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

3 Troubleshooting

Ohms LF In 23 & 27 Exh 24 & 27 RF In 6 & 27 Exh 7 & 27 LR In 21 & 27 Exh 22 & 27 RR In 4 & 27 Exh 5 & 27 Ohms LR 2 & 27 RR 20 & 27 VOM Setting (Test Adaptor Pins)

ABS Valve Coil Resistance Test or Measurement

Vehicle Ignition

(Record) Actual Measurement

Desired Measurement

Possible Causes of Malfunction

Other Action

OFF

4-8 ohms 4-8 ohms

Wiring

between ECU and valve interrupted Ground lead to valve interrupted Shorted valve coil between ECU and valve interrupted Ground lead to valve interrupted Shorted valve coil Wiring

ATC Valve Coil Resistance

OFF

8-14 ohms 8-14 ohms

CAUTION The word TOUCH means connect the appropriate lead to pin 9 only when you are ready to observe the results. Conduct the ABS and ATC valve Function Tests only if the measurement checks in Table F yielded inconclusive results. This could occur because of improper plumbing to the ABS or ATC valves or because the wiring to the ABS valves has the inlet and exhaust portions of the solenoid interchanged. In either case, the ECU may not detect the error and it will be necessary to manually activate the valves to confirm correct function. Adhere to the cautions listed for Table F when performing the following tests. Adhere to all safety warnings and cautions in this section when using the test adaptor. Always perform the tests in Table F before attempting the tests in Table G.

22 WABCO Maintenance Manual MM-28 (Revised 03.2020)