Principles Of Operation

WARNING: Brake fluid contains polyglyco ethers and polyglycols. Avoid contact with eyes. Wash hands thoroughly after handling. If brake fluid contacts eyes, flush eyes with running water for 15 minutes. Get medical attention if irritation persists. If taken internally, drink water and induce vomiting. Get medical attention immediately.

The ABS operates as follows:

When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the brake pressure control valve block inlet ports. This pressure is transmitted through four normally open solenoid valves contained inside the brake pressure control valve block and then through the outlet ports of the brake pressure control valve block to each wheel.
The primary (rear) circuit of the brake master cylinder feeds the right front and left rear brakes.
The secondary (front) circuit of the brake master cylinder feeds the left front and right rear brakes.
If the anti-lock brake control module senses a wheel is about to lock, based on brake anti-lock sensor data, it closes the normally open solenoid valve for that circuit. This prevents any more fluid from entering that circuit.
The anti-lock brake control module then looks at the brake anti-lock sensor signal from the affected wheels again.
If that wheel is still decelerating, it opens the closed solenoid valve for that circuit.
Once the affected wheel comes back up to speed, the anti-lock brake control module returns the valves to their normal condition, allowing fluid to flow to the affected brake.
Any malfunction of the anti-lock brake system will cause the anti-lock brake control module to shut off or inhibit the system. However, normal power-assisted braking remains.
The 4-wheel ABS is self-monitoring. When the ignition switch is turned to the RUN position, the anti-lock brake control module will perform a preliminary self-check of the anti-lock electrical system indicated by a three-second illumination of the yellow ABS warning indicator in the instrument cluster.
During vehicle operation, including normal and anti-lock braking, the anti-lock brake control module monitors all electrical anti-lock functions and some hydraulic operations.
Each time the vehicle is driven, as soon as vehicle speed reaches approximately 20 km/h (12 mph), the anti-lock brake control module turns on the pump motor for approximately one-half second. At this time, a mechanical noise may be heard. This is a normal function of the self-check by the anti-lock brake control module.
For most malfunctions of the anti-lock brake with traction control system, the yellow ABS warning indicator will be illuminated.

The traction control system is operational when the ignition switch is in the RUN position.

It can be disabled by the driver by entering the traction control OFF setting in the vehicle message center. The traction control system will reset and return to the traction control ON setting when the ignition switch is cycled.

The traction control system applies and releases the appropriate front brake to reduce wheelspin and to aid traction if one or both front wheels lose traction and begin to spin during acceleration. TRACTION CONTROL ACTIVE is displayed on the message center during system operation.

The system interacts with the powertrain control module to reduce engine torque if one or both front wheels lose traction and begin to spin during acceleration.

If the traction control system is in operation continually on slippery roads, the anti-lock brake control module may disable the system to prevent overheating of the front brakes.

When the cool down time limit expires, traction control is restored. (Anti-lock braking is fully functional during the cool down period.)

The ABS uses the yellow ABS warning indicator to alert the driver of malfunctions in the system.

The yellow ABS warning indicator will come on for numerous reasons. It warns the driver that the ABS and traction control have been turned off due to a symptom that exists in the ABS system. Normal power-assisted braking remains but the wheels can lock during a panic stop while the yellow ABS warning indicator is on.

In addition to the yellow ABS warning indicator described above, the traction control system uses the message center to alert the driver of faults unique to the traction control system. CHECK TRACTION CONTROL is displayed on the message center to alert the driver that traction control is disabled due to a symptom in the traction control system.

The anti-lock brake control module monitors system operation and can store all defined DTCs in its memory. The anti-lock brake control module CANNOT recognize some failures. Therefore, if a symptom exists and no DTCs are stored by the anti-lock brake control module, other diagnostic steps must be followed.

The anti-lock brake control module cannot store a DTC if there is no power to the anti-lock brake control module. This condition can be found by using the Anti-Lock Quick Check Sheet.

After the failures have been repaired and you have confirmed the vehicle functions properly, use scan tool to clear all DTCs from the anti-lock brake control module.

After clearing the DTCs, the ignition switch must be cycled from RUN to OFF to RUN.

The anti-lock brake control module will automatically clear DTCs that have not recurred after 80 ignition cycles, provided the vehicle has reached 24 km/h (15 mph) between each ignition cycle. (Simply turning the ignition switch from OFF to RUN 80 times will not clear the DTCs.)