Anti-Lock Braking Systems (ABS) for Trucks ... - Meritor WABCO

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Section 1IntroductionSection 1IntroductionAbout This ManualThis manual contains service, troubleshooting,and repair information for the Meritor WABCOAnti-Lock Braking System (ABS) and ABS withAutomatic 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 IdentificationECU Mounting LocationsThe Electronic Control Unit (ECU) may be mountedin the cab or on the frame of the vehicle.ABS ConfigurationThe 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", Figures 3.4–3.9.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 ChartVehicleModel YearManufacturerECUMountingABS Configuration Tire Sizes OptionalATCVIN Cab Frame 4S/4M 6S/4M 6S/6M Front Rear Y NPage 3
Section 1IntroductionABS ComponentsFigure 1.3Figure 1.11 Cab-Mounted2 Frame-MountedThe 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.A sensor is installed so that its end is against thetooth wheel. The sensor continuously sends wheelspeed information to the ECU. On a four-channelABS, 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.Figure 1.4NOTEDo not open the ECU. Opening the ECU to gainaccess to the internal components will void thewarranty.Figure 1.2The sensor clip holds the sensor in place at thetooth wheel. Figure 1.4.The tooth wheel is mounted on the hub of eachmonitored wheel. Figure 1.2.Page 4
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Anti-Lock Braking Systems (ABS) for Trucks ... - Meritor WABCO

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