Principles of Operation

Special Tool(s)

Principles of Operation
The anti-lock brake control module receives wheel speed readings from both front wheel speed sensors and the rear differential speed sensor, and 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 anti-lock brake control module continuously monitors and compares the rotational speed of each wheel speed sensor indicator and, when it detects an impending wheel lock, modulates brake pressure to the appropriate brake caliper(s). 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 control module returns the solenoid valves to their normal position, and normal (base) braking resumes.
The ABS control module is self-monitoring. When the ignition switch is turned to the RUN position, the ABS 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 system will cause the ABS to shut off; however, normal power assisted braking remains.

Dynamic Rear Proportioning (DRP)
Vehicles with four wheel disc brakes are equipped with dynamic rear proportioning (DRP). The DRP system is integral to the anti-lock brake control 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 one diagnostic trouble code (DTC) is set from condition 1 and condition 2 or condition 3, or if one DTC from condition 2 and condition 3, or if two or more DTC'S are set from condition 1.
Condition one:
^ C1095
^ C1196
^ C1200
^ C1212
^ C1216
Condition two:
^ C1155
^ C1158
^ C1233
Condition three:
^ C1145
^ C1148
^ C 1234
If any DTC'S are retrieved, GO to Inspection and Verification - NGS. Initial Inspection and Diagnostic Overview