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

3 Troubleshooting

9. Repair or replace the wiring or component as necessary. 10. Disconnect the test adaptor from the harness and reconnect the harness to the ECU.

11. Verify that the ABS is functional. Road test the vehicle if necessary.

Table F: Test Adaptor Measurement Checks

VOM Setting (Test Adaptor Pins)

Test or Measurement

Vehicle Ignition

(Record) Actual Measurement

Desired Measurement 0.0 volts 11.0-15.0 volts

Possible Causes of Malfunction

Other Action

Volts DC +9 & − 27

Voltage to ECU

OFF ON

Constant

power to ECU

Blown fuse Power to ECU interrupted

Volts DC VR1+1 & − 27 VR2+19 & − 27

Valve Relay Voltage

OFF

0.0 volts 0.0 volts

VR1 or VR2

relay contacts sticking

Ohms 26 & 9

Warning Light Wiring

OFF

2-50 ohms (typical)

Bulb/LED Wiring to

warning light interrupted ATC/diagnostic light wiring Bulb/LED Wiring to ATC/ diagnostic light interrupted

Ohms 3 & 9

ATC/Diagnostic Light Wiring

OFF

2-50 ohms (typical)

Ohms 14 & 27

Diagnostic Switch Wiring

Press/toggle diag. switch

OFF

0-2 ohms

Switch Wiring to switch is

interrupted

20 WABCO Maintenance Manual MM-28 (Revised 03.2020)