Brake System Preventive Maintenance
– 158 – Y53-6008
Medium Duty (R10/06)
• During wheel balancing, dyno testing, or any time the
ignition is on with part of the ABS disconnected, a failure
code will be recorded. Consult with your Peterbilt Dealer
or Authorized Service Center for information on clearing
the failure code.
If, due to operating conditions, a brake application causes
either wheel on the same axle to begin skidding, wheel
speed sensors immediately signal the anti-lock controller in
the modulator assembly. The controller responds instantly by
signaling the solenoids in the modulator which activate the air
valves, reducing application pressure as needed to prevent
the wheels from locking up. If this over-riding correction is
effective, application pressure is allowed to build up to the
original input.
Any malfunction of the anti-lock system on one or more axles
will cause the system to fail-safe, and the panel-mounted
amber warning light will come on, indicating both a malfunc-
tion, and automatic shut-down of the system. If the founda-
tion brake system is intact, the service brakes will continue to
function normally, but without benefit of the anti-lock feature.
NOTE: If one wheel on any driven axle continues to
slip or spin for approximately 4 seconds, this will
cause the anti-lock controller for that axle to go into
the fail-safe mode, and the warning light will give a
shutdown signal.
•In this case, the anti-lock system can be turned
back on, and the warning light extinguished, by turn-
ing the key switch OFF and ON, after the vehicle has
been brought to a full stop. When the key switch is
turned back on, the warning light will illuminate and
remain on for 3 to 5 seconds. This is a built-in func-
tion test of the warning light.
WARNING! Do not attempt to recycle the anti-
lock system by turning the keyswitch OFF and
ON until the vehicle has been brought to a full
stop and the parking brakes set. Failure to do so
could adversely affect steering and braking con-
trol, and may result in loss of vehicle control and
an injury accident.
