5A4-6 ANTI-LOCK BRAKE SYSTEM (ABS) System Components The Anti-lock Brake System consists of a Electronic Hydraulic Control Unit (EHCU), four Wheel Speed Sensors and Warning Light. ABS Warning Light Electronic Hydraulic Control Unit (EHCU) The EHCU consists of Electronic Brake Control Module (EBCM) and Hydraulic Unit (HU). The EHCU is located at the frame side, in front of rear spring bracket. The EHCU consists of ABS control circuits, fault detector, and a fail-safe. It drives the hydraulic unit according to the signal from each sensor, cancelling ABS to return to normal braking when a malfunction has occurred in the ABS.
The EHCU is self-diagnosing function which can indicate faulty circuits during diagnosis. Vehicles equipped with the Anti-lock Brake System has an amber “ABS” warning light in the instrument panel. The “ABS” warning light will illuminate if a malfunction in the Anti-lock Brake System is detected by the Electronic Hydraulic Control Unit (EHCU). In case of an electronic malfunction, the EHCU will turn “ON” the “ABS” warning light and disable the Anti-lock braking function. The “ABS” light will turn “ON” for 2 seconds after the ignition switch is to the “ON” position, and then will go out.
If the “ABS” light comes “ON” and stays “ON” while driving, the Anti-lock Brake System should be inspected for a malfunction according to the diagnosis procedure. CONNECTOR EHCU Tang lock Push Push Lever Move lever outside Wheel Speed Sensor NOTE: It consists of a sensor and a rotor. The sensor is attached to the knuckle on the front wheels and to the bracket on the brake back plate on the rear wheels. The front speed sensor is coil type and rear is Hall IC type. The sensor rotors press-fitted to front and rear wheel hubs output pulse frequency depending on wheel rotation. The speed sensors find vehicle speed from its frequency.
When disconnecting harness connector from EHCU, push the tang lock of the connector ( portion) and release the tang lock. Then move the lever. Hydraulic Unit (HU) It consists of a Motor, Plunger Pump, Solenoid Valves and Check Valve. Solenoid Valves: Reduces or holds the caliper fluid pressure for each front disc brake or both rear drum brakes according to the signal sent from the EHCU. Reservoir: Temporarily holds the brake fluid that returns from the front and rear wheel brake so that pressure of front wheel brake can be reduced smoothly. Plunger Pump: Feeds the brake fluid held in the reservoir to the master cylinder. Motor: Drives the pump according to the signal from EHCU. Check Valve:
Controls the brake fluid flow. Normal and Anti-lock Braking Under normal driving conditions, the Anti-lock Brake System functions the same as a standard power assisted brake system. However, with the detection of wheel lock-up, a slight bump or kick-back will be felt in the brake pedal. This pedal “bump” will be followed by a series of short pedal pulsations which occurs in rapid succession. The brake pedal pulsation will continue