Operation

WARNING: Brake fluid contains polyglycol 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 vehicle is equipped with a 4-wheel Anti-Lock Brake System (ABS) with optional Traction Control (TC).

The anti-lock brake system:
- Prevents wheel lock-up by automatically modulating brake pressure during an emergency stop.
- Allows the driver to maintain steering control and stop the vehicle in the shortest possible distance under most conditions.

The Anti-Lock Brake System (ABS) operates as follows:
- When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the Hydraulic Control Unit (HCU) inlet ports. This pressure is transmitted through four normally open solenoid valves contained inside the HCU, then through the outlet ports of the HCU to each wheel.
- The primary (rear) circuit of the brake master cylinder feeds the front brakes.
- The secondary (front) circuit of the brake master cylinder feeds the rear brakes.
- If the anti-lock brake control module senses a wheel is about to lock, based on anti-lock brake 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 anti-lock brake sensor signal from the affected wheel again.
- If that wheel is still decelerating, it opens the solenoid valve for that circuit to reduce hydraulic pressure.
- Once the affected wheel comes back up to speed, the anti-lock brake control module returns the solenoid valves to their normal condition allowing fluid flow to the affected brake.
- The anti-lock brake control module monitors the electromechanical components of the system.
- 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.
- Malfunctions are indicated by the yellow ABS warning indicator on the instrument cluster.
- The 4-wheel anti-lock brake system 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 on 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.
- Most malfunctions of the anti-lock brake system and traction control system, if equipped, will cause the yellow ABS warning indicator to illuminate.

Operation of the hydraulic control unit is as follows:
- During normal braking, fluid passes through four normally open inlet valves, one to each wheel.
- If the anti-lock brake control module senses a wheel is about to lock, it pulses the appropriate inlet valve which closes that valve. This prevents any more fluid from entering the affected brake.
- The anti-lock brake control module then looks at that wheel again. If it is still decelerating, it opens the normally closed outlet valve which decreases the pressure trapped in the line.
- The traction control portion of the brake pressure control valve block 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 application.

Anti-lock brake control module operation is as follows:
- Under normal driving conditions, the microprocessor produces short test pulses to the solenoid valves that check the electrical system without any mechanical reaction.
- Impending wheel lock conditions trigger signals from the anti-lock brake control module that open and close the appropriate solenoid valves. This results in moderate pulsations in the brake pedal.
- During normal braking, the brake pedal feel will be identical to a standard brake system.
- Most faults which occur to the anti-lock brake system and the traction control will be stored as a Diagnostic Trouble Code (DTC) in the keep-alive memory of the anti-lock brake control module. The DTCs can be retrieved by following the on-board diagnostic procedures.

The anti-lock brake system uses one yellow ABS warning indicator to alert the driver of malfunctions in the system.

The yellow ABS warning indicator will illuminate 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 system. Normal power assisted braking remains but the wheels can lock during a panic stop while the yellow ABS warning indicator is illuminated.

The anti-lock brake system uses four variable-reluctance sensors to determine vehicle speed. The anti-lock brake sensors operate on magnetic induction principles. As the teeth on the anti-lock brake sensor indicator rotate past the stationary anti-lock brake sensor, a signal proportional to vehicle speed is generated and sent to the anti-lock brake control module.