Navistar WorkStar Series, Operator'S Manual

Page: 166 / 258

Operation
is imminent. The standard air brake system controls normal
braking when the ABS is not engaged.
ABS Operation
WARNING
If the ABS warning indicator comes on, stopping
distances may increase under certain braking
conditions.
Have the ABS system repaired
immediately. Take every precaution to prevent
wheel lockup, which could result in loss of
vehicle
control causing property damage,
personal injury, or death.
The antilock brake system electronically monitors vehicle
wheel speed at all times and only engages when wheel lock is
imminent. The standard hydraulic brake system controls normal
braking when the ABS is not engaged.
ABS requires no changes in driving practices. For the best
stopping performance with or without ABS, modulate - do
not pump - the brake pedal until the vehicle slows to desired
speed or stops. Be aware that ABS on a towing vehicle does
not control brakes on towed vehicles.
Towed vehicles may
or may not have ABS. ABS will prevent lockup of controlled
wheels if you overbrake for existing road conditions. Optimum
vehicle control for existing road conditions will be provided as
a result of the ABS preventing wheel lockup at speeds above
approximately 4 mph (6 km/h). The ABS cannot provide any
better braking and steering capability than the available road
traction will permit.
If the road is slippery it will take longer
to stop than on a dry road. Steering maneuverability will be
similarly limited. Vehicle speed must be reduced to compensate
for the extended time and distance required to stop or slow the
vehicle on slippery roads.
The wheel hubs carry exciter rings used by axle-mounted
sensors to transmit wheel speed information to the ABS
electronic control unit located on the chassis frame. The control
unit monitors and compares all wheel speed inputs to determine
if any wheel(s) is about to lock. If wheel lockup is about to occur,
the control unit commands the appropriate modulator valve to
adjust air pressure delivery to prevent wheel lockup.
ABS Self-Check
A yellow warning indicator on the instrument panel gauge cluster
indicates the antilock system status. The indicator comes on and
the system goes through an ABS self-checkout sequence each
time the ignition is turned on. The system is working normally
when: ignition is turned on, indicator comes on, then flashes
twice and remains on for several seconds before going out.
During the self-checkout, the modulator valves will cycle around
the vehicle twice in the following pattern:
1. Right Front
2. Left Front
3. Right Rear
4. Left Rear
A fault has been detected in the ABS if the indicator does not
come on with ignition, does not flash, fails to go off, or comes on
again at any other time.
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