Brake System, Anti-Lock
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 Mark VIII is equipped with 4-wheel anti-lock brake system (ABS) with traction control as standard equipment.
The anti-lock brake system:
~prevents wheel lock-up by automatically modulating brake pressure during an emergency stop by not locking the wheels.
~allows driver to maintain steering control and stop vehicle in shortest possible distance under most conditions.
The anti-lock brake system consists of the following components:
~power brake booster (2005) and brake master cylinder (2140) assembly
~anti-lock brake hydraulic control unit
~anti-lock brake module (2C219)
~front brake anti-lock sensor (2C204)/rear brake anti-lock sensor (2C190)
~anti-lock brake pedal sensor switch (2C309)
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 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 (2C266), 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 module senses that 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 module then looks at the brake anti-lock sensor signal from the affected wheels again.
~If that wheel is still decelerating, it opens the normally closed solenoid valve for that circuit. This dumps any pressure that is trapped between the normally open valve and the brake back to the hydraulic control unit reservoir (2C246).
~Once the affected wheel comes back up to speed, the anti-lock brake module returns the valves to their normal condition allowing fluid flow to the affected brake.
~The anti-lock brake module monitors the electromechanical components of the system.
~Malfunction of the anti-lock brake system will cause the anti-lock brake module to shut off or inhibit the system. However, normal power-assisted braking remains.
~Malfunctions are indicated by one of two warning indicators inside the vehicle.
~Loss of hydraulic fluid in the hydraulic control unit reservoir will disable the anti-lock system.
~The 4-wheel anti-lock brake system is self-monitoring. When the ignition switch is turned to the RUN position, the anti-lock brake module will perform a preliminary self-check on the anti-lock electrical system indicated by a three-to-four second illumination of the amber CHECK ANTI-LOCK BRAKE indicator in the instrument cluster (10849).
~During vehicle operation, including normal and anti-lock braking, the anti-lock brake module monitors all electrical anti-lock functions and some hydraulic operations.
~Each time the vehicle is driven, as soon as vehicle speed reaches approximately 30 km/h (19 mph), the anti-lock brake module turns on the pump motor (2C256) 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 module.
~In most malfunctions of the anti-lock brake/traction control system, the amber CHECK ANTI-LOCK BRAKE and/or red BRAKE indicator(s) will be illuminated.
~The sequence of illumination for these indicators combined with the actual symptoms can determine the appropriate diagnostic tests to perform. Most malfunctions are recorded as a diagnostic trouble code (DTC) in the anti-lock brake module and assist in pinpointing the component needing service.