Traction Control System

DESCRIPTION
Traction control is offered as an option on vehicles equipped with ABS. Traction control is designed to control wheel spin when accelerating on slippery surfaces. Many of the components used in traction control operation are shared with the ABS. Use the ABS information for diagnosis and repair.

OPERATION
During acceleration, if one or both rear wheels lose traction and begin to spin, the traction control system will rapidly apply and release the appropriate rear brake to reduce wheel spin and add traction. The traction control system monitors brake usage to prevent brake overheating. If the traction control system is turned off by the ABS control module to prevent the rear brakes from overheating, the indicator lamp in the traction control switch will be illuminated. This will not affect the ABS operation. The traction control system operates at vehicle speeds up to approximately 55 km/h (34 mph).

ANTI-LOCK CONTROL AND MODULE ASSEMBLY
The traction control system is controlled by the ABS control module. The ABS control module is located on the ABS hydraulic control bracket. It is an on-board diagnostic, non-serviceable unit consisting of two microprocessors and the necessary circuitry for their operation. These microprocessors are programmed identically. The ABS control module monitors system operation during normal driving as well as during ABS braking and traction control cycling. Most faults which occur to the ABS and the traction control will be stored as a diagnostic trouble code (DTC) in the keep-alive memory of the ABS control module. The DTCs can be retrieved by following the ABS on board diagnostic procedures. Testing and Inspection

HYDRAULIC CONTROL UNIT
Description
The ABS hydraulic control unit is located outside of the engine compartment on a bracket which attaches to the outer frame rail. It consists of the following components:
- Brake pressure control valve block assembly
- Pump motor
- Hydraulic control unit reservoir with fluid level indicator assembly
- Anti-lock brake control module
- Anti-lock brake tube
- Anti-lock brake hydraulic control bracket

Operation
Operation of hydraulic control unit for traction control is as follows: The traction control valve body contains two isolation valves for traction control function; one for the primary circuit and one for the secondary circuit. The isolation valves close during traction control operation to prevent front brake operation.

Servicing
Other than seals, gaskets and screws no internal parts can be serviced. Refer to ABS Service and Repair. The following components are serviced separately:
- Brake pressure control valve block.
- Pump motor.
- Hydraulic control unit reservoir.
- Anti-lock brake control module.
- Anti-rock brake tube.
- Anti-lock brake hydraulic control bracket.

TRACTION CONTROL SWITCH
The traction control switch is located on the center instrument panel left of the fluid level indicator lights. When activated, the traction control switch sends a signal to the ABS control module which prevents traction control operation. An amber light on the traction control switch will illuminate showing the traction control system is disengaged. Activating the traction control switch again or cycling the ignition switch from "OFF" to "RUN" will enable the system.

BRAKE SENSOR, ANTI-LOCK
The traction control system uses the existing ABS sensors. The ABS uses four sets of variable-reluctance sensors to determine the rotational speed of each wheel. The sensors operate on magnetic induction principle. As the teeth on the tone ring rotate past the sensor, a signal proportional to the speed of the rotation is generated and sent to the ABS control module through a twisted pair wire harness. The front brake ABS sensors and rear brake ABS sensors are not adjustable.