Traction Control

The Traction Control System (TCS) is designed to maintain traction and reduce wheel over spin at the front drive wheels on slippery surfaces during acceleration. The system, designed to operate at all vehicle speeds, reduces wheel slip by braking the wheel that is loosing traction.

The Electronic Brake And Traction Control Module (EBTCM) monitors both front and rear wheel speeds through the wheel speed sensors. If at any time during acceleration the EBTCM detects front wheel slip, it will request the Powertrain Control Module (PCM) to bring excess engine torque into a specific range. This is accomplished via two high speed Pulse Width Modulated (PWM) circuits between the EBTCM and the PCM. The PCM will then adjust spark firing angle and engine fueling and report the modified torque value back to the EBTCM. Simultaneous with engine torque management, the EBTCM will energize PMV isolation valves, turn on the PMV 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 EBTCM turns on the PMV pump motor to apply pressure, and begins cycling the PMV assembly'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. The difference between traction control mode and antilock braking mode 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 PMV assembly. This is because the PMV 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 PMV pressure switch and the brake switch signal the EBTCM to disable traction control and allow manual braking. Manual braking also overrides the traction control system through use of the isolation valves which act as one way check valves. This allows manual brake fluid pressure to be applied to the brake hydraulic system.