automotive engine performance by james d. halderman © 2009 pearson education, inc. pearson prentice...

Automotive Engine PerformanceBy James D. Halderman

© 2009 Pearson Education, Inc.Pearson Prentice Hall - Upper Saddle River, NJ 07458

Chapter Objectives• Prepare for the ASE Engine Performance (A8) certification

test content area “E” (Computerized Engine Controls Diagnosis and Repair).

• Explain the purpose and function of OBD II.• Describe how the PCM performs active and passive tests

of the computerized engine controls system.• Describe the standardized OBD-II DTCs and terminology.• Discuss continuous and non-continuous monitors.• Explain the difference between enhanced and generic OBD

II.



• On-Board Diagnostics OBD I– CARB 1st OBD regulation

• OBD Gen I (OBD I)– All vehicles sold in – CA 1988

» Warning lamp » Transmit DTCs» Electronic system

monitoring of the HO2S, EGR valve, and evaporative purge solenoid

On-Board Diagnostics Generation-II (OBD-II) Systems

FIGURE 10-1



• OBD-II Objectives– CARB defines an OBD-II-equipped to do

following: • Detect component degradation

– Faulty emission-related system that prevents compliance with federal emission standards.

– Alert driver of needed emission-related repair or maintenance.

– Standardized DTCs, accept a generic scan tool– 1996 & later vehicles




• Clean Air Act of 1990– EPA develop new regulations for OBD

• OBD II Primary purpose emission reduction • OBD I primary purpose of OBD I (1988) detect

faults– OBD-II regulations require sensors be tested & all

exhaust emission control devices » Verified for proper operation.» New vehicles must pass Federal Test Procedure

(FTP)





• Federal Test Procedure (FTP)– Exhaust emissions tested 505 seconds, rollers

• Simulate urban drive cycle around downtown LA– IM 240 a 240-second version of 505-second FTP – Exhaust emissions are within 1.5 times the FTP limits– Computer must do the following:

» Test all exhaust emission system components» Actively operate the system and measure the results.» Continuously monitor emissions do not exceed 1.5 X

FTP» Check engine operation for misfire» Turn on MIL PCM senses a fault» Record a freeze frame» Flash MIL if an engine misfire occurs



Diagnostic Executive– PCM Incorporates Special Software

• GM call it diagnostic executive. • Manages operation of all OBD-II monitors

– Controlling sequence of steps » Execute diagnostic tests and monitors



MONITORS• Organized Method of Testing

– Monitors• Simply tests, PCM performs to evaluate components

& systems – If component, system failure detected while a monitor is

running– DTC stored & MIL illuminated by second trip– Two types of monitors used: continuous and

noncontinuous



MONITORS• Continuous Monitors

– Conditions met • Continuous monitors begin to run• Run for remainder of vehicle drive cycle• 3 continuous monitors are as follows:

– Comprehensive component monitor (CCM)– Misfire monitor– Fuel trim monitor



MONITORS• Comprehensive Component Monitor (CCM)

– Watches sensors & actuators • Sensor values are constantly compared

– Known-good values stored in PCM memory– CCM, internal program in PCM

• Monitor– Failure in any electronic component or circuit– Provides input or output signals to the PCM



MONITORS• Misfire Monitor

– Looks at engine misfire• PCM uses information received • From crankshaft position sensor (CPK)

– Calculate time between edges of reluctor» As well as rotational speed and acceleration

– Comparing acceleration of each firing event– PCM determines if a cylinder is not firing correctly

• Misfire type A• Misfire type B



MONITORS• Fuel Monitor

– PCM monitors short & long term fuel trim• Constantly updated adaptive fuel tables are stored in

long-term memory (KAM)• PCM uses data to compensate for wear & aging of

fuel system components– MIL illuminates when PCM determines fuel trim values– Reached and stayed at their limits for too long a period



MONITORS• Noncontinuous Monitors

– Run once per vehicle drive cycle• Noncontinuous monitors are:

– O2S monitor & O2S heater monitor

– Catalyst monitor– EGR monitor– EVAP monitor– Secondary AIR monitor– Transmission monitor– PCV system monitor– Thermostat monitor



Diagnostic Trouble Code Priority

• CARB Mandated All DTCs– Stored according to individual priority

• DTCs with a higher priority overwrite lower priority– OBD-II System DTC Priority include:

» Priority 0 – Non-emission related codes» Priority 1 – One-trip failure of two-trip fault for non-fuel,

non-misfire codes» Priority 2 – One-trip failure of two-trip fault for fuel or

misfire codes» Priority 3 – Two-trip failure or matured fault of non-fuel,

non-misfire codes» Priority 4 – Two-trip failure or matured fault for fuel or

misfire codes



OBD-II Monitor Information Summary

• Comprehensive Components Monitor (CCM)– Circuits & components covered by CCM

• Do not include those directly monitored by another monitor

– OBD II requires inputs from powertrain components to PCM – Tested for rationality, & outputs to powertrain components

from PCM – Tested for functionality




• Continuous Running Monitors– Monitors run continuously, stop if they fail

• Examples:– Fuel system: rich/lean– Misfire: catalyst damaging/FTP (emissions)– Two-trip faults (except early gen catalyst damaging misfire)– MIL, DTC, freeze frame after two consecutive faults– Freeze frame is priority 2 on first trip– Freeze frame is priority 4 on maturing trip– 3 consecutive good trips in a similar condition window to

are used to extinguish the MIL




• Once Per Trip Monitors– Monitor runs once per trip, pass or fail

• O2 response, O2 heaters, EGR, purge flow EVAP leak, secondary air, catalyst

• Two-trip DTCs– MIL, DTC, freeze frame after 2 consecutive faults– Freeze frame is priority 1 on first trip– Freeze frame is priority 3 on maturing trip– 3 consecutive good trips are used to extinguish the MIL– 40 warm-up cycles used to erase DTC & freeze frame




• Exponentially Weighted Moving Average (EWMA)– Monitors

• Catalyst monitor• EGR monitor

– PCM runs 6 consecutive failed tests; fails in 1-trip– 3 consecutive failed tests on next trip, then fails– Freeze frame is priority 3– 3 consecutive good trips are used to extinguish the MIL– 40 warm-up cycles are used to erase DTC and freeze frame



ENABLING CRITERIA • Diagnostic Executive (Task Mgr) Enabling

Criteria – Internal director to keep track

• When each monitor should run• Each monitor has enabling criteria• Conditions must be met

– Before task manager will give go-ahead for each monitor to run



Monitor Running Conditions• Overview

– Monitor running conditions required• Diagnostic monitor to run.

– E.G.: Specific RPM, ECT, MAP, run time, VSS, etc.



Monitor Running Conditions• Pending

– Some situations PCM will not run a monitor• MIL is illuminated

– Fault is stored from another monitor– PCM postpones monitors pending resolution of original

fault– PCM does not run the test until the problem is remedied



Monitor Running Conditions• Conflict

– PCM does not run a monitor• Another monitor is in progress

– Effects of another monitor running result in erroneous failure

– Conflict present, monitor not run until conflicting condition passes

– Monitor will run later after conflicting monitor has passed



Monitor Running Conditions• Suspend

– PCM may not allow a two-trip fault to mature• PCM will suspend the maturing fault

– If a condition exists that may induce erroneous failure– Prevents illuminating MIL for wrong fault– Allows more precise diagnosis



Monitor Running Conditions• Rationality Test

– PCM constantly monitors • Inputs for electrical opens and shorts

– Tested for rationality– Means input signal is compared – Against other inputs and information– See if it makes sense under current conditions



Monitor Running Conditions• FREQUENTLY ASKED QUESTION

– What Does “Rationality Check” Mean?• PCM programmed to detect faults

– Do not seem rational– Engine operating for 20 minutes coolant temp changes

» 195°F to -40°F– Determines not possible (rational) defaults to fail-safe temp– Before OBD-II regulations, increase fuel delivered– OBD-II computer can reason that there must be a fault– Continue to deliver fuel for proper operation– Not too much that could affect the exhaust emissions



OBD-II Drive Cycle• Trip

– Key-On/Key-Off condition • Key-on, conditions for a particular test • To be performed followed by a key off

– Conditions called enable criteria– EGR test engine at normal operating temperature– Decelerating for a minimum amount of time



OBD-II Drive Cycle• Warm-Up Cycle

– Trip with engine temperature increase of • At least 40°F • Engine temperature reaches 160°F (71°C).

– E.G.: MIL is deactivated– Original code remains in memory until 40 warm-up cycles

are completed– Without fault reappearing



OBD-II Drive Cycle• MIL Condition: Off

– PCM has not detected any faults• Emissions-related component or system

– MIL circuit is not working



OBD-II Drive Cycle• MIL Condition: On Steady

– Condition indicates a fault• Emissions-related component

– System that could affect vehicle emission levels



OBD-II Drive Cycle• MIL Condition: Flashing

– Condition indicates• Misfire or fuel control system fault• That could damage catalytic converter



OBD-II Drive Cycle• MIL Off

– PCM turns off the MIL• Following actions or conditions occur:

– Codes cleared with scan tool– Power to PCM removed for an extended period of time – Driven on 3 consecutive trips with a warm-up cycle

» Meets code set conditions without PCM detecting faults



OBD-II DTC Numbering Designation

• DLC– Data Link

Connector

FIGURE 10-2




• Diagnostic Trouble Code (DTC)– Scan tool required, retrieve DTCs

• Every OBD-II scan tool• Read

– Generic SAE DTCs

• Major categories:– Pxxx codes – powertrain DTCs– Bxxx codes – body DTCs – Cxxx codes – chassis DTCs – Uxxx codes – network DTCs

FIGURE 10-3




• DTC Numbering Explanation– Number in hundredth position

• Indicates specific vehicle system – Subgroup that failed. – Consistent for P0xxx and P1xxx type codes

» Example: P0100 – Air metering and fuel system fault




• FREQUENTLY ASKED QUESTION– Is There a Generic Drive Cycle?

• Readiness tests (sometimes called flags)– Tests performed on all of the monitored systems on Tech2 – Published drive cycles for each OEM – Generic drive cycle usually allows all monitors to run– Coolant temperature < 122°F (50°C) IAT within 11°F (6°C)

» ECT temperature– Fuel tank filled from 15% to 85% capacity before test




• Types of DTCs– Not all OBD-II DTCs

• Same importance– Each type of DTC has different requirements




• Type A Codes– Type “A” DTC is emission related

• MIL turned on first trip – PCM detected a problem. – Engine misfire or a very rich or lean air-fuel




• Type B Codes– B code stored, MIL turned

• During 2nd consecutive trip• Alerting driver to fact

– Diagnostic test was performed and failed




• Type C and D Codes– Non-emission-related diagnostic tests

• Cause lighting of MIL lamp – Vehicle is so equipped

• Type C codes are also called – Type C1 codes and D codes are also called type C0 codes




• OBD-II Freeze Frame– OBD II requires PCM – Take a "snapshot" or freeze frame

• All data at instant an emission-related DTC is set– Scan tool (Tech 2) required




• NOTE: – OBD II requires one freeze frame

• Data be stored– Instant an emission-related DTC is set– GM provides expanded data about DTC– Beyond that required– Retrieving this enhanced data – Requires Tech 2 vehicle-specific scan tool




• Freeze Frame – Items:

• Listed below– Calculated load value & RPM– Short-term and long-term fuel trim percent– Fuel system pressure (on some vehicles)– Vehicle speed (mph)– Engine coolant temperature– Intake manifold pressure– Closed/open-loop status– Fault code that triggered the freeze frame– If a misfire code is set, identify cylinder misfiring



FREEZE FRAME • DTC Should Not Be Cleared

– From vehicle computer memory• Unless corrected

– OBD II requires snap shot of engine parameters– Instant a DTC was set– Help determine what caused the fault– Help verify that the fault has been corrected– Problem corrected, PCM automatically clears DTC– After 40 consecutive warm-up cycles no faults detected – Misfire, rich or lean condition codes require 80 cycles– Codes can also be erased by using scan tool



FREEZE FRAME• NOTE:

– Disconnecting battery• May not erase OBD-II DTCs

– Or freeze frame data– GM recommends using Tech 2 to erase DTCs – Rather than disconnecting battery– Memory for the radio, seats

» Learned engine operating parameters» Lost if the battery is disconnected



FAILURE RECORDS• Enhance Freeze Frame Data

– Required by OBD II• GM also provide additional information

– Called failure records– Data included in failure records – Allow technician to see more about operating conditions– Vehicle was experiencing when failure occurred



FAILURE RECORDS• REQUENTLY ASKED QUESTION

– What Are Pending Codes?• Pending codes are set operating conditions met

– Component or circuit is not within the normal range– Conditions have not yet been met to set a DTC– Sensor may require 2 consecutive faults before DTC set– Scan tool displays a pending code or a failure– Driveability concern could also be present– Pending code can help technician determine root cause – Before customer complains of MIL



NEED for FUEL TRIM • Fuel Trim Purpose

– Provide catalytic converter• Rich and a lean air-fuel mixture

– Rich mixture (lack of extra oxygen) needed – Reduce NOX exhaust emissions– Lean mixture (excessive oxygen) needed – Oxidize HC and CO into harmless

» Carbon dioxide (CO2) and water (H2O) vapor



NEED for FUEL TRIM • Exhaust Always Rich

– Catalytic converter cannot reduce • CO and HC emissions

– Exhaust is always lean, catalytic converter – Cannot reduce NOX emissions– Air-fuel mixture must alternate between rich and lean– PCM provides this alternating mixture– Using oxygen sensor, short-term and long-term fuel trim – Program to accomplish this feat



SHORT-TERM FUEL TRIM • STFT % Measurement

– Amount PCM adding or subtracting• EFI systems use O2S

– Determine whether exhaust is rich or lean

– Without O2S, control of fuel delivery

– Belongs to PCM alone using programmed PWM commands – Based on other sensor inputs– ECT, TPS, and MAP



SHORT-TERM FUEL TRIM • Operating in Closed Loop

– O2S signal can modify or change• Preprogrammed fuel delivery

– Fuel trim is expressed as a percentage (%), (+) or (-)– Amount of fuel different from anticipated amount– Small vacuum leak were to occur

– O2S produces lower voltage signal interpreted by PCM

– Air-fuel mixture is too lean– Pulse width increased to compensate for vacuum leak– Additional fuel added as positive short-term fuel trim



SHORT-TERM FUEL TRIM • NOTE:

– Before 1996, GM referred to STFT• Integrator

– Expressed it in binary numbers from 0 to 255– 128 was the midpoint and a reading of ±10 from 128 – (118-138) was usually considered to be a normal reading

FIGURE 10-4



SHORT-TERM FUEL TRIM • STFT of +20%

– Indicates 20% additional fuel added• Achieve proper air-fuel mixture

– -20% short-term fuel trim indicates – Fuel had to be removed by shortening injector pulse width– Achieve the proper air-fuel mixture.– STFT varies air-fuel mixture so catalytic converter– Reduce HC, CO, and NOX exhaust emissions– Large vacuum leak occurs, fuel delivery must be increased

» For a Longer Period– EFI computers must use a long-term fuel trim program



LONG-TERM FUEL TRIM • LTFT: Add or Subtract Fuel

– Larger amount of time • Than short-term fuel trim

– LTFT looked at by technician as a guide– PCM has been adding or subtracting fuel – Accomplish the proper air-fuel mixture– Vacuum hose split open, engine leaner than normal– STFT attempts to add fuel right away to adjust– Leak remained for longer than a few seconds– PCM revises to long-term fuel trim– Compensate for the leak over a larger period of time



LONG-TERM FUEL TRIM • LTFT Makes an Adjustment

– STFT can still make short and quick changes• In air-fuel mixture needed

– Provide the catalytic converter with an alternating rich– Then lean, then rich, and so forth, exhaust



LONG-TERM FUEL TRIM • REAL WORLD FIX

– Red S-10 Pickup Truck Story• 4-cylinder 2.2-liter engine was replaced

– Replacement engine never did run correctly, idle & low speeds

– -25% long-term fuel trim, oxygen sensor was measuring a very rich exhaust from spent exhaust gases

– Oxygen sensor indicating a false rich condition» None of the false rich conditions was found

– Incorrect EGR gasket was found– Caused exhaust gases to flow into the cylinders all time



Fuel Trim as Diagnostic Aid • Fuel Trim Values

– Only be observed with scan tool• Display both short-term and long-term fuel trim

– For system diagnosis, refer to the long-term fuel trim – Because it represents a longer amount of time (history)– Greater amount of mixture correction



Fuel Trim as Diagnostic Aid • NOTE

– STFT and LTFT• Make corrections to fuel delivered

– Achieve proper air-fuel mixture– +25% LTFT, will require PCM to deliver 30% more– Calibrated amt of fuel to achieve proper air-fuel mixture– Engine is now operating with correct air-fuel mixture– LTFT # tells technician what PCM had to do to achieve– Proper mixture



FUEL TRIM CELLS• STFTs and LTFTs

– React to oxygen sensor voltage• Modify fuel delivery

– Most vehicles set aside different cells for – Each combination of engine speed (RPM) and load– PCM can then correct for slight differences in fuel mixture– Some GM vehicles use 16 cells – Plus 2 for deceleration and 2 for idle only



Fuel Trim Cell Diagnosis• Data Observed

– During same condition as problem• Two cells for idle

– One with air conditioning (A/C) on and one for A/C off– Customer’s concern only occurs when A/C is on– Observe fuel trim numbers on Tech 2 – Engine operating at idle and with the A/C on



Fuel Trim Cell Diagnosis• Problem at 55 mph (90 km/h)

– Looking at fuel trim in service bay• At idle will not help at all

– Vehicle must be driven under similar conditions– Duplicate the condition when the problem occurs– Only then will the correct fuel cell be displayed– Long-term fuel trim information should be valid– See fuel trim diagnostic chart



Fuel Trim Cell Diagnosis• Fuel Trim Diagnostic Chart



Fuel Trim & Misfire Codes• Fuel Trim

– Misfire-related code sets• Driven under conditions similar when fault detected

– Before PCM will deactivate the MIL– Similar conditions are:– Engine speed within 375 RPM of speed stored in freeze

frame data when the code set– Engine load ±10% of load value stored in freeze frame data

when the code set– Temperature conditions similar to temperature value stored

in freeze frame data when the code set



GENERIC OBD II• All OBD-II Vehicles

– Must be able to display data• Generic (also called global) scan tool

– Under nine different modes of operation– Information may be helpful if a generic scan tool used– Diagnose GM vehicles instead of using a TECH 2



GENERIC OBD II

• Global Scan Tool– 9 modes of operation, include:

• Mode One: Current powertrain data • Mode Two: Freeze frame data• Mode Three: Diagnostic trouble codes• Mode Four: Clear, reset DTCs• Mode Five: Oxygen sensor monitor test results• Mode Six: Non-continuously monitored systems • Mode Seven: continuously monitored systems• Mode Eight: bidirectional control of onboard systems• Mode Nine: module identification



Summary1. If the MIL is on, retrieve the DTC and follow the

manufacturer's recommended procedure to find the root cause of the problem.

2. All monitors must have the enable criteria achieved before a test is performed.

3. OBD-II vehicles use a 16-pin DLC and common DTCs.

4. OBD II includes generic (SAE), as well as, vehicle manufacturer’s specific DTCs and data display.



Review Questions

1. What does the PCM do during a drive cycle to test emission-related components?

2. What is the difference between a type A and type B OBD-II DTC?

3. What is the difference between a trip and a warm-up cycle?

4. What could cause the MIL to flash?

automotive engine performance by james d. halderman © 2009 pearson education, inc. pearson prentice...

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