mm28 Anti Lock Braking Systems ABS for Trucks, Tractors, and Buses C Version

3 Troubleshooting

Tire Size Range

ATC Valve The resistance across the two electrical terminals on the ATC valve must be 8 to 14 ohms. Figure 3.23.

CAUTION For proper ABS/ATC operation with the standard Electronic Control Unit (ECU), front and rear tire sizes must be within ± 5% of each other. When this tire size range is exceeded without electronically modifying the ECU, the system performance can be affected and the warning lamp can illuminate. Call WABCO North America Customer Care at 855-228-3203 when you plan a tire size difference greater than 5%.

Figure 3.23

Calculate tire size with the following equation:

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

1000441a

RPM = tire revolutions per mile

Figure 3.23

If the resistance is greater than 14 ohms, clean the 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 of the ECU for frame mounts — Use the WABCO test adaptor for cab mounts Reference the diagram of the system you are testing for pin numbers in Section 5. Dynamometer Testing Vehicles with ATC WARNING Failure to disable the ATC before dynamometer testing could result in serious personal injury and damage to the vehicle. Vehicles with the ATC option must have the ABS system power disabled to test the vehicle on a dynamometer. The method requires removing the ABS circuit breaker/fuse or removing the ECU main connector. Disconnect connector or breaker with ignition in the OFF position.

28 WABCO Maintenance Manual MM-28 (Revised 03.2020)