Traction Control System

PURPOSE
The traction control system is designed to maintain traction and reduce wheel slip at the front drive wheels on slippery surfaces during acceleration. This system is designed to operate at all vehicle speeds and reduces wheel slip by the use of engine torque management and brake intervention. The Electronic Brake (and Traction) Control Module (EBCM/EBTCM) monitors both front and rear wheel speeds through the wheel speed sensors.

OPERATION
If at any time during acceleration the EBCM/EBTCM detects front wheel slip, 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 spark firing angle and engine fueling and report the modified torque value back to the EBCM/EBTCM. Simultaneous with engine torque management, the EBCM/EBTCM will energize BPMV isolation valves, turn ON the BPMV pump motor and apply brake pressure to the over-spinning wheel(s). 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 to apply pressure, and begins cycling the BPMV's inlet and outlet valves. The inlet and outlet valve cycling aid in obtaining maximum road surface traction in the same manner as the antilock braking mode.

DIFFERENCE BETWEEN MODES
The difference between traction control mode and antilock braking modes is that brake fluid pressure is increased to lessen wheel spin (traction control mode), rather than reduced to allow greater wheel spin (antilock braking mode). 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. These pressure relief valves allow excess brake fluid volume to be returned to the master cylinder reservoir. If at any time during traction control mode, the brakes are manually applied, the BPMV pressure switch along with the brake switch, signal the EBTCM to disable traction control and allow manual braking. Manual braking also overrides the traction control system through the use of the isolation valves acting as one way check valves. This allows manual brake fluid pressure to be applied to the brake hydraulic system.