Principles of Operation

Principles of Operation
The traction control module executes control of the Anti-Lock Brakes (ABS) and full speed traction control functions to enhance driver control of the vehicle. The traction control module manages the interactions between the anti-lock, traction control, and engine control systems to optimize the vehicle traction during deceleration and acceleration.

The traction control module is operational with the ignition switch in the RUN or START positions and is part of the Hydraulic Control Unit (HCU). The traction control module and HCU are replaced as an assembly.

The traction control module continuously monitors and compares the rotational speed of each wheel. The rotational speed is measured by the ABS sensor which electrically senses each tooth of the wheel speed sensor ring as they pass through the sensor's magnetic field.

The traction control module is self-monitoring. When the ignition switch is turned to the RUN position, the traction control module will carry out a preliminary electrical check. At approximately 20 km/h (12 mph) the pump motor is turned on for approximately 0.5 second. Any concern with the traction control system will cause the traction control system to shut off, the ABS warning indicator to illuminate and the power assist braking system to function normally.

The traction control module communicates with the powertrain control module (PCM) requesting assistance with traction control. At speeds under 40 km/h (25 mph) the traction control module requests the PCM to reduce engine torque, while simultaneously applying and releasing the appropriate brake to restore traction when one or both drive wheels lose traction and begin to spin. The PCM accomplishes this by minor incremental ignition timing changes and fewer fuel injector pulses until the driven wheel speed returns to normal and the traction control module ends the request. After the vehicle speed exceeds 40 km/h (25 mph), the traction control is accomplished only by the PCM controlling the torque.

The traction control system helps maintain vehicle traction at the limits of tire adhesion. System effectiveness varies with vehicle speed, road conditions, and steering inputs.

The traction control system defaults to ON when the engine is started. In reverse, ABS and traction control are inoperative. The traction control switch allows the driver to control the ON/OFF operation of the traction control system (independent of the ABS function). The ABS system cannot be switched off by the driver. The traction control system status is indicated by a traction control system warning light. An illuminated traction control warning light indicates the system is switched off.

During a traction control event you may experience any of the following normal behaviors:
^ a rumble or grinding sound much like ABS
^ a small deceleration of the vehicle
^ the traction control indicator will flash

The traction control system continually monitors all sensors and actuators used to improve the traction control of the vehicle. Some drivers may notice a slight movement of the brake pedal when the system checks itself If the brake system has not been bled correctly, the brake pedal movement may become more significant. The ABS function will continue to work as designed unless the yellow ABS warning indicator is also illuminated. The normal brake function should always occur, unless the red brake warning indicator is illuminated.

Brake Booster The brake booster is a normal power-assisted brake booster.

The master cylinder attached to the booster functions normally.