12.2. General information on the anti-blocking brake system
The anti-blocking brake system is developed to provide maneuverability of the car, its stability on the road and the optimum mode of braking at emergence of a difficult road situation on any paving. The system controls the speed of rotation of wheels and operates pressure in the brake system in the course of braking. It prevents premature blocking of wheels.
The ABS system consists of three main components - sensors of speed of rotation of wheels, an electronic control unit and the control unit of hydraulics. Sensors (since 1985 - on one on each wheel, and on earlier models - on both forward wheels and one on back differential) send signals of various tension to the control unit which traces these signals, compares them to information put in the program and defines whether the wheel is going to be blocked. If this is so, then the control unit sends a signal to the control unit of hydraulics to reduce the liquid pressure (or any more not to raise it) in a brake support of this wheel. Modulation of pressure is made by means of electric valves of the solenoid.
If there is a malfunction in the system, on the dashboard the alarm lamp of "ABS" lights up. Sometimes the cause of defect of the ABS system can be defined visually. Attentively examine conducting of system. Pay special attention to conducting and connections at each wheel. Look for signs of attrition or other damages caused by the wrong laying of wires. If conducting of the wheel sensor is damaged, the sensor should be replaced (conducting and the sensor are inseparable).
DO NOT TRY to repair conducting of the ABS system. This system is sensitive to the slightest changes of resistance. Repair of conducting can change the size of resistance and lead to misoperation of system. If conducting of system is somehow damaged, it should be replaced.
Before shutdown or connection of any electric connections make sure that ignition is switched off.
Diagnostics and repair
If in the course of operation of the car on the dashboard was lit and remained included an alarm lamp, so it is necessary to pay attention to the ABS system. Though special test devices are necessary for the correct diagnostics of system, you can make several preliminary checks before sending the car to dealer office of service.
- Check the level of brake fluid in the tank.
- Check electric sockets of the electronic control device.
- Check electric sockets of the control device of hydraulics.
- Check safety locks.
- Check the conducting going to each forward and back wheel and make sure that all connections as it should be and conducting is not damaged.
If the above described preliminary check did not fix a problem, the car should be sent to dealer office of service for diagnostics. As this system is very difficult, its repair needs to be made only in dealer office of service.