Anti-Lock Brakes

Principles of Operations

Anti-Lock Control
The anti-lock brake system (ABS) module receives wheel speed readings from each wheel speed sensor and processes this information to determine if an ABS event is necessary. The wheel speed sensor electrically senses each tooth of the wheel speed sensor indicators as it passes through the wheel speed sensor magnetic field.

The active wheel speed sensor generates a signal that is sent to the ABS module. The wheel speed sensor circuitry connects to the ABS module through 2 wires and a connector at each wheel speed sensor. When the ignition is turned to the RUN position, the ABS module carries out a self-test by sending a reference voltage to all of the wheel speed sensors through their circuitry to determine if they are functional.

The ABS 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 ABS module returns the solenoid valves to their normal position, and normal (base) braking resumes.

The HCU has additional internal solenoid valves incorporated to enable control modulation of the wheel brake pressures.

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, and at above 20 km/h (12 mph) the pump motor is turned ON for approximately 1/2 second. Also, during all phases of operation the ABS module, with the vehicle in motion, checks for correct operation of the wheel speed sensors. Any malfunction of the ABS will cause the ABS to shut off. Normal power assisted braking, however, remains.

Traction Control System - All Wheel Drive (AWD)
The ABS module communicates with the powertrain control module (PCM) to assist with traction control. When the drive wheels lose traction and begin to spin, with vehicle speed under 100 km/h (62 mph), the ABS module requests the PCM to reduce engine torque while simultaneously appling and releasing the appropriate brake caliper(s) to maintain traction. The PCM accomplishes this by minor incremental timing changes and fewer fuel injector pulses until the ABS module ends the request. The request ends when the driven wheel speed returns to the desired speed. After the vehicle exceeds 100 km/h (62 mph), the traction control is accomplished only through the PCM torque control. The traction control system can be disabled by pressing the traction control switch and is indicated by the traction control light in the instrument cluster. The traction control system will reset and return to normal operation when the ignition switch is cycled, or when the traction control switch is pressed and released a second time during the same ignition cycle.

Traction Control System - Front Wheel Drive (FWD)
The traction control system is designed to limit wheel spin by modulating engine torque, in order to achieve maximum traction, when driving on slippery or loose surfaces. The traction control system can be disabled by pressing the traction control switch and is indicated by the traction control light in the instrument cluster. The traction control system will reset and return to normal operation when the ignition switch is cycled, or when the traction control switch is pressed and released a second time during the same ignition cycle.

ABS Module Configuration
ABS module configuration is not required on this vehicle.

Traction Control System Configuration - Front Wheel Drive (FWD)
The traction control system, for front wheel drive (FWD) vehicles, is contained in the PCM and is configured when the PCM is configured. Refer to Information Bus.

Traction Control System Configuration - All Wheel Drive (AWD)
Traction control system configuration is not required on AWD vehicles.