Anti-Lock Brake System (ABS) Description

ANTI-LOCK BRAKE SYSTEM (ABS) DESCRIPTION
Anti-Lock Brake System Outline
^ During vehicle operation, including normal and antilock braking, the ABS control module monitors all electrical anti-lock functions and some hydraulic operations.
^ When the brakes are applied, brake fluid is sent through four normally open solenoid valves contained inside the ABS hydraulic control unit to each wheel.
^ If the control module senses a wheel is about to lock, it will prevent any more fluid from entering that wheel circuit.
^ Once the affected wheel comes back up to speed, the control module returns the valves to their normal condition allowing fluid to flow to the affected brake.
^ When the ignition is turned to RUN, the yellow ABS warning indicator will appear for three seconds as part of a system self-check.
^ A malfunction in the system will cause the control module to shut off or inhibit the system. However, normal power-assisted braking remains. Malfunctions are indicated by a yellow ABS warning indicator in the instrument cluster.





ABS Component Description

ABS Control Module
^ The ABS control module is mounted to the ABS hydraulic control unit.
^ The control module monitors system operation during normal driving and anti-lock braking.
^ Most faults that occur in the anti-lock brake system will be stored as a DTC.
^ During normal braking, the brake pedal feel will be identical to a conventional brake system.

Front and Rear Axle Speed Sensors
^ The anti-lock brake system uses three (two front and one rear) variable-reluctance speed sensors to determine vehicle speed.
^ As the teeth on the speed sensor indicator rotate past the sensor(s), a signal proportional to the speed of the rotation is generated and sent to the control module.

ABS Hydraulic Control Unit
^ The ABS hydraulic control unit consists of:
^ Brake pressure control valve block
^ Pump motor
^ The valve block and pump motor are replaced as an assembly.

G-Switch
^ The G-switch is used on 4x4 vehicles only.
^ The G-switch detects and indicates to the ABS control module that the vehicle is moving.
^ Without the G-switch, the control module would have no data to compare and would react as if the vehicle were stopped when in fact it is moving.