Principles of Operation

Principles of Operation
The anti-lock brake system (ABS) module receives wheel speed readings from both front wheel speed sensors and the differential speed sensor. The ABS module then processes this information, along with other sensor inputs, to determine if an ABS event is necessary. The wheel speed sensor electrically senses each tooth on the ABS sensor indicators as it passes through the wheel speed sensor's magnetic field.

The ABS module continuously monitors and compares the rotational speed of each front wheel and the speed of the rear differential. When impending wheel lockup is detected the ABS module will modulate brake pressure to the appropriate brake caliper(s) and rear brakes. 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 ABS module returns the solenoid valves to their normal position, and normal (base) braking resumes.

The ABS module is self-monitoring. When the ignition switch is turned to the RUN position, the ABS module will do a preliminary electrical check. At approximately 20 km/h (12 mph), the pump motor is turned on for approximately 1/2 second. Any malfunction of the ABS will cause the ABS to deactivated and the ABS warning indicator to illuminate; however, normal power-assisted braking remains.

Dynamic Rear Proportioning (DRP)
Vehicles with 4 wheel disc brakes are equipped with dynamic rear proportioning (DRP). The DRP system is integral to the ABS module. The DRP maintains brake balance and maximizes brake efficiency for all loading configurations. DRP detects the onset of front versus rear slip imbalance and limits the rear pressure. If the rear slip significantly exceeds the front slip, the DRP system will reduce the rear pressure. If this condition occurs, the driver will feel a slight pulsation in the brake pedal. The DRP system will be disabled if diagnostic trouble code (DTC) C1226 is set or if a DTC is set from condition 1 and condition 2 or condition 3, or if 1 DTC from condition 2 and condition 3, or if 2 or more DTCs are set from condition 1.

Condition 1:
^ C1095
^ C1196
^ C1200
^ C1212
^ C1216

Condition 2:
^ C1155
^ C1158
^ C1233

Condition 3:
^ C1145
^ C1148
^ C1234

If any DTCs are retrieved, GO to Inspection and Verification. Inspection and Verification