Traction Control and Traction Control with Advance Trac®/IVD: Notes

With the ignition in the START or RUN positions, the traction control module functions similarly to a conventional anti-lock brake module by monitoring and comparing the rotational speed of each wheel. Wheel speeds are measured by the wheel speed sensor which electrically senses each tooth of the anti-lock sensor ring as they pass through the sensor's magnetic field. When the traction control module detects an impending wheel lock, wheel spin or vehicle motion that is inconsistent with the driver's commands, brake pressure is modulated to the appropriate brake caliper(s). The traction control module triggers the hydraulic control unit (HCU) to open and close the appropriate solenoid valves. Once the affected wheel(s) return to the desired speed, the traction control module returns the solenoid valves to their normal position, and normal base brake operation is restored.

The traction control module communicates with the powertrain control module (PCM) to assist with traction control. At speeds under 40 km/h (25 mph), when drive wheels lose traction and begin to spin, the traction control module requests the PCM to reduce engine torque, while simultaneously applying and releasing the appropriate brake caliper(s) to maintain traction. The PCM accomplishes this by minor incremental timing changes and fewer fuel injector pulses until the traction control module ends the request. The request ends when the driven wheel speed returns to normal. After the vehicle speed exceeds 40 km/h (25 mph), the traction control is accomplished only through the PCM torque control.

The Advance Trac®/IVD system constantly monitors vehicle motion relative to the driver's intended course. This is done by using sensors to compare the driver's steering input and brake application with that of the actual vehicle motion. The system does not activate when the vehicle is traveling in reverse, however, ABS and traction control will continue to function as usual.

The Advance Trac®/traction control switch allows the driver to control use of the Advance Trac®/IVD system. This is independent of the ABS function, which cannot be switched off by the driver. The Advance Trac®/IVD system's status is indicated by a traction control warning light in the Advance Trac®/traction control switch. An illuminated Advance Trac®/traction control switch indicates that the Advance Trac®/IVD system is switched off. In the message center, the message "Advance Trac OFF/Traction Control OFF" is displayed. However, if another alert message is being displayed on the message center ("Door Ajar"), the "Advance Trac OFF/Traction Control OFF" message may not be displayed. If a failure is detected somewhere in the Advance Trac®/IVD system which affects either the yaw control or traction control functions, the traction control indicator will illuminate. The anti-lock brake function continues to work as designed unless the yellow anti-lock brake warning indicator is also illuminated. The normal brake function always occurs, unless the red brake warning indicator is illuminated.

When Advance Trac® activates, any of the following can occur:

• a rumble or grinding sound much like ABS with traction control
• a small deceleration or a reduction in the acceleration of the vehicle
• the traction control indicator will flash
• if the driver's foot is on the brake pedal, a vibration will be felt in the pedal much like ABS
• if the event is severe and the driver's foot is not on the brake, the solenoid in the active booster will be energized by the traction control module. In the case of a severe event, you may notice brake pedal movement, a "whoosh" sound and/or a loud vibration from the brake pedal.

Some drivers may notice a slight movement of the brake pedal when the Advance Trac®/IVD system checks itself. The brake pedal moves when an active test of the brake booster is run. During this test a small amount of pressure will be generated at the master cylinder, but no pressure will be generated in the brake calipers. This test will occur above 48 km/h (30 mph) after the vehicle has been running approximately 8 minutes. The test will only be run if the vehicle is stable, the driver is not braking and the accelerator pedal is slightly pressed. If the brake system is not bled correctly, the brake pedal movement can become more significant.