Traction Control System (TCS) Operation

DESCRIPTION - TRACTION CONTROL SYSTEM
Traction control reduces wheel slip and maintains traction at the driving wheels at speeds below 56 km/h (35 mph) when road surfaces are slippery. The traction control system reduces wheel slip by braking the wheel that is losing traction.
OPERATION - TRACTION CONTROL SYSTEM
The Controller Antilock Brake (CAB) monitors wheel speed. During acceleration, if the CAB detects front (drive) wheel slip and the brakes are not applied, the CAB enters Traction Control (TC) mode. TC operation proceeds in the following order:
1. Close the normally open TC valves.
2. Start the pump/motor and supply volume and pressure to the front (drive) hydraulic circuit. (The pump/motor runs continuously during traction control operation.)
3. Open and close the build and decay solenoid valves to maintain minimum wheel slip and maximum traction.
The cycling of the build and decay valves during traction control is similar to that during antilock braking, except the valves work to control wheel spin by applying the brakes, whereas the Antilock Brake System (ABS) function is to control wheel skid by releasing the brakes.
Two pressure relief shuttle valves allow pressure and volume to return to the master cylinder reservoir when not consumed by the build and decay valves. These valves are necessary because the pump/motor supplies more volume than the system requires.
If the brakes are applied at anytime during a TC cycle, the brake lamp switch triggers the control module to switch off TC.
The TC function indicator illuminates during a traction control cycle, displaying TRAC on the instrument panel.
The TC system is enabled at each ignition cycle. It may be turned off by depressing the TC switch button. The TC function indicator (TRAC OFF) illuminates immediately upon depressing the button. Pressing this button again or turning off and restarting the vehicle will enable the TC system.
If the CAB calculates that the brake temperatures are high, the TC system becomes inoperative until a time-out period has elapsed. During this "thermo-protection mode," the TC function indicator illuminates TRAC OFF; note that no trouble code is registered.