Antilock Brakes / Traction Control Systems: Description and Operation
Anti-Lock Control
ABS With Traction Control and Electronic Stability Control (ESC)
The ABS with traction control and Electronic Stability Control (ESC) consists of the following components:
- ABS module - attached to the Hydraulic Control Unit (HCU), but can be serviced separately.
- Front wheel speed sensors - one sensor is located in each front wheel knuckle. The sensors are serviced separately from the knuckle.
- Front wheel speed sensor tone rings - one tone ring is located in each wheel bearing and wheel hub assembly and is serviced with the wheel bearing and wheel hub.
- HCU - which contains several valves (inlet, outlet, isolation and dump), the hydraulic pump motor and is mounted behind the battery and battery tray.
- Rear wheel speed sensors - one sensor is located in each rear wheel knuckle, the sensors are serviced separately from the knuckle.
- Rear wheel speed sensor tone rings - one tone ring is located in each wheel bearing and wheel hub assembly and is serviced with the wheel bearing and wheel hub.
- Stability control sensor cluster - located under the rear of the front floor console and contains several sensors (yaw rate, lateral accelerometer and longitudinal accelerometer).
- Steering wheel rotation sensor - located on the RH side of the clock spring and is serviced separately from the clock spring assembly.
- Stability/traction control switch - located in the instrument panel finish panel and is serviced separately from the finish panel.
Electronic Brake Distribution (EBD)
The ABS module and HCU incorporate a strategy called Electronic Brake Distribution (EBD). The EBD strategy uses the HCU as an electronic proportioning valve to create a balanced braking condition between the front and rear wheels and minimize the chance of rear wheel lockup during hard braking.
Anti-Lock Control
The anti-lock control system aids in the prevention of wheel lock-up during braking events which will allow the driver to maintain steering control and stop in the shortest distance possible under most conditions. This is accomplished by the ABS module and HCU modulating brake fluid pressure to the affected brake caliper(s).
- A rumble or grinding sound may be heard
- If the driver's foot is on the brake pedal, a vibration may be felt in the brake pedal
Traction Control System
The traction control system aids in the prevention of excessive wheel spin which will allow the vehicle to maintain traction during acceleration. This is accomplished by the ABS module and the HCU modulating brake fluid pressure to the affected brake caliper(s) and by the PCM modulating engine torque.
When the traction control system activates, any of the following can occur:
- A rumble or grinding sound may be heard much like ABS
- A small deceleration or a reduction in the acceleration of the vehicle
- The stability/traction control indicator ("sliding car" icon) flashes
- If the driver's foot is on the brake pedal, a vibration may be felt in the brake pedal much like ABS
Electronic Stability Control (ESC) System
The ESC system constantly monitors the direction of travel relative to the driver's intended course, except when the vehicle is traveling in reverse, and aids in keeping the vehicle traveling along that course. This is accomplished by the ABS module and the HCU modulating brake fluid pressure to the affected brake caliper(s) and by the PCM modulating engine torque.
When the ESC system activates, any of the following can occur:
- A rumble or grinding sound may be heard much like ABS
- A small deceleration or a reduction in the acceleration of the vehicle
- The stability/traction control indicator ("sliding car" icon) flashes
- If the driver's foot is on the brake pedal, a vibration may be felt in the brake pedal much like ABS
Stability/Traction Control Switch
The stability/traction control switch can be used by the driver to disable and enable the traction control system. When the switch is pressed, the traction control system is disabled. When the system is disabled, the stability/traction control indicator ("sliding-car icon") in the Instrument Cluster (IC) (or message center if equipped) will illuminate. The standard anti-lock control system and ESC system cannot be disabled through the use of the stability/traction control switch.