WARNING LIGHT ILLUMINATES WHEN
VEHICLE IS OPERATED
As the vehicle is driven about 24 km (15 mph) the
antilock warning light should remain "OFF". If the light should
come "ON" and remain on above 24 km (15 mph), a wheel
sensor problem may exist. Excessive spin on one drive wheel
relative to the other on some axles may cause the monitor
light to go "ON". To correct this condition, the ignition switch
must be turned "OFF" and back "ON" to reset the system and
correct the condition.
If wheel spin is not the cause of the light remaining on,
one or more of the sensors could be the problem.
Most common problems found with the sensors are:
Vehicle brake hang-up and slow release of brakes
Loose-wheel bearings causing excessive exciter ring
Insufficient voltage output of sensor or shorted sensor
or sensor wires.
Improper installation of wheel and drum assemblies,
could result in insufficient voltage output.
Do not rock the hub and drum when installing
as the sensor may be pushed in too far. Do
not forget to pull the sensor out to its
maximum outward travel (away from center of
vehicle) prior to installing the hub and drum
assembly to assure that the sensor is properly
Always check the sensor voltage output connector
located at some point on the axle after performing any
maintenance to brakes, wheel bearings or wheel seals.
A volt-ohm meter can be used for sensor voltage
output check at sensor connector by spinning the wheel
about one revolution every two seconds. Voltage
should not be lower than .3 volt.
IGNITION CYCLE ANTILOCK SYSTEM
To ignition cycle the antilock system, turn the ignition
switch "ON" to "OFF" several times prior to starting the
ignition cycle check. Then with at least 552 kPa (80 psi) air in
system, apply the brakes and turn the ignition switch to "ON"
position. This allows all air valves to exhaust a small amount
of air. Continue to turn the ignition switch "ON" to "OFF" with
applied until all computer modules and air control valves have
been checked. An assistant will be required to listen for the
exhaust of air at each axle air control valve.
A regular schedule for periodic cleaning, lubrication,
adjustment and inspection should be established, based on
the type of vehicle operation. It is difficult to predetermine an
exact maintenance interval (time or mileage) since vehicles
will be used in a wide variety of operational applications and
Periodic checking of push rod travel or brake
adjustment is essential for good braking. Push rod travel
should be checked every 3,000 km (2,000 miles) to determine
if adjustment is necessary. Push rod travel should be kept at
a minimum without brakes dragging.
Inspect brake lining every 19,000 km (12,000 miles) or
every 12 months; whichever occurs first. When brake lining
or blocks are worn to within 1.6 mm (1/16") of rivets, brake
lining must be replaced.
performed by qualified service personnel and must be in
Do not back off front brakes so that they are not as
aggressive, letting the rear brakes do all the stopping of the
vehicle. Do not overlook the brakes on the trailer either.
Brake balance on trucks and tractor trailers is essential for
good braking and minimize cycling of the antilock.
Too much lining-to-drum clearance will require more air
to be delivered to each of the brake chambers since a longer
stroke of the chamber is required. Improper brake adjustment
on an axle (one brake group adjusted properly and the brake
group on opposite side of vehicle backed off) will result in an
antilock cycle since one brake group will tend to lock up or
slow down more rapidly than the other. This cycling of the
antilock will tend to increase the stopping distance of a