7 Appendix III — Additional ABS Information
48
Meritor WABCO Maintenance Manual MM-0112 (Revised 07-05)
7 Appendix III — Additional A BS Information
Troubleshooting
Meritor WABCO ABS Valve Package
This troubleshooting information is a reference tool to help identify possible malfunctions of the ABS modulator or relay valves. It does not take
the place of diagnostic tests or other service instructions.
Condition Possible Cause Recommended Action
Air constantly leaks
from exhaust port of
relay valve.
Internal relay valve problem. Replace the relay valve.
Air leaks from exhaust
port of ABS modulator
valve or relay valve
when parking brake is
released.
Parking brake problem.
OR
Anti-compound 2-way check valve problem.
Service the appropriate component.
앫 Refer to manufacturer’s service manual for
instructions.
Rear service brakes
releasing slowly
(brakes dragging).
Kinked air line.
Dirt buildup inside relay valve.
Inspect/repair lines, brakes.
If the condition is not corrected:
앫 Replace the relay valve.
Valves don’t cycle at
power-up.
OR
Indicator lamp comes
on (blink code or
diagnostic tool
indicates electrical
problem with ABS
valve).
Broken wire.
OR
Loose or broken terminal connection.
Corroded connector pins.
OR
Problem with solenoid.
Check the wires and connections.
앫 Make repairs as needed.
If condition is not corrected: Measure
resistance across each valve solenoid coil
terminal and ground on the ABS modulator valve
to ensure 4.0 to 8.0 ohms.
앫 If greater than 8.0 ohms, clean the valve and
repeat the measurement.
— If cleaning does not solve the problem,
replace the ABS modulator valve.
앫 If less than 4.0 ohms, replace the ABS
modulator valve.
ABS valve package
damaged.
Road hazards.
OR
Vehicle damage.
Replace the complete ABS valve package or
individual component as required.
OPEN-STYLE CONNECTOR
GROUND
TERMINAL
EXHAUST
SOLENOID
(BLUE WIRE)
INLET SOLENOID
(BROWN WIRE)
BAYONET-STYLE CONNECTOR
EXHAUST
SOLENOID
(BLUE WIRE)
INLET
SOLENOID
(BROWN WIRE)
GROUND
TERMINAL
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