Traction Control System (TCS)

The traction control system is designed in order to maintain traction and reduce wheel slip at the front drive wheels on slippery surfaces during acceleration.

The system is designed to operate at all vehicle temperatures. The traction control system reduces wheel slip by the use of engine torque management and brake intervention.

The Electronic Brake (and Traction) Control Module (EBCM/EBTCM) monitors the front and the rear wheel speeds through the wheel speed sensors.

If the EBCM/EBTCM detects front wheel slip at any time during acceleration, it will request the PCM to bring excess engine torque into a specific range. This is accomplished via two high speed Pulse Width Modulated (PWM) circuits between the EBCM/EBTCM and the PCM.

The PCM will then adjust the spark firing angle and the engine fueling. The PCM will report the modified torque value back to the EBCM/EBTCM.

At the same time, the EBCM/EBTCM will complete the following actions:
^ Energize the BPMV isolation valves
^ Turn ON the BPMV pump motor
^ Apply brake pressure to the over-spinning wheels

The isolation valves isolate the front brake hydraulic circuits from the master cylinder and the rear brake hydraulic circuits. Once the front brake hydraulic circuits are isolated, pressure can be applied to the front wheels without affecting any other brake hydraulic circuit. The EBCM/EBTCM turns ON the BPMV pump motor in order to apply pressure. The EBCM/EBTCM begins cycling the BPMV's inlet and outlet valves.

The inlet and the outlet valve cyclings aid in obtaining the maximum road surface traction in the same manner as the antilock braking mode. The difference between traction control mode and antilock braking is indicated in the following list:
^ Traction Control Mode-The brake fluid pressure is increased in order to lessen wheel spin.
^ Antilock Braking Mode-The brake fluid pressure is reduced in order to allow greater wheel spin.

There are two pressure relief valves in the BPMV. This is because the BPMV pump motor supplies more brake fluid volume than required during traction control modes. The pressure relief valves allow excess brake fluid volume to be returned to the master cylinder reservoir.

If the brakes are manually applied at any time during the traction control mode, the BPMV pressure switch and the brake switch signal the EBTCM. The EBTCM disables traction control and allows manual braking.

Manual braking also overrides the traction control system through the use of the isolation valves. The isolation valves act as one way check valves. This allow manual brake fluid pressure to be applied to the brake hydraulic system.