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 varying voltages to the control unit, which monitors these signals, compares them with the information stored in the program, and determines whether the wheel is about to lock. If so, the control unit sends a signal to the hydraulic control unit to reduce the fluid pressure (or don't raise it anymore) in the brake caliper of this wheel. Pressure modulation is performed by means of electric solenoid valves.
If a fault occurs within the system itself, the "ABS" warning light on the instrument panel will come on. Sometimes the cause of the ABS system malfunction can be determined visually. Carefully inspect the system wiring. Pay particular attention to the wiring and connections at each wheel. Look for signs of abrasion or other damage caused by improper wiring. If the wheel sensor wiring is damaged, the sensor should be replaced (the wiring and the sensor are inseparable).
DO NOT attempt to repair the ABS wiring. The system is sensitive to the slightest change in resistance. Repairing the wiring may change the resistance value and cause the system to not operate properly. If the system wiring is damaged in any way, it must be replaced.
Before disconnecting or connecting any electrical connections, make sure the ignition is off.
Diagnostics and repair
If the warning light on the dashboard lights up and stays on while the car is running, it means you should pay attention to the ABS system. Although special test equipment is needed to properly diagnose the system, you can do a few preliminary checks before sending the car to the dealer service department.
- Check the brake fluid level in the reservoir.
- Check the electrical connectors of the electronic control unit.
- Check the electrical connectors of the hydraulic control device.
- Check the 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 solve the problem, the car should be sent to the dealer service department for diagnostics. Since this system is very complex, its repair should be carried out only at the dealer service department.