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Anti-Lock Braking Systems(ABS) for Trucks, Tractors

and BusesMaintenance Manual No. 28

Revised 4-98

For C Version ECUs


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Copyright 1998 Meritor WABCO

Service Notes

This Maintenance Manual describes the correct service, replacement installation and operation proceduresfor Meritor WABCO Anti-Lock Braking Systems for Trucks, Tractors and Buses. The information contained inthis manual was current at the time of printing and is subject to change without notice or liability.

You must follow your company's safety procedures when you install or repair this equipment. Be sure youunderstand all procedures and instructions before you begin to repair this unit. Meritor WABCO uses the

following symbols and instructions to warn of possible safety problems and to supply information that willprevent damage to the equipment.

WARNINGA WARNING indicates that you must followa procedure exactly. Otherwise, seriouspersonal injury can occur.

CAUTIONA CAUTION indicates that you must follow

a procedure exactly. Otherwise, damage toequipment or components can occur. Seriouspersonal injury can also result, in addition todamaged or malfunctioning equipmentor components.

NOTEA NOTE indicates an operation, procedure orinstruction that is important for proper service.A NOTE can also supply information that canhelp to make service quicker and easier.

TORQUEThis symbol indicates that you must tighten

fasteners to a specific torque value.


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Table of Contents

Asbestos and Non-Asbestos Fiber Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Section 1: IntroductionAbout This Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Vehicle Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Vehicle Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3ECU Mounting Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

ABS Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

How ABS Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

ABS Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Optional Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Section 2: Automatic Traction Control (ATC)Optional ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Deep Snow and Mud Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

ATC Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Section 3: TroubleshootingGeneral Maintenance Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Suggested Diagnostic Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Blink Code Reference Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Blink Code Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Blink Code Facts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

Using the Blink Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

Blink Code Diagnostic Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Working with Blink Code Diagnostics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Blink Code Diagnostics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Optional Test Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

Meritor WABCO Test Adaptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

Table 1 Test Adaptor Measurement Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20Table 2 ABS and ATC Valve Function Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Final Test for a Tractor Equipped with ABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

For a Tractor Equipped with ABS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

MPSI Pro-Link 9000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Testing and Diagnostic Screens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Testing Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Ignition Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

Sensor Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

Sensor Adjustment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

ABS Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

ATC Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

Dynamometer Testing Vehicles with ATC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Tire Size Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

Section 4: Removal & InstallationComponent Removal and Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

Section 5: WiringWiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30


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Page 1

Asbestos and Non-Asbestos Fibers

ASBESTOS FIBER WARNINGThe following procedures for servicing brakes are recommended to reduceexposure to asbestos fiber dust, a cancer and lung disease hazard. MaterialSafety Data Sheets are available from Meritor.

Hazard Summary

Because some brake linings contain asbestos, workers who service brakes must understandthe potential hazards of asbestos and precautions for reducing risks. Exposure to airborneasbestos dust can cause serious and possibly fatal diseases, including asbestosis (a chroniclung disease) and cancer, principally lung cancer and mesothelioma (a cancer of the lining ofthe chest or abdominal cavities). Some studies show that the risk of lung cancer amongpersons who smoke and who are exposed to asbestos is much greater than the risk fornon-smokers. Symptoms of these diseases may not become apparent for 15, 20 or more yearsafter the first exposure to asbestos.

Accordingly, workers must use caution to avoid creating and breathing dust when servicingbrakes. Specific recommended work practices for reducing exposure to asbestos dustfollow. Consult your employer for more details.

Recommended Work Practices

1. Separate Work Areas. Whenever feasible, service brakes in a separate area awayfrom other operations to reduce risks to unprotected persons. OSHA has set a maximumallowable level of exposure for asbestos of 0.1 f/cc as an 8-hour time-weighted averageand 1.0 f/cc averaged over a 30-minute period. Scientists disagree, however, to whatextent adherence to the maximum allowable exposure levels will eliminate the risk ofdisease that can result from inhaling asbestos dust. OSHA requires that the following signbe posted at the entrance to areas where exposures exceed either of the maximum

allowable levels:DANGER: ASBESTOS

CANCER AND LUNG DISEASE HAZARDAUTHORIZED PERSONNEL ONLY

RESPIRATORS AND PROTECTIVE CLOTHINGARE REQUIRED IN THIS AREA

2. Respiratory Protection. Wear a respirator equipped with a high-efficiency (HEPA)filter approved by NIOSH or MSHA for use with asbestos at all t imes when servicingbrakes, beginning with the removal of the wheels.

3. Procedures for Servicing Brakes.

a. Enclose the brake assembly within a negative pressure enclosure. The enclosureshould be equipped with a HEPA vacuum and worker arm sleeves. With the enclosure inplace, use the HEPA vacuum to loosen and vacuum residue from the brake parts.

b. As an alternative procedure, use a catch basin with water and a biodegradable,non-phosphate, water-based detergent to wash the brake drum or rotor and other brakeparts. The solution should be applied with low pressure to prevent dust from becomingairborne. Allow the solution to flow between the brake drum and the brake support or thebrake rotor and caliper. The wheel hub and brake assembly components should be

thoroughly wetted to suppress dust before the brake shoes or brake pads are removed.Wipe the brake parts clean with a cloth.

c. If an enclosed vacuum system or brake washing equipment is not available, employersmay adopt their own written procedures for servicing brakes, provided that the exposurelevels associated with the employer's procedures do not exceed the levels associatedwith the enclosed vacuum system or brake washing equipment. Consult OSHA regulationsfor more details.

d. Wear a respirator equipped with a HEPA filter approved by NIOSH or MSHA for usewith asbestos when grinding or machining brake linings. In addition, do such work in anarea with a local exhaust ventilation system equipped with a HEPA filter.

e. NEVER use compressed air by itself, dry brushing, or a vacuum not equipped with aHEPA filter when cleaning brake parts or assemblies. NEVER use carcinogenic solvents,flammable solvents, or solvents that can damage brake components as wetting agents.

4. Cleaning Work Areas. Clean work areas with a vacuum equipped with a HEPA filter orby wet wiping. NEVER use compressed air or dry sweeping to clean work areas. Whenyou empty vacuum cleaners and handle used rags, wear a respirator equipped with aHEPA filter approved by NIOSH or MSHA for use with asbestos. When you replace a HEPAfilter, wet the filter with a fine mist of water and dispose of the used filter with care.

5. Worker Clean-Up. After servicing brakes, wash your hands before you eat, drink orsmoke. Shower after work. Do not wear work clothes home. Use a vacuum equipped witha HEPA filter to vacuum work clothes after they are worn. Launder them separately. Do notshake or use compressed air to remove dust from work clothes.

6. Waste Disposal. Dispose of discarded linings, used rags, cloths and HEPA filters withcare, such as in sealed plastic bags. Consult applicable EPA, state and local regulationson waste disposal.

Regulatory Guidance

References to OSHA, NIOSH, MSHA, and EPA, which are regulatory agencies in the UnitedStates, are made to provide further guidance to employers and workers employed within theUnited States. Employers and workers employed outside of the United States should consultthe regulations that apply to them for further guidance.

NON-ASBESTOS FIBER WARNINGThe following procedures for servicing brakes are recommended to reduceexposure to non-asbestos fiber dust, a cancer and lung disease hazard. MaterialSafety Data Sheets are available from Meritor.

Hazard Summary

Most recently manufactured brake linings do not contain asbestos fibers. These brake liningsmay contain one or more of a variety of ingredients, including glass fibers, mineral wool,aramid fibers, ceramic fibers and silica that can present health risks if inhaled. Scientistsdisagree on the extent of the risks from exposure to these substances. Nonetheless,exposure to silica dust can cause silicosis, a non-cancerous lung disease. Silicosis graduallyreduces lung capacity and efficiency and can result in serious breathing difficulty. Somemedical experts believe other types of non-asbestos fibers, when inhaled, can cause similardiseases of the lung. In addition, silica dust and ceramic fiber dust are known to the State ofCalifornia to cause lung cancer. U.S. and international agencies have also determined thatdust from mineral wool, ceramic fibers and silica are potential causes of cancer.

Accordingly, workers must use caution to avoid creating and breathing dust when servicingbrakes. Specific recommended work practices for reducing exposure to non-asbestos dustfollow. Consult your employer for more details.

Recommended Work Practices

1. Separate Work Areas. Whenever feasible, service brakes in a separate area awayfrom other operations to reduce risks to unprotected persons.

2. Respiratory Protection. OSHA has set a maximum allowable level of exposure forsilica of 0.1 mg/m3 as an 8-hour time-weighted average. Some manufacturers ofnon-asbestos brake linings recommend that exposures to other ingredients found innon-asbestos brake linings be kept below 1.0 f/cc as an 8-hour time-weighted average.Scientists disagree, however, to what extent adherence to these maximum allowableexposure levels will eliminate the risk of disease that can result from inhalingnon-asbestos dust.

Therefore, wear respiratory protection at all times during brake servicing, beginning withthe removal of the wheels. Wear a respirator equipped with a high-efficiency (HEPA) filterapproved by NIOSH or MSHA, if the exposure levels may exceed OSHA or manufacturersrecommended maximum levels. Even when exposures are expected to be within themaximum allowable levels, wearing such a respirator at all times during brake servicingwill help minimize exposure.

3. Procedures for Servicing Brakes.

a. Enclose the brake assembly within a negative pressure enclosure. The enclosureshould be equipped with a HEPA vacuum and worker arm sleeves. With the enclosure inplace, use the HEPA vacuum to loosen and vacuum residue from the brake parts.

b. As an alternative procedure, use a catch basin with water and a biodegradable,non-phosphate, water-based detergent to wash the brake drum or rotor and other brakeparts. The solution should be applied with low pressure to prevent dust from becomingairborne. Allow the solution to flow between the brake drum and the brake support or the

brake rotor and cal iper. The wheel hub and brake assembly components should bethoroughly wetted to suppress dust before the brake shoes or brake pads are removed.Wipe the brake parts clean with a cloth.

c. If an enclosed vacuum system or brake washing equipment is not available, carefullyclean the brake parts in the open air. Wet the parts with a solution applied with apump-spray bottle that creates a fine mist. Use a solution containing water, and, ifavailable, a biodegradable, non-phosphate, water-based detergent. The wheel hub andbrake assembly components should be thoroughly wetted to suppress dust before thebrake shoes or brake pads are removed. Wipe the brake parts clean with a cloth .

d. Wear a respirator equipped with a HEPA filter approved by NIOSH or MSHA whengrinding or machining brake linings. In addition, do such work in an area with a localexhaust ventilation system equipped with a HEPA filter.

e. NEVER use compressed air by itself, dry brushing, or a vacuum not equipped with aHEPA filter when cleaning brake parts or assemblies. NEVER use carcinogenic solvents,flammable solvents, or solvents that can damage brake components as wetting agents.

4. Cleaning Work Areas. Clean work areas with a vacuum equipped with a HEPA fil ter oby wet wiping. NEVER use compressed air or dry sweeping to clean work areas. Whenyou empty vacuum cleaners and handle used rags, wear a respirator equipped with a

HEPA filter approved by NIOSH or MSHA, if the exposure levels may exceed OSHA ormanufacturers' recommended maximum levels. When you replace a HEPA fi lter, wet thefilter with a fine mist of water and dispose of the used filter with care.

5. Worker Clean-Up. After servicing brakes, wash your hands before you eat, drink orsmoke. Shower after work. Do not wear work clothes home. Use a vacuum equipped witha HEPA filter to vacuum work clothes after they are worn. Launder them separately. Do noshake or use compressed air to remove dust from work clothes.

6. Waste Disposal. Dispose of discarded linings, used rags, cloths and HEPA filters withcare, such as in sealed plast ic bags. Consult applicable EPA, state and local regulationson waste disposal.

Regulatory Guidance

References to OSHA, NIOSH, MSHA, and EPA, which are regulatory agencies in the UnitedStates, are made to provide further guidance to employers and workers employed within theUnited States. Employers and workers employed outside of the United States should consultthe regulations that apply to them for further guidance.


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Notes

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Page 3

Section 1Introduction


About This ManualThis manual contains service, troubleshooting,and repair information for the Meritor WABCOAnti-Lock Braking System (ABS) and ABS with

Automatic Traction Control (ATC) for trucks,tractors, and buses manufactured after December1990. If your ABS-equipped vehicle wasmanufactured before this date, call MeritorWABCO customer service, 800-535-5560, forassistance.

Vehicle SpecificationsTo use this manual you need the followinginformation about your vehicle:

Where is the ECU mounted?

How is the ABS configured?

What are the tire sizes used on the vehicle? (SeeSection 3, "Troubleshooting".)

Is it equipped with ATC? (See Section 2,Automatic Traction Control [ATC].)

Use the chart shown in Table A to record vehicleidentification data.

Vehicle Identification

ECU Mounting Locations

The Electronic Control Unit (ECU) may be mountedin the cab or on the frame of the vehicle.

ABS Configuration

The ABS configuration is determined by thenumber of wheel end sensors and modulatorvalves. There are three possibilities:

4 wheel end sensors, 4 modulator valves (4S/4M) 6 wheel end sensors, 4 modulator valves (6S/4M)

6 wheel end sensors, 6 modulator valves (6S/6M)

Typical ABS configurations are illustrated inSection 3, "Troubleshooting", Figures3.43.9.

How ABS WorksThe Meritor WABCO Anti-Lock Braking System(ABS) is an electronic system that monitors andcontrols wheel speed during braking. The systemworks with standard air brake systems.

The ABS monitors wheel speed at all times andcontrols braking during emergency situations. TheMeritor WABCO ABS improves vehicle stabilityand control by reducing wheel lock during braking

In the unlikely event of a malfunction in the system,the ECU will disable all or only a portion of the ABS,returning the affected wheels to normal braking.

An electronic control unit (ECU) receives andprocesses signals from the wheel speed sensors.When the ECU determines a wheel lockupcondition, the unit activates an appropriatemodulator valve, and air pressure is reduced.When the wheel speed enters the stable regionagain, the pressure is automatically increased.

There is an ABS warning lamp to let the driver and the service technician know the system isworking. ABS warning lamps for systems installedon buses, trucks, or tractors are located on thedash or instrument panel, depending on the makeand model of the vehicle.

Table A Vehicle Identification Chart

Vehicle ECUMounting

ABS Configuration Tire Sizes OptionalATC

Model YearManufacturer

VIN Cab Frame 4S/4M 6S/4M 6S/6M Front Rear Y N


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Page 4

ABS Components

The Electronic Control Unit (ECU) is the brain ofthe system. It receives information from thesensors and sends signals to the ABS valves.The ECU may be mounted in the cab or on theframe of the vehicle. As illustrated, cab- andframe-mounted ECUs use a different styleconnector. Figure 1.1.

NOTEDo not open the ECU. Opening the ECU to gainaccess to the internal components will void thewarranty.

The tooth wheel is mounted on the hub of eachmonitored wheel. Figure 1.2.

A sensor is installed so that its end is against thetooth wheel. The sensor continuously sends wheelspeed information to the ECU. On a four-channel

ABS, two sensors are installed on the steering axleand two additional sensors are mounted on onedrive axle. The sensors on the steering axle areinstalled in the steering knuckle. The sensors onthe drive axle are mounted in a block attached tothe axle housing. Figure 1.3.

The sensor clip holds the sensor in place at thetooth wheel. Figure 1.4.

Figure 1.1

1 Cab-Mounted2 Frame-Mounted

Figure 1.2

Figure 1.3

Figure 1.4


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Page 5


An ABS modulator valve controls air pressure toeach affected brake during ABS function. Figure 1.5.

During normal braking, compressed air flowsthrough the ABS valve to the brake chambers.During ABS operation, the ABS valve adjusts airpressure to the brake chambers to control brakingand prevent wheel lock.

The ABS valve is usually located on a frame rail orcross member, between the relay valve or quickrelease valve and the brake chamber.

An alternative to individual valves is the ABS valvepackage. It combines two ABS modulator valvesand one relay valve. Figure 1.6.

The in-cab ECU harness provides electricalconnections for the power, ground, warning lamp,and communication connections to the ECU.Depending on your vehicle set-up, it may alsoinclude the blink code switch and lamp. Figure 1.7.

The chassis harness provides the electricalconnections for the sensors and valves.

Sensor Extension Cables connect the sensor to theECU. Figure 1.8.

Figure 1.5

1 Out (Port 2)2 In (Port 1)

Figure 1.6

Figure 1.7

1 Cab Harness2 Chassis Harness

Figure 1.8


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The ABS Modulator Valve Cable connects the ABSvalve to the ECU. Figure 1.9.

The ABS warning lamp comes on when theignition switch is activated. The lamp goes outwhen the speed of the vehicle reachesapproximately 4 mph (6 km/h). If the warning lamp

remains lit or comes on at any other time duringvehicle operation, it signals a malfunction in theABS. Figure 1.10.

Optional Test Equipment:

See Section 3, "Troubleshooting", foroperating instructions.

The Meritor WABCO test adaptor helps service andtroubleshoot the ABS system. Use with

cab-mounted ECUs only. Figure 1.11.

The MPSI Pro-Link 9000 with the Meritor WABCOcartridge, available from Kent-Moore, lets you testABS components. Figure 1.12.

Figure 1.9

Figure 1.10

Figure 1.11

Figure 1.12


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Section 2Automatic Traction Control (ATC)

Section 2AutomaticTractionControl (ATC)

Optional ATCATC is an option available on ABS-equippedvehicles. It helps move vehicles on slipperysurfaces and reduces drive wheel overspin.

ATC works automatically in two different ways:1. If a drive wheel starts to spin, ATC brakes that

wheel and transfers engine torque to thewheels with better traction.

2. If all drive wheels spin, ATC reduces enginetorque to provide improved traction.

If drive wheels spin during acceleration, the ATCindicator lamp comes on and stays lit. Todetermine if a vehicle has ATC, look for anindicator lamp on your dash or instrument panelmarked ATC, ASR, or wheel spin. (Somevehicles without ATC have a wheel spin lamp.)Figure 2.1.

Deep Snow and Mud Switch

A Deep Snow and Mud switch may be includedwith ATC. This feature increases available traction

for vehicles on extra soft surfaces like slush ormud. The selection switch and indicator lamp arelocated on the dash. When this feature is selected,the indicator lamp blinks continuously. Figure 2.2.

ATC Components

ATC uses two solenoid valves, two double-check

valves, and a wiring harness with ATC connectors.

ATC solenoid valves are usually mounted on theframe toward the rear of the vehicle.

The air line between the ATC valve and the double

check valve must gradually slope toward the ATCvalve. This allows condensation to drain out of theATC valve exhaust.

See Section 3, "Troubleshooting", Section 4,"Removal & Installation", and Section 5, "Wiring"for additional ATC information.

Figure 2.1

Figure 2.2

Figure 2.3


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Notes

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Page 9

Section 3Troubleshooting


General MaintenanceInformationThere is no regularly scheduled maintenancerequired for the Meritor WABCO ABS or ABS/ATC.

However, ABS does not change current vehiclemaintenance requirements.

Troubleshooting

Suggested Diagnostic Tools

Standard: Blink Code Reference Information(see below).

Optional: Meritor WABCO Test Adaptor.

Optional: Pro-Link 9000.

Blink Code Reference InformationTo troubleshoot a possible ABS fault, use theblink code diagnostics built into the system. Beforeyou begin, you should be familiar with thefollowing definitions.

Blink Code Definitions

Blink Code: A series of blinks or flashes thatdescribe a particular ABS system configurationand fault.

Blink Code Cycle: A set of three series of flashes,each set separated by a 2.5 second pause. The firstset of flashes represents the system set-up:

1 flash = 6S/6M

2 flashes = 4S/4M

4 flashes = 6S/4M

The last two sets identify the system fault.

Blink Code Switch: A switch that activates blinkcode diagnostic capabilities. Switch locations vary,depending on the make and model of the vehicle.Figure 3.1.

CAUTIONYou must turn the blink code switch to the OFFposition before engaging in normal operation.If the switch is left in the ON position, reducedengine power can result (for vehicles equippedwith ATC only).

Figure 3.1

1 Steering Column2 ABS Check Switch3 Engine Brake Relay4 Diagonal 1 10 Amp Fuse5 Diagonal 2 10 Amp Fuse6 Diagonal 1 Valve Relay (VR1)7 Warning Lamp Relay8 Diagonal 2 Valve Relay (VR2)9 ECU 5 Amp Fuse10 Blink Code Switch with Light


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Erasing a fault: The process of clearing a fault fromthe ECU:

1. After an Existing fault has been corrected

2. After an Intermittent fault has been displayed

After the fault has been cleared, the blink codedisplays a new code. Or, if there are no otherfaults, the blink code displays system O.K.(i.e., 2-0-0).

Fault: An ABS malfunction detected and stored inmemory by the Meritor WABCO ECU. Systemfaults may be existing or intermittent.

Existing Fault: An active ABS fault; for example, asensor circuit malfunction on the left front steeringaxle that currently exists. An existing fault must berepaired before it can be cleared from memory.

Intermittent Fault: An inactive fault; for example, a

loose wire that caused a system fault to register.An intermittent fault does not require repair beforeit can be cleared from memory.

IF . . . ABS warning lamp comes onand stays on after:

Ignition turned OFF, then ONand

Vehicle driven in excessof 4 mph (6 km/h) . . . . . . Fault is Existing

IF . . . ABS warning lamp comes onand stays on after:

Vehicle driven in excess

of 4 mph (6 km/h)andABS warning lamp goes out after:Ignition turned OFF, then ON

andVehicle again driven inexcess of 4 mph(6 km/h) . . . . . . . . . . Fault is Intermittent

Blink Code Facts

As long as the ignition key and blink codeswitch remain in the ON position, the blinkcode will repeat.

Intermittent fault codes can be erased fromthe ECU memory, but the condition that causedthe fault could still exist. Record intermittentfault codes and make any necessaryadjustments or repairs to the vehicle.

After using the blink code, turn the blink codeswitch OFF before resuming normal operation.

Using the Blink Code

Servicing Alert

An ABS warning lamp alerts drivers to a possible

system malfunction. If the ABS lamp stays onduring normal vehicle operation, the driver knowsthe vehicle needs to be serviced.

Blink Code Display

The blink code is displayed on one of the followinglamps installed in the vehicle:

An independent blink code lamp or acombination blink code switch and lamp.

An ATC lamp located on the vehicle instrumentpanel (for ABS/ATC-equipped vehicles.)

Lamp locations vary, depending on the make andmodel of the vehicle.

Figures3.2 and 3.3 illustrate the blink code cycle.

Figure 3.2

Figure 3.3


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Blink Code Diagnostic Procedure Follow these steps to use the blink code:

Working with Blink Code Diagnostics When using blink code diagnostics, the followingconditions may occur:

Step Action System Response Action

I

Turn IgnitionKey ON.and

Turn Blink CodeSwitch ON.

ABS lamp comes on and stays on.

Blink Code lamp comes on afterapproximately 5 seconds, then goes off.

At the end of 5 seconds, blink codecycle begins.

Observe lamps.

IIIdentify the 3-digitblink code.

First set of flashes (indicates systemconfiguration).

Pause. . . . . . . . . . . . . . . . . . . .

Second set of flashes.

Pause.

Third set of flashes. . . . . . . . . .

Observe and record blink code.

After blink code is identified, turn blink code switchOFF, cycle will continue until all three sets of flasheshave been displayed.

After COMPLETE blink code cycle, turn ignition OFF.Look up 3-digit code on Diagnostics Chartor BlinkCode Card, TP-94157.

IIIRepeat Step I todetermine status offault: Intermittent orExisting.

If a new code or a system O.K. code(i.e., 2-0-0) appears, fault wasIntermittent.

NOTE: System O.K. code indicatesfault erased from ECU memory.

If code repeats, fault is existing (active)and must be repaired.

Keep a record of fault for future reference.

NOTE: Make necessary adjustments or repairs tovehicle to prevent future occurrences.

Perform repair listed on Diagnostics Chartor TP-94157.

Repeat procedure until System O.K. code received.

Step Condition Cause Action

I Lamp doesnot light.

Loose or burned out bulb. Check bulb.

Check connections.

Make necessary repairs.

Voltage not within acceptablerange (11-15 volts).

Check connections.

Measure voltage.

Make necessary repairs.

I, III Code continuesto repeat.

Ignition and blink code switch notturned off.

Turn Blink Code switch off.

Wait for lamp to stop flashing.

Turn Ignition off.Fault not repaired. Review Diagnostics Chartor TP-94157 to ensure all

possible conditions were corrected.

Verify all repair work.

Fault not erased from ECUafter report.

Repeat procedure until System O.K. code received.

II Code not listed onDiagnostics Chartor TP-94157.

Verify code (repeat Steps I and II).

Contact Meritor WABCO Customer Service(800-535-5560) for assistance.


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Blink Code Diagnostics Use the following chart to identify blink codes.

Additional 6S/6M and 6S/4M blink codes follow this table.

Fault Code

Blink Code* Location Cause Solution

1-0-02-0-04-0-0

N/A No Faults System O.K. No action needed.

1-6-62-6-64-6-6

Voltage Relay 1

Low voltage to the diagonal relayor defective relay.

Check vehicle voltage orreplace relay if needed.1-6-7

2-6-74-6-7

Voltage Relay 2

1-6-8

2-6-84-6-8 Right Front Wheel Erratic wheel speed signal fromthe steering axle.

Check for loose wheel

bearings, faulty sensor wiringconnections, excessive hubrunout, a sensor gap that istoo wide, or damage to toothwheels on the steering axle.

1-6-92-6-94-6-9

Left Front Wheel

1-6-102-6-104-6-10

Right Front Wheel

Sensor circuit failure onsteering axle.

Check sensor, sensor cableand cable connections.1-6-11

2-6-114-6-11

Left Front Wheel

1-6-12

2-6-124-6-12 Right Front Wheel Steering axle sensor outof adjustment.

Adjust sensors onsteering axle.1-6-13

2-6-134-6-13

Left Front Wheel

1-7-02-7-04-7-0

Left Rear Wheel

Erratic wheel speed fromdrive axle.

Check for loose wheelbearings, faulty sensor wiringconnections, excessive hubrunout, sensor gap that is toowide, or damage to toothwheels on the drive axle.

1-7-12-7-14-7-1

Right Rear Wheel

1-7-2

2-7-24-7-2 Left Rear Wheel Sensor circuit failure ondrive axle.

Check sensor, sensor cableand cable connections.1-7-3

2-7-34-7-3

Right Rear Wheel

1-7-42-7-44-7-4

Left Rear Wheel

Drive axle sensor outof adjustment.

Adjust sensors on drive axle.Check for differences betweensteer and drive tire sizes.1-7-5

2-7-54-7-5

Right Rear Wheel

* First digit of Blink Code identifies system configuration: 1 = 6S/6M, 2 = 4S/4M, 4 = 6S/4M.


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1-8-32-8-34-8-3

N/AImproperly wired J1922 EngineData Link. Short circuit to poweror ground, or open circuit.

Check J1922 Engine Data Link,cable and connections.

1-8-52-8-54-8-5

N/A

Improperly wired J1922 EngineData Link. Short circuit to poweror ground, open circuit,wires switched.

Check J1922 Engine Data Link,cable and connections.

1-8-72-8-74-8-7

N/A

Message error detected in J1922Engine Data Link.

Erase fault from ECU memory.No other action required.1-8-9

2-8-94-8-9

N/A

1-8-102-8-104-8-10

Right Front Wheel

Short circuit in steering axle ABSvalve-to-ground connection.

Check ABS valve and cable.Replace as required.1-8-11

2-8-114-8-11

Left Front Wheel

1-8-122-8-124-8-12

Right Front Wheel

Open circuit in steering axle ABSvalve or cable.


2-8-134-8-13

Left Front Wheel

1-8-142-8-144-8-14

Right Front Wheel

Short circuit in steering axle ABSvalve-to-ground connection.


2-8-154-8-15

Left Front Wheel

1-9-02-9-04-9-0

Right Front Wheel

Open circuit in steering axle ABSvalve or cable.


2-9-14-9-1

Left Front Wheel

1-9-22-9-24-9-2

Left Rear Wheel

Short circuit to ground in driveaxle ABS valve or cable.


2-9-34-9-3

Right Rear Wheel


Fault Code




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1-9-42-9-44-9-4

Left Rear Wheel

Open circuit in drive axle ABSvalve or cable.


2-9-54-9-5

Right Rear Wheel

1-9-62-9-64-9-6

Left Rear Wheel

Short circuit to ground in driveaxle ABS valve or cable.


2-9-74-9-7

Right Rear Wheel

1-9-82-9-84-9-8

Left Rear Wheel

Open circuit in drive axle ABSvalve or cable.


2-9-94-9-9

Right Rear Wheel

1-10-22-10-24-10-2

Left Rear Wheel

Short circuit in ATC valve toground connection.

Check ATC valve and cable.Replace as required.1-10-3

2-10-34-10-3

Right Rear Wheel

1-10-42-10-44-10-4

Left Rear Wheel

Open circuit in ATC valveor cable.


2-10-54-10-5

Right Rear Wheel

1-10-72-10-74-10-7

N/AShort circuit in wiring or relaythat controls engine brake.

Check engine brake relay andwiring to relay coil.

1-10-82-10-84-10-8

Left Rear WheelExcessive drive axle wheelspin caused by driver or

dynamometer.

Check steer axle sensor gap.

Erase fault from ECU memory.1-10-92-10-94-10-9

Right Rear Wheel

1-11-122-11-124-11-12

Right Front WheelShort circuit between steeringaxle ABS valve and powersupply connection.


2-11-134-11-13

Left Front Wheel


Fault Code




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1-11-142-11-144-11-14

Left Rear WheelShort circuit between drive axleABS valve and power supplyconnection.


2-11-154-11-15

Right Rear Wheel

1-12-22-12-24-12-2

Left Rear Wheel

Short circuit between ATC valveand power supply connection.


2-12-34-12-3

Right Rear Wheel

1-12-42-12-44-12-4

N/AShort circuit between pin 12 ofABS ECU and power supplyconnection.

Check ECU harness.

1-12-72-12-74-12-7

N/AShort circuit between enginebrake and ground connection.

Check engine brake relay.

1-12-82-12-84-12-8

Right Front Wheel

Short circuit between steeringaxle ABS valve and battery.


2-12-94-12-9

Left Front Wheel

1-12-102-12-104-12-10

Left Rear Wheel

Short circuit between steeringaxle ABS valve and battery.


2-12-114-12-11

Right Rear Wheel

1-12-142-12-144-12-14

Left Rear Wheel

Short circuit between steeringaxle ATC valve and battery.


2-12-154-12-15

Right Rear Wheel

1-13-02-13-04-13-0

N/AShort circuit between pin 12 ofABS ECU and battery.

Check ECU harness.

1-13-42-13-44-13-4

Voltage Relay 1

Diagonal valve relay notoperating correctly.

Check diagonal valve relay.1-13-52-13-54-13-5

Voltage Relay 2


Fault Code




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Page 16

Table B Additional 6S/6M or 6S/4M Blink Codes: 4 = 6S/4M, 1 = 6S/6M

1-13-82-13-84-13-8

Voltage Relay 1

Power supply voltage too high. Repair vehicle power supply.1-13-92-13-94-13-9

Voltage Relay 2

Fault Code

Cause SolutionBlink Code Axle 3Left Right

1-7-8

4-7-8

1-7-9

4-7-9

Erratic wheel speed fromthird axle.

Check for loose wheel bearings, faulty sensorwiring connections, excessive hub runout,sensor gap that is too wide or damage to toothwheels on third axle.

1-7-10

4-7-10

1-7-11

4-7-11

Sensor circuit failure onthird axle.

Check sensor, sensor cable and cableconnections.

1-7-12

4-7-12

1-7-13

4-7-13

Third axle sensor out ofadjustment.

Adjust sensors on third axle. Check fordifferences between steer and rear tire sizes.

1-9-10 1-9-11 Short circuit to ground in thirdaxle ABS valve or cable. Check ABS valve and cable. Replace as required.

1-9-12 1-9-13Open circuit in third axle ABSvalve or cable.

Check ABS valve and cable. Replace as required.

1-9-14 1-9-15Short circuit to ground in thirdaxle ABS valve or cable.


1-10-0 1-10-1Open circuit in third axle ABSvalve or cable.


1-12-0 1-12-1Short circuit in connectionbetween third axle ABS valveand battery.


1-12-12 1-12-13Short circuit in connectionbetween third axle ABS valveand battery.



Fault Code




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TestingThe locations of sensors and valves are illustrated in Figures3.43.9. Most vehicles with spring suspensionhave sensors on forward-rear axle. Most vehicles with air suspension have sensors on rear-rear axle.

Liftable axles are always the third axle with ABS.

Figure 3.4

Figure 3.5

Figure 3.6


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Liftable axles are always the third axle with ABS.

Figure 3.7

Figure 3.8

Figure 3.9


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Optional Test Equipment

WARNINGS

Exhaust gas contains poison. When testing

a vehicle with the engine running, test in awell-ventilated area or route the exhausthose outside

To avoid serious personal injury, keep away,and keep test equipment away, from all moving orhot engine parts.

NOTES

Refer to, and follow, the vehicle manufacturer'sWarnings, Cautions, and Service Procedures.

Unless otherwise directed, set the parking brakeand place the gear selector in NEUTRAL

(manual transmission) or PARK (automatictransmission).

Meritor WABCO Test Adaptor

For use with cab-mounted ECUs only.

CAUTIONWhen troubleshooting or testing the system at themain connector, be careful not to damage theelectrical sockets.

Use the Meritor WABCO test adaptor to measure

the resistance across the harness pins.

When a test involves testing the cable harness, usethe diagram in Figure 3.10 to identify pin locationson the 35-pin connector.

Volt-Ohm Meter (VOM)

The receptacles in the test adaptor accept thetips of standard VOM cables. These tips areapproximately 0.080-inch diameter (2 mm). Use agood quality digital or analog VOM.

A VOM with automatic polarity sensing isrecommended. This eliminates worry over polarityof the meter leads during voltage measurements.

Component Tests

Component tests for tractor, truck, and busapplications are:

Vehicle voltages

Sensors

ABS modulator valves

ATC valves

ABS/ATC lamps

ABS/ATC switches

Testing Procedure

To use the Meritor WABCO test adaptor:

1. Determine the failure code and meaning (seeBlink Code Diagnostic Charts).

2. Turn vehicle ignition OFF.

3. Disconnect the 35-pin harness connector fromthe ECU.

4. Insert the test adaptor into the 35-pinharness connector.

5. Check the following table to determine whichadaptor pins to test with the VOM.

6. Set the VOM to the appropriate scale.

7. Take measurement and write it down.

8. Compare measurement with the desiredmeasurement value listed in Table 1 TestAdaptor Measurement Checks.

9. Repair or replace wiring or componentas necessary.

10. Disconnect the test adaptor from the harnessand reconnect the harness to the ECU.

11. Make sure the ABS is functional; road test thevehicle if necessary.

Figure 3.10


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Page 20

Table 1 Test Adaptor Measurement Checks

CAUTIONThe following tests could damage the measuring

instruments or the ABS and/or ATC valves beingtested. If you do not know how to use a VOM, donot conduct these tests.

If the VOM is not connected properly, damage tothe meter could result.

Valves should not be left connected to power(pin 9) for more than 10 seconds or the valve maybe damaged.

Adhere to all safety warnings and cautions (seeMeritor WABCO Test Adaptor) when usingthe test adaptor. Always perform the tests inTable 1 before attempting the Valve FunctionTests in Table 2.

Test orMeasurement

VOM Setting(Test AdaptorPins)

OtherAction

VehicleIgnition

(Record)ActualMeasurement

DesiredMeasurement

Possible Causes ofMalfunction

Voltage to ECU Volts DC+9 & 27

OFFON

0.0 volts11.0-15.0 volts

Constant power to ECU Blown fuse Power to ECU interrupted

Valve RelayVoltage

Volts DCVR1+1 & 27

VR2+19 & 27

OFF 0.0 volts0.0 volts

VR1 or VR2 relay contactssticking

Warning LightWiring

Ohms26 & 9

OFF 2-50 ohms(typical)

Bulb/LED Wiring to warning light

interrupted ATC/diagnostic light wiring

ATC/DiagnosticLight Wiring

Ohms3 & 9

OFF 2-50 ohms(typical)

Bulb/LED Wiring to ATC/diagnostic

light interrupted

DiagnosticSwitch Wiring

Ohms14 & 27

Press/togglediag. switch

OFF 0-2 ohms Switch Wiring to switch is

interrupted

Speed SensorResistance

OhmsLF 15 & 32RF 17 & 34LR 18 & 35

RR 16 & 33

OFF 700-3000 ohms Broken wire between ECUand sensor

Sensor connector Defective sensor

Speed SensorResistance toGround

OhmsLF 15 & 27RF 17 & 27LR 18 & 27RR 16 & 27

OFF > 30K ohms Shorted sensor wire Chafed/cut sensor cable Defective sensor

Speed SensorAdjustment

Volts ACLF 15 & 32RF 17 & 34LR 18 & 35RR 16 & 33

Turn wheelby hand at30 RPM(2 sec./rev.)

OFF > 0.200 VAC No reading

Sensor wire broken Sensor wire shorted

Sensor gap too large

Large variation

Excessive tone ringrunout

Tone ring damaged Excessive wheel

bearing end play

ABS Valve CoilResistance

OhmsLF In 23 & 27Exh 24 & 27

RF In 6 & 27Exh 7 & 27

LR In 21 & 27Exh 22 & 27

RR In 4 & 27Exh 5 & 27

OFF 4-8 ohms4-8 ohms

Wiring between ECU andvalve interrupted

Ground lead to valveinterrupted

Shorted valve coil

ATC Valve CoilResistance

OhmsLR 2 & 27RR 20 & 27

OFF 8-14 ohms8-14 ohms

Wiring between ECU andvalve interrupted

Ground lead to valveinterrupted

Shorted valve coil


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Table 2 ABS and ATC Valve Function Tests

CAUTIONThe word TOUCH means connect the appropriate

lead to pin 9 only when ready to observe the results.Conduct the ABS and ATC valve Function Testsonly if the Measurement Checks in Table 1 yieldedinconclusive results. This could occur because ofimproper plumbing to the ABS or ATC valves orbecause the wiring to the ABS valves has the inletand exhaust portions of the solenoid interchanged.

In either case, the ECU may not detect the errorand it will be necessary to manually activate thevalves to confirm correct function.

Adhere to the cautions listed for Table 1 whenperforming the following tests.

Adhere to all safety warnings and cautions (seeMeritor WABCO Test Adaptor) when using thetest adaptor.

Always perform the tests in Table 1 beforeattempting the Valve Function Tests in Table 2.

Test

VOM settingTest AdaptorPins

VehicleIgnition Additional Action Desired Results

Possible Causes ofMalfunction

ABSValveFunction

10 Amps

LF: Exh (+) to 9

ON Apply and maintainbrake application TOUCH () to 24 -----> Release brake

Left front chamber exhaustscontinuously

Wiring to valve is

interchanged Valve plumbing is

incorrect Valve defective

In (+) to 9 TOUCH () to 23 Apply brake------------> No pressure build-up in LF

chamber

10 Amps

RF: Exh (+) to 9ON Apply and maintain

brake application TOUCH () to 7 -------> Release brake

Right front chamber exhaustscontinuously

In (+) to 9 TOUCH () to 6 Apply brake------------> No pressure build-up in RF

chamber

10 Amps

LR: Exh (+) to 9ON Apply and maintain

brake application TOUCH () to 22 -----> Release brake

Left rear chamber(s) exhaustscontinuously

In (+) to 9 TOUCH () to 21 Apply brake------------> No pressure build-up in LR

chamber(s)

10 Amps

RR: Exh (+) to 9ON Apply and maintain

brake application TOUCH () to 5 -------> Release brake

Right rear chamber(s)exhausts continuously

In (+) to 9 TOUCH () to 4 Apply brake------------> No pressure build-up in RRchamber(s)

ATCValveFunction

10 Amps

LR (+) to 9

RR (+) to 9

ON TOUCH () to 2

TOUCH () to 20

Pressure build-up in LRchamber(s)

Pressure build-up in RRchamber(s)

Plumbing to ATCvalve blocked,incorrect

Valve defective


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Page 22

Final Test for a TractorEquipped with ABS

NOTETurn the blink code switch to the OFF position.Complete the following test.

For a Tractor Equipped with ABS:

1. Check that the cab harness is attached tothe ECU.

2. Start the engine.

3. Increase vehicle speed. At about 4 mph(6 km/h), the tractor warning light must to out.

NOTES

If the tractor warning light continues tostay on, check blink codes, all componentsand connections.

When failures cannot be repaired, contactyour Meritor District Service Manager at800-535-5560 in the U.S. and Canada.

MPSI Pro-Link 9000

Use the Pro-Link 9000 to:

Diagnose System Faults on ABS and ABS/ATCsystems with C2 and C3 ECUs. (May be used in

place of blink code diagnostic procedures.) Perform component measurement and

function tests.

NOTEPro-Linkscreens identify faults as existingor stored. See Blink Code Definitionsfor definitions.

Component Tests

Components that may be tested with thePro-Link 9000 are:

NOTEAdhere to all safety Warnings and Cautions (seeMeritor WABCO Test Adaptor).

Diagnostic and Testing Procedure

1. Locate the 6-pin connector in the vehicle cab.Gather together everything you need duringthe test.

Pro-Link

9000 Meritor WABCO test cartridge

6-pin connector

2. Slide the Meritor WABCO cartridge into thePro-Link keypad until connection is tight.Figure 3.11.

3. Chock the wheels, apply the parking brake, andmake sure ignition power is off.

WARNINGBlock the wheels to prevent the vehicle frommoving. Support the vehicle with safety satnds.Do not work under a vehicle supported only by

jacks. Jacks can slip and fall over. Serious personalinjury can result.

4. Connect the Pro-Link to the 6-pin connectoron the ECU.

5. Turn the ignition to the ON/RUN position.

6. Check the Pro-Link screen to make sure itpowers up.

If the Pro-Link does not power up or if thescreen indicates NO DATA RECEIVED:

Check connections.

Make sure the cartridge is properlyconnected to the Pro-Link keypad.

Verify 12 volts DC power and ground at theconnector and ABS ECU.

Check the fuse panel for a blown fuse.

Check for proper wiring in the diagnosticconnector.

7. Refer to the Pro-Link manual for completediagnostic and testing instructions.

Vehicle Voltages

ABS Modulator Valves

ATC Valves

ABS/ATC Lamps

Sensors

Engine Datalink

Retarder Relay

Retarder Datalink

ABS/ATC Switches

Figure 3.11


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Page 23


Testing and Diagnostic Screens

NOTEThe menu selections for the Pro-Linkare described

below. Refer to the Pro-Link

manual for completetesting instructions.

Vehicle Voltages

Monitors the two voltage signals poweringthe ECU.

ABS Modulator Valves (Two Tests)

Choose from four or six valves:

For 4S/4M or 6S/4M systems choose

L Front Valve L 2nd Axle Valve

R Front Valve R 2nd Axle Valve

For 6S/6M there are two additional valves:

R Third Axle Valve L Third Axle Valve

Exercises ABS modulator valves one at a time.

With brake applied:

Selected ABS modulator valve will showdecreased air chamber pressure.

Test has four cycles, each with three decreasesof pressure.

Cycles are separated by a pause.

Selected ABS modulator valve is cycled 15 times

A faint clicking of the internal solenoid is heard 15times during this test.

No change in air chamber pressure should occur.

ATC Valves

Exercises the left and right rear ATC valves,

one at a time. Valve is cycled 15 times for a period of

six seconds.

ABS/ATC Lamps

Monitors the ABS and ATC indicator lamps on theinstrument panel.

Figure 3.12

Figure 3.13

Figure 3.14

Figure 3.15

Figure 3.16


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Page 24

Sensors

Rotate wheel:

Monitors the inputs to the ECU from the wheelsensors, one at a time.

Engine Datalink (ATC vehicles only)

Reduces engine torque to verify proper wiring.

Retarder Relay

Verifies relay is functioning properly (a clickshould be heard).

Checks wiring connections.

Retarder Datalink

Checks wiring connections.

ABS/ATC Switches

Checks status of ABS and ATC/Deep Snow-Mudswitches on the instrument panel.

Testing ComponentsIf the blink codes or MPSI Pro-Link indicate aproblem with an ABS or ABS/ATC component,always check the wiring or connections beforereplacing the component. In your preliminarycheck look for:

Loose connections

Corrosion

Breakage

See Meritor WABCO Test Adaptor in this sectionfor information. The adaptor makes checkingresistance across the harness pins easier.

CAUTIONWhen troubleshooting and testing the ABSsystem at the main ECU connector, be carefulnot to damage the electrical sockets on theECU connector.

Figure 3.17

Figure 3.18

Figure 3.19

Figure 3.20

Figure 3.21


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Page 25


Ignition Voltage

Voltage must be between 11.0 and 15.0 v. Measurevoltage between pin 9 and pin 27 on cab mountsystems and between 10 and 12 on the 19-pinconnector on frame-mounted ECUs with ignition on.

Sensor Resistance

The sensor circuit resistance must be700-3000 ohms. Resistance can be measured atthe sensor connector when it is removed fromthe ECU, or right at the sensor when the extensioncable is removed.

Sensor Adjustment

NOTE

On the steering axle the sensor is accessible on thein-board side of the steering knuckle.

On the drive axle the wheel and drum assemblymust be pulled to gain access to the sensor.

Gently push the sensor in toward the tooth wheeluntil it contacts the tooth wheel.

ABS Valve

The resistance across each valve solenoid coilterminal and the ground on the ABS valveconnector must be 4.0 to 8.0 ohms. Figure 3.22.

When the resistance is greater than 8.0 ohms,clean the electrical contacts in the solenoid.

Check the resistance again.

To check the cable and the ABS valve as one unit,

measure across the pins on the ECU connectorof the cab harness. Reference the diagram of thesystem you are testing for pin numbers (seeSection 5, "Wiring").

ATC Valve

The resistance across the two electrical terminalson the ATC valve must be 8.0 to 14.0 ohms.Figure 3.23.

If the resistance is greater than 14.0 ohms, cleanthe electrical contacts on the solenoid.

Check the resistance again.

To check the cable and ATC valve as one unit,measure the resistance across the pins:

Use the connector at the connection point ofthe ECU for frame mounts

Use the Meritor WABCO test adaptor forcab mounts

Reference the diagram of the system you aretesting for pin numbers (see Section 5, "Wiring")

Figure 3.22

1 Ground Terminal2 Exhaust Solenoid3 Inlet Solenoid

Figure 3.23


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Page 26

Dynamometer Testing Vehicleswith ATC

WARNING

Failure to disable the ATC before dynamometertesting could result in serious personal injury anddamage to the vehicle.

Vehicles with the ATC option must have the ABSsystem power disabled to test the vehicle on adynamometer. The method requires removing theABS circuit breaker/fuse or removing the ECUmain connector. Disconnect connector or breakerwith ignition in the OFF position.

Tire Size Range

CAUTIONFor proper ABS/ATC operation with the standardElectronic Control Unit (ECU), front and reartire sizes must be within 5% of each other.When this tire size range is exceeded withoutelectronically modifying the ECU, the systemperformance can be affected and the warning lampcan illuminate. Call Meritor WABCO at800/535-5560 when you plan a tire size differencegreater than 5%.

Calculate tire size with the following equation:

% Difference = (RPM Steer RPM Drive 1) x 100

RPM = tire revolutions per mile


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Section 4Removal & Installation

Section 4Removal&Install ation

Component Removaland Installation

WARNINGTo prevent serious eye injury, always wear safeeye protection when you perform vehiclemaintenance or service.

CAUTIONUse the following procedures to avoid damage tothe electrical system and ABS/ATC components.

When welding on an ABS- or ABS/ATC-equippedvehicle is necessary, disconnect power and groundleads from the ECU.

Sensors

Wheel Speed Sensor Removal Front Axle

To remove the sensor from the front axle:

1. Put blocks under the rear tires to stop thevehicle from moving. Apply the parking brake.



2. Raise the front tires off the ground. Put safetystands under the axle.

3. Remove the sensor from the steering knuckle.Use a twisting motion if necessary. Do not pullon the cable.Figure 4.1.

4. Disconnect the fasteners that hold the sensorcable to other components.

5. Disconnect the sensor cable from thechassis harness.

See Sensor Resistance and SensorAdjustment for additional sensor information.

Wheel Speed Sensor Installation Front Axle

To replace the sensor in the front axle:

1. Connect the sensor cable to the chassis harness

2. Install the fasteners used to hold the sensorcable in place.

3. Apply a mineral oil-based lubricant that containsmolydisulfide to the sensor spring clip and tothe body of the sensor. The lubricant shouldhave excellent anti-corrosion and adhesioncharacteristics, and be capable of continuousfunction in a temperature range of 40 to 300F(40 to 150C).

4. Install the sensor spring clip. Make sure theflange stops are on the inboard side ofthe vehicle.

5. Push the sensor spring clip into the bushing inthe steering knuckle until the clip stops.

6. Push the sensor completely into the sensorspring clip until it contacts the tooth wheel.

7. Remove the blocks and safety stands.

Wheel Speed Sensor Removal Rear Axle

To remove the sensor from the rear axle:



1. Put blocks under the front tires to stop thevehicle from moving.

Figure 4.1


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2. Raise the rear tire off the ground. Put safetystands under the axle.

3. Release the parking brake and back off theslack adjuster to release the brake shoes.

4. Remove the wheel and tire assembly fromthe axle.

5. Remove the brake drum.

6. Remove the sensor from the mounting block inthe axle housing. Use a twisting motion ifnecessary. Do not pull on the cable.

7. Remove the sensor spring clip from themounting block.

8. Disconnect the fasteners that hold thesensor cable and the hose clamp toother components.

9. Disconnect the sensor cable from thechassis harness.

Wheel Speed Sensor Installation Rear Axle

1. Apply a mineral oil-based lubricant thatcontains molydisulfide to the sensor springclip and to the body of the sensor. Thelubricant should have excellent anti-corrosionand adhesion characteristics, and be capable ofcontinuous function in a temperature range of40 to 300F (40 to 150C).

2. Install the sensor spring clip. Make sure the

flange stops are on the inboard side ofthe vehicle.

3. Push the sensor spring clip into the mountingblock until it stops.

4. Push the sensor completely into the sensorspring clip until it contacts the tooth wheel.Figure 4.2.

5. Insert the sensor cable through the hole in thespider and axle housing flange. Route thecable to the frame rail. Be sure to route thecables in a way that will prevent pinching orchafing and will allow sufficient movement for

suspension travel.

6. Connect the sensor cable to thechassis harness.

7. Install the fasteners that hold the sensorcable in place.

8. Install the brake drum on the wheel hub.9. Complete the installation per vehicle

manufacturer's manual.

Valves

ABS Modulator Valve Removal

1. Turn ignition switch to the OFF position, applyparking brake.

2. Put blocks under the front and rear tires to stopthe vehicle from moving.



3. If necessary, raise the vehicle off the groundand put safety stands under the axle.

4. Disconnect the wiring connector from theABS valve.

Figure 4.2

1 Spring Clip2 Sensor Holder3 Spring Clip Tab4 Sensor


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Page 29


5. Disconnect the air lines from Ports 1 (airsupply) and 2 (air discharge) of the ABS valve.Figure 4.3.

6. Remove the two mounting capscrews andnuts.

7. Remove the ABS valve.

ABS Modulator Valve Installation

CAUTIONMoisture can affect the performance of allABS/ATC systems, as well as the standard brakingsystem. Moisture in air lines can cause air lines tofreeze in cold weather.

Installation Guidelines:

Use thread sealant correctly to avoid air lineleaks in pneumatic connections.

Follow supplier recommendations.

To install the ABS modulator valve:

1. Install the ABS valve with two mountingcapscrews and nuts. Tighten the capscrews perthe manufacturer's recommendation.

2. Connect the line to the brake chambers to port2 of the ABS valve. Connect the air supply lineto port 1 of the ABS valve.

3. Connect the wiring connector to the ABS valve.

4. Remove the blocks and stands.

ATC Valve Removal

1. Turn ignition switch to the OFF position, applyparking brake.



2. Put blocks under the front and rear tires to stopthe vehicle from moving.

3. If necessary, raise the vehicle off the groundand put safety stands under the axle.

4. Disconnect the wiring from the ATC valve.

5. To relieve line pressure, bleed the air from the

appropriate supply tank.

6. Disconnect the air lines from Ports 1 (airsupply) and 2 (air discharge) of the ATC valve.

7. Remove the two mounting capscrews andnuts.

8. Remove the ATC valve.

ATC Valve Installation

Installation Guidelines:

Use thread sealant correctly to avoid air line

leaks in pneumatic connections.

Follow supplier recommendations.

To install the ATC valve:

1. Install the ATC valve with two mountingcapscrews and nuts. Tighten the capscrews perthe manufacturer's recommendation.

2. Connect the line from the double check valve toport 2 of the ATC valve. Connect the air supplyline to port 1 of the ATC valve.

3. Connect the harness connector to theATC valve.

4. Remove the blocks and stands.

ABS Valve Package

If you are servicing a vehicle with an ABS ValvePackage, you will need TP-95144, Servicing theABS Valve Package. Contact Meritor WABCO at800-535-5560 for this literature.

Figure 4.3


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Section 5Wiring

Page 30

Section 5Wiring

WiringThis section contains ABS wiring diagrams and connector pin callouts. If you have any questions, pleasecontact Meritor Customer Service at 800-535-5560.

Figure 5.1


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Page 31

Section 5Wiring

ABS/ATC Wiring Schematic

Cab-Mounted ECU

Figure 5.2


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Section 5Wiring

Page 32


Frame-Mounted ECU Left/Right Harness Configuration

Figure 5.3


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Page 33

Section 5Wiring

Figure 5.4


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Section 5Wiring

Page 34


Frame-Mounted ECU Front/Rear Harness Configuration

Figure 5.5


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Page 35

Section 5Wiring

Figure 5.6


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Section 5Wiring

Page 36

Front/Rear Configurations

Figure 5.7


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Page 37

Section 5Wiring

Left/Right Configurations

Figure 5.8


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Section 5Wiring

Page 38

In-Cab ECU Wiring Diagram

Figure 5.9


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Page 39

Section 5Wiring

In-Cab ECU Wiring Diagram

Figure 5.10


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Information contained in this publication was in effect at the time the publication was approved for

printing and is subject to change without notice or liability. Meritor WABCO reserves the right to

revise the information presented or discontinue the production of parts described at any time.

Copyright Maintenance Manual No. 28

Meritor WABCO Printed in the USA Revised 4/98

Meritor WABCO

Vehicle Control Systems

2135 West Maple Road

Troy, MI 48084 U.S.A.

800-535-5560www.meritorauto.com

1998

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