Antilock Brakes / Traction Control Systems: Description and Operation

Anti-Lock Control

Standard ABS
Standard ABS consists of the following components:
^ ABS module
^ Hydraulic control unit (HCU) (LH side of the engine compartment, behind the degas bottle)
^ Front wheel speed sensor
^ Front wheel speed sensor ring (press fit onto the brake disc)

The ABS prevents wheel lock-up by monitoring the front wheel speed sensors and the transmission output shaft speed (OSS) sensor, actuating the valves in the HCU, which modulates the brake pressure to the brake calipers. By preventing the wheels from locking up, the driver is able to maintain steering control and stop in the shortest possible distance under most conditions. The traction control system is controlled by the PCM and utilizes the ABS module for wheel speed information only. Engine only traction control (EOTC) helps maintain vehicle control during acceleration by modulating engine torque when driving on slippery or loose surfaces.

ABS with roll stability control (RSC) and traction control
ABS with RSC and traction control consists of the following components:
^ ABS module
^ HCU (LH side of the engine compartment, behind the degas bottle)
^ Front wheel speed sensor
^ Front wheel speed sensor ring (press fit onto the brake disc)
^ Rear wheel speed sensor
^ Rear wheel speed sensor ring (press fit onto the brake disc)
^ Stability control sensor cluster (under the passenger seat)
^ Steering wheel rotation sensor (attached to the steering column)

The ABS prevents wheel lock-up by monitoring the wheel speed sensors and actuating the valves in the HCU which modulates the brake pressure to the brake calipers. By preventing the wheels from locking up, the driver is able to maintain steering control and stop in the shortest possible distance under most conditions. The traction control system utilizes the same components as the ABS to prevent wheel spin and help maintain vehicle control during acceleration. The RSC system utilizes the same components as the ABS and the traction control systems and also monitors the steering wheel rotation sensor and the stability control sensor cluster to assist in stabilizing the vehicle during abrupt maneuvers.