked or broken seams, excessive rust damage, mud or ice inthe tailpipe, etc.

Rattle TestPerform a rattle test by firmly hitting the converter shell with the center of your palm (avoid hittingit too hard or you may damage it!) If the substrate is OK it should sound solid. If it rattles, thesubstrate has disintegrated and the converter should be replaced.





Restricted Exhaust System CheckDriveability comments like "lacks power under load" or "difficult to start, acts flooded and alsolacks power" may indicate a restricted exhaust. In extreme cases the exhaust may be so

restrictive that the engine will not start. Generally speaking, here's how to test for a restrictedexhaust system:

• Attach a vacuum gauge to an intake manifold vacuum source.

• Allow the engine to reach operating temperature.

• From idle, raise engine speed to approximately 2000 rpm.

• Note: The vacuum reading should be close to normal idle reading.

• Next, quickly release the throttle.

Note: The vacuum reading should momentarily rise then smoothly drop back to a normalidle reading. If the vacuum rises slowly or does not quickly return to normal level, the

exhaust system may be restricted.

If the catalyst has disintegrated, it is likely that contamination has also restricted the muffler.Don't overlook that possibility. If the engine will not start, try disconnecting the exhaust system atthe manifold and see if the engine will start.

Lead Contamination CheckA common cause of converter contamination is lead poisoning. As mentioned, lead reducesconverter efficiency by coating the catalyst element. Special lead detecting test paper (or paste)is available from aftermarket suppliers that checks for the presence of lead in the tailpipe.Follow the specific instructions provided by the test paper manufacturer.





TWC Efficiency Quick Check (CA Vehicles)On CA vehicles equipped with sub-O2 sensors, a quick check of TWC operation can be made

by comparing the signal activity of the main oxygen sensor with the sub-oxygen sensor. Sincethe main O2S in located upstream of the converter and the sub-O2S is located downstream, asignal comparison would indicate whether a catalytic reaction is taking place inside theconverter. If the catalyst is operating, the main O2S signal should normally toggle rich/lean,while the sub-O2 sensor should react very slowly (similar to a bad main O2S signal.) Main andsub O2S signals can be observed using the graphing display of the Diagnostic Tester (OBD-II)or V-BoB on other models.

NOTE: Before any catalyst efficiency tests are performed, it is important that both the engineand converter are properly preconditioned. Remember, proper feed gas conversion cannot takeplace until the closed loop control system is actively maintaining ideal mixture and the catalysthas reached operating temperature. To ensure these conditions are met, particularly during

cold ambient conditions, operate the engine off-idle until the TWC is sufficiently heated. Thiswill ensure optimal catalyst conversion efficiency.





Secondary Air Injection

Pulsed Secondary Air Injection System (PAIR)Combustion gases that enter the exhaust manifold are not completely burned and wouldcontinue to bum if not limited by the amount of oxygen in the exhaust system. To decrease thelevel of emissions emitted from the tailpipe, the Pulsed Secondary Air Injection (or Air Suction)system is used to introduce air into the exhaust flow, thereby allowing combustion to continuewell into the exhaust system. This prolonged combustion (oxidation) period helps to lower thelevels of HC and CO emissions that are forwarded to the catalytic converter. Additional air in theexhaust system also ensures that an adequate supply of oxygen is provided to the converter forcatalyst oxidation.

Pulsed Secondary Air Injection (PAIR) systems do not use an air pump, but rely solely on thepressure differential that exists between atmospheric pressure and exhaust vacuum pulsationto draw air into the exhaust manifold.

System Components Toyota PAIR system uses the following components:

• PAIR valve (with reed valves)• Vacuum Switching Valve (VSV)• Check valve• Resonator• Air passage hoses

EMISSION SUB SYSTEMS - Secon dary Ai r In jec t io n




PAIR System OperationExhaust pressure is high when the exhaust valve opens to allow combustion gases into the

exhaust manifold. However, once the valve closes, exhaust pressure drops below atmosphericpressure to create a vacuum in the exhaust manifold. This explains why exhaust pressurerapidly pulsates above and below atmospheric pressure.

The PAIR system promotes HC and CO oxidation by adding additional oxygen into the exhaustmanifold during cold engine operation and deceleration (when very specific parameters aremet). These operating conditions typically produce higher levels of HC and CO emissions.

This system simply provides a controlled air passage between atmosphere and the exhaustmanifold. Whenever exhaust manifold pressure drops below atmospheric pressure, fresh airfrom the high pressure zone (atmosphere) flows through the system and enters the exhaust

manifold where it promotes emission oxidation.

PAIR Valve The PAIR system should only operate when needed; thus, a PAIR valve is used to controlsystem air flow. It is simply a vacuum control diaphragm valve, similar to an EGR valve, that isopened to allow secondary air flow and closed to prohibit flow. The PAIR valve assembly alsocontains reed valves that prevent exhaust gases from entering system and possibly damagingit, when exhaust pressure exceeds atmospheric pressure.

EMISSION SUB SYSTEMS - Secon dary Ai r In jec t io n

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