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

3 Troubleshooting

Table G: ABS and ATC Valve Function Tests

VOM setting Test Adaptor Pins 10 Amps LF: Exh (+) to 9

Vehicle Ignition

Possible Causes of Malfunction

Test

Additional Action

Desired Results

ABS Valve Function

ON

Apply and maintain brake application TOUCH ( − ) to 24  Release brake

Wiring to valve is interchanged Valve plumbing is incorrect Valve defective

Left front chamber exhausts continuously

In (+) to 9

TOUCH ( − ) to 23 Apply brake 

No pressure build-up in LF chamber Right front chamber exhausts continuously

10 Amps RF: Exh (+) to 9

ON

Apply and maintain brake application TOUCH ( − ) to 7  Release brake

In (+) to 9

No pressure build-up in RF chamber

TOUCH ( − ) to 6 Apply brake 

10 Amps LR: Exh (+) to 9

ON

Apply and maintain brake application TOUCH ( − ) to 22  Release brake TOUCH ( − ) to 21 Apply brake  Apply and maintain brake application TOUCH ( − ) to 5  Release brake

Left rear chamber(s) exahusts continuously

In (+) to 9

No pressure build-up in LR chamber(s)

10 Amps RR: Exh (+) to 9

ON

Right rear chamber(s) exhausts continuously

In (+) to 9

TOUCH ( − ) to 4 Apply brake 

No pressure build-up in RR chamber(s)

WABCO Maintenance Manual MM-28 (Revised 03.2020)

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