The ABS system consists of three main components - wheel speed sensors, an electronic control unit and a hydraulic control unit. Sensors (since 1985, one on each wheel, and on earlier models, on both front wheels and one on the rear differential) send signals of various voltages to the control unit, which monitors these signals, compares them with the information embedded in the program, and determines if the wheel is about to lock up. If so, the control unit sends a signal to the hydraulic control unit to reduce fluid pressure (or don't raise it anymore) in the brake caliper of that wheel. Pressure modulation is done by electric solenoid valves.
If a malfunction occurs within the system itself, a warning lamp lights up on the instrument panel «ABS». Sometimes the cause of an ABS system malfunction can be determined visually. Carefully inspect the system wiring. Pay special attention to the wiring and connections at each wheel. Look for signs of fraying or other damage caused by improper wiring. If the wheel sensor wiring is damaged, the sensor should be replaced (wiring and sensor are inseparable).
DO NOT attempt to repair the ABS wiring. This system is sensitive to the slightest changes in resistance. Wiring repairs can change the resistance value and cause the system to malfunction. If the system wiring is damaged in any way, it should be replaced.
Make sure the ignition is off before disconnecting or connecting any electrical connections.
Diagnostics and repair
If during the operation of the car on the instrument panel the signal lamp lights up and remains on, then you should pay attention to the ABS system. Although special test tools are needed to properly diagnose the system, there are a few preliminary checks you can make before taking your vehicle to the dealership for service.
- Check the brake fluid level in the reservoir.
- Check the electrical connectors of the electronic control device.
- Check the electrical connectors of the hydraulic control device.
- Check fuses.
- Check the wiring going to each front and rear wheel and make sure all connections are good and the wiring is not damaged.
If the above preliminary check does not correct the problem, the vehicle should be sent to the dealer service department for diagnosis. Since this system is very complex, its repair must be carried out only in the dealer service department.