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PROBLEM
ALL BRAKES DO NOT RELEASE
INSUFFICIENT BRAKES
BRAKES GRABBING
EXCESSIVE LEAKAGE WITH BRAKES
RELEASED
EXCESSIVE LEAKAGE WITH BRAKES
APPLIED
EXCESSIVE LEAKAGE WITH
EMERGENCY SYSTEM ONLY
APPLIED - NO LEAKAGE WITH
NORMAL BRAKING
EXCESSIVE WATER PRESENT IN
BRAKE SYSTEM
EXCESSIVE OIL PRESENT IN BRAKE
SYSTEM
BRAKE WILL NOT APPLY PROPERLY
BRAKES WILL NOT APPLY WHEN
EMERGENCY LINE IS
DISCONNECTED
ABS WARNING LIGHT STAYS
ON
TABLE OF CONTENTS
PROBABLE CAUSE
Air system improperly connected to
tractor
Brake valve on tractor is applied
Relay emergency valve in emergency
position
Restricted tubing or line
Defective tractor protection valve
Parking brakes locked
Moisture in air system
Tractor pressure too low
Brakes need adjusting
Brakes need lubricating
Brakes need relining
Low air pressure
Defective relay emergency valve
Brakes overheated
Grease on brake linings
Brake rigging binding
Defective brake valve on tractor
Defective relay emergency valve
Relay emergency valve leaking
Leaking tubing or hose
Relay emergency valve leaking
Leaking brake chamber diaphragm
Call Factory or see qualified Trailer/Brake Technician
Leaking tubing or hose
Defective relay emergency valve
Reservoir not drained often enough
Compressor on tractor passing
excessive oil
Flat spot on cam roller or camshaft
Initial air pressure too low
Defective relay valve
Air line leak
Brake chamber leak
Refer to Rockwell WABCO ABS maintenance manual supplied with semitrailer, for
system function and use of blink code diagnostics.
TROUBLESHOOTING GUIDE
SOLUTION
Tighten or adjust connections.
Release brake
Check line pressure and check valve
Locate restriction and remove
Troubleshoot tractor air system.
Troubleshoot air system
Check air system
Adjust to provide 105 psi min.
(See "Brake
Adjust brakes
Adjustment" on page 4-16.)
Lubricate brakes
Reline brakes
Troubleshoot air system.
Repair or replace.
Stop and allow brakes to cool, locate
cause of overheating.
Reline brakes
Align brakes or replace bent parts.
Repair or replace valve.
Repair or replace valve.
Repair or replace valve
Replace defective part.
Repair or replace valve.
Replace diaphragm.
Replace defective part.
Repair or replace valve.
Drain reservoir daily.
Repair compressor.
Replace and lubricate.
Allow air system to build up to
minimum 90 PSI and stabilize.
Repair or replace valve.
Locate leak and repair.
Locate leak and repair or replace.
5-5
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