Four Wheel Antilock Brake System (4WABS)

DESCRIPTION AND OPERATION
Anti-Lock Control The 4-wheel, 4-channel Anti-Lock Brake System (4WABS) consists of the following components:
^ Anti-lock brake control module
^ Front wheel speed sensor
^ Front wheel speed sensor ring
^ Hydraulic control unit
^ Rear wheel speed sensor
^ Rear wheel speed sensor ring
^ Yellow ABS warning indicator

Principles of Operation
The anti-lock-brake control module receives wheel speed readings from each anti-lock brake sensor and processes this information to determine if an ABS event is necessary. The anti-lock brake sensor electrically senses each tooth of the anti-lock brake sensor indicators as it passes through the anti-lock brake sensor magnetic field.
The anti-lock brake control module continuously monitors and compares the rotational speed of each wheel and, when it detects an impending wheel lock, modulates brake pressure to the appropriate brake caliper. This is accomplished by triggering the Hydraulic Control Unit (HCU) to open and close the appropriate solenoid valves. Once the affected wheel returns to normal speed, the anti-lock brake control module returns the solenoid valves to their normal position, and normal (base) braking resumes.
The anti-lock brake control module is self-monitoring. When the ignition switch is turned to the RUN position, the anti-lock brake control module will do a preliminary electrical check, and at approximately 20 km/h (12 mph) the pump motor is turned on for approximately one-half second. Any malfunction of the ABS will cause the ABS or Anti-Lock Brake System (ABS) to shut off and the yellow anti-lock brake warning indicator to illuminate. However, the power assist braking system functions normally.

Electronic Brake Distribution
The Electronic Brake Distribution (EBD) controls rear brake pressure and acts as an electronic proportioning valve. It is controlled by the anti-lock brake control module. When EBD is disabled, the amber ABS warning indicator and the red brake warning indicator will illuminate.