Traction Control: Notes

Traction control utilizes ABS components to detect and control excessive rear wheel spin on low-traction surfaces.

When the drive wheels lose traction on a low-traction surface, with vehicle speed under 100 km/h (62 mph), the ABS module commands the hydraulic pump motor on and commands the HCU to open and close the appropriate solenoid valves to modulate the brake pressure to the rear brake caliper(s) while simultaneously sending a request to the PCM over the High Speed Controller Area Network (HS-CAN) bus to reduce engine torque to maintain vehicle traction. The PCM accomplishes this by minor incremental timing changes and fewer fuel injector pulses until the ABS module ends the request. The request ends when the driven wheel speed returns to the desired speed. After the vehicle speed exceeds 100 km/h (62 mph), the traction control is accomplished only through the PCM torque control. During a traction control event, the traction control indicator in the instrument cluster will flash.

The intention of traction control is to detect and control excessive rear wheel spin on low-traction surfaces. On high-traction surfaces, a controlled amount of rear wheel spin will be allowed in the interest of quick acceleration. In order to avoid unnecessary traction control activation, the traction control strategy uses several inputs to determine when traction control activation is beneficial to the driver. The PCM relays throttle position information to the ABS module over the HS-CAN bus. The throttle position is utilized to determine if the driver intends to accelerate quickly. If this is the case, traction control will allow a controlled amount of rear wheel spin. If rear wheel spin is permitted, input from the front wheel speed sensors will be used to calculate vehicle acceleration. If the vehicle is accelerating while wheel spin is occurring, the ABS module will check for a difference between the left front and right front wheel speeds to determine if the vehicle is accelerating in a straight line. If the vehicle is not accelerating (rear wheels spinning on a slippery surface) or if the vehicle is turning, traction control will activate to help make better use of the available traction.