Antilock Brakes / Traction Control Systems: Description and 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.
Taurus and Sable vehicles have a 4-wheel anti-lock brake system as an option.
The system operates as follows:
- Prevents wheel lockup during an emergency stop by modulating brake pressure.
- Permits the driver to maintain steering control and stop the vehicle in the shortest possible distance under most conditions.
- During the anti-lock brake operation, the driver will sense a pulsation in the brake pedal and a clicking sound.
- The pedal effort and pedal feel during normal braking are similar to that of a conventional power brake system.
The anti-lock brake system consists of the following major components:
- front brake anti-lock sensor/rear brake anti-lock sensor.
- anti-lock brake control module.
- anti-lock brake hydraulic control unit.
Anti-Lock Brake System (ABS) operates as follows:
- If the anti-lock brake control module senses that a wheel is about to lock, based on brake anti-lock sensor data, it pulses the normally open solenoid valve closed 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 wheel again.
- If that wheel is still decelerating faster than the other three wheels, 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 brake master cylinder reservoir.
- Once the affected wheel returns to speed, the anti-lock brake control module returns the valves to their normal condition allowing fluid flow to the affected brake.
- The anti-lock brake control module monitors the electro-mechanical 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 a warning indicator in the instrument cluster.
- The 4-wheel anti-lock brake system is self monitoring. When the ignition switch is placed in the RUN position, the anti-lock brake control module will perform a preliminary self check on the anti-lock electrical system indicated by a two second illumination of the amber ABS 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.
- In most malfunctions of the anti-lock brake system, the amber ABS indicator will be illuminated.
- Most malfunctions are recorded as a Diagnostic Trouble Code (DTC) in the anti-lock brake control module keep-alive random access memory and assist in pinpointing the component needing service.
Electrical System
Power is provided to the anti-lock brake control module through three separate fused lines for electronic logic control, hydraulic pump motor and solenoid valves. Four brake anti-lock sensors provide a pulsing (square wave) signal that varies with wheel speed. Signal inputs to the anti-lock brake control module are:
- battery positive voltage (B+).
- front brake anti-lock sensors and rear brake anti-lock sensor signals.
- stoplight switch brake on/off signal.
- diagnostic data link.
Signal outputs are:
- instrument cluster ABS indicator.
- diagnostic data link.