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BRAKES - ABS
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OPERATION
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SPECIFICATIONS
TORQUE CHART . . . . . . . . . . . . . . . . . . . . . . 40
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REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
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REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
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DESCRIPTION
The antilock brake system (ABS) is an electroni-
cally operated, three channel brake control system.
The vehicle has Electronic Variable Brake Propor-
tioning (EVBP) designed into the system which elim-
inates the combination/proportioning valve.
The system is designed to prevent wheel lockup
and maintain steering control during braking. Pre-
venting lockup is accomplished by modulating fluid
pressure to the wheel brake units.
The hydraulic system is a three channel design.
The front wheel brakes are controlled individually
and the rear wheel brakes in tandem. The ABS elec-
trical system is separate from other electrical circuits
in the vehicle. A specially programmed controller
antilock brake unit operates the system components.
ABS system major components include:
• Controller Antilock Brakes (CAB)
• Hydraulic Control Unit (HCU)
• Wheel Speed Sensors (WSS)
• ABS Warning Light
BRAKES - ABS
TABLE OF CONTENTS
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page
REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
OPERATION
Battery voltage is supplied to the CAB. The CAB
performs a system initialization procedure at start
up. A check of the ABS motor is performed at 15
miles per hour. Initialization consists of a static and
dynamic self check of system electrical components.
The static and dynamic checks occurs at ignition
start up. During the dynamic check, the CAB briefly
cycles solenoids to verify operation. An audible noise
may be heard during this self check. This noise
should be considered normal. The ABS motor and
pump are then checked at a speed of 15 mile per
hour.
If an ABS component exhibits a fault during ini-
tialization, the CAB illuminates the amber warning
light and registers a fault code in the microprocessor
memory.
The CAB monitors wheel speed sensor inputs con-
tinuously while the vehicle is in motion. However,
the CAB will not activate any ABS components as
long as sensor inputs indicate normal braking.
During normal braking, the master cylinder, power
booster and wheel brake units all function as they
would in a vehicle without ABS. The HCU compo-
nents are not activated.
BRAKES - ABS
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