Antilock Brakes / Traction Control Systems: Description and Operation
Anti-Lock Control
ABS With Traction Control and AdvanceTrac(R)
The ABS with traction control and AdvanceTrac(R) 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 of the front wheel bearing inner seals and is serviced with the wheel bearing.
- HCU (Hydraulic Control Unit)- which contains several valves (inlet, outlet, isolation and dump), the hydraulic pump motor and is mounted behind the battery and battery tray. The HCU (Hydraulic Control Unit) is available only with a new ABS module.
- 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 of the rear wheel bearing inner seals and is serviced with the wheel.
- Steering Angle Sensor Module (SASM)- vehicles that are equipped with Electronic Power Assist Steering (EPAS), but without the Active Park Assist feature have a SASM (Steering Angle Sensor Module) which does not have any electrical components inside. It is only installed to provide structural support for the clockspring and for turn signal canceling. On these vehicles, the steering wheel rotation and angle information is sent from the Power Steering Control Module (PSCM). Vehicles with the Active Park Assist feature have a fully functional SASM (Steering Angle Sensor Module) and receive steering wheel information from the SASM (Steering Angle Sensor Module).
- Steering wheel rotation sensor, vehicles with Hydraulic Power Assist Steering (HPAS) only- located on the RH side of the clockspring and is serviced separately from the clockspring assembly.
- Steering wheel rotation sensor ring, vehicles with HPAS (Hydraulic Power Assist Steering) only- located on the clockspring and is serviced with the clockspring assembly.
- Stability/traction control switch- depending on vehicle options, the switch is located in the Front Controls Interface Module (FCIM) (and is serviced with the module) or the HVAC module (and is serviced with the module).
Electronic Brake Distribution (EBD)
The ABS module and HCU (Hydraulic Control Unit) incorporate a strategy called Electronic Brake Distribution (EBD). The EBD (Electronic Brake Distribution) strategy uses the HCU (Hydraulic Control Unit) 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. A slight bump may be felt in the brake pedal when the EBD (Electronic Brake Distribution) is active.
ABS with Advance Trac
The AdvanceTrac(R) system is made up of the following 2 distinct vehicle systems:
- Traction Control System- helps to avoid excessive drive-wheel spin and loss of traction.
- Electronic Stability Control (ESC)- helps to avoid skids and lateral slides.
Traction Control System
The traction control system aids in the prevention of excessive wheel spin which allows the vehicle to maintain traction during acceleration. This is accomplished in the same manner as anti-lock braking but also includes the use of the PCM for modulating engine torque.
ESC (Electronic Stability Control)
The ESC (Electronic Stability Control) system constantly monitors vehicle direction of travel relative to the driver's intended course and aids in keeping the vehicle traveling along that course. This is accomplished in the same manner as anti-lock braking and traction control.
When one or both of the above systems activate, the driver may notice the same operational symptoms as ABS along with the following additional symptoms:
- A small deceleration or a reduction in the acceleration of the vehicle (PCM modulating engine torque)
- The stability/traction control indicator (also known as the sliding-car icon) flashes (indicating a traction or stability event is taking place)
Stability/Traction Control Indicators
There are 2 separate sliding car icons; the sliding car OFF icon and the sliding car icon. The sliding car OFF icon is used to alert the driver that the traction control portion of the AdvanceTrac(R) system has been disabled. This icon only illuminates continuously and does not flash. The sliding car icon is used to alert the driver that a stability/traction event is taking place (flashes twice per second) and to alert the driver of potential concerns in the AdvanceTrac(R) system (illuminates solidly).
Traction Control Switch
The traction control switch provides the driver with the ability to turn the traction control system off. When the switch is pressed, the sliding-car OFF icon in the Instrument Panel Cluster (IPC) illuminates continuously, indicating that the traction control system is off. Pressing the switch once re-enables normal traction control operation. The conventional ABS cannot be disabled through the use of the traction control switch.