General information
1. In a conventional brake system, pressing the brake pedal hard will lock the wheels (i.e. stop spinning) and the car becomes uncontrollable. Anti-lock braking system (ABS) Designed to prevent wheel lock. This effect is achieved due to a short-term decrease in pressure in the wheel brake cylinders (the pressure in the cylinders becomes not constant, but pulsating).
2. ABS consists of two main systems: electrical and hydraulic. The electrical part of the system consists of four wheel sensors with toothed discs and induction transducers, a control unit (pic. 2.2,a) and electrical wires connecting system components. The hydraulic part of the system consists of a block of hydraulic actuators (pic. 2.2b). wheel cylinders and pipelines connecting these components.
3. In principle, the operation of the ABS is very simple: wheel sensors monitor the speed of the wheels and transmit this information to the control unit (pic. 2.3, a, b). The control unit constantly compares the signals from these sensors. As long as the signals do not differ from each other, the system remains passive. However, if one of the wheels slows down, the signal from the sensor of this wheel begins to differ from the signals of other sensors. So the control unit "learns" about blocking one of the wheels of the car. In this case, the control unit sends a signal to the hydraulic actuator, which reduces the pressure of the brake fluid in the wheel cylinder of the locked wheel. As soon as the wheel is unlocked and its speed begins to coincide with the speed of the other wheels, the signal from the sensor of this wheel also begins to coincide with the signals of the sensors of the other wheels. At this point, the ABS is switched off again.
4. In fact, the ABS system is much more complicated and we do not recommend you to diagnose and repair this system yourself. If the anti-lock braking system of your car is faulty, contact a specialized service station.
Anti-Lock Braking System Fault Codes
5. When starting the engine, the ABS warning light on the dashboard should light up and then turn off. However, under certain conditions, the light remains on. In this case, a fault code remains in the memory of the ABS control unit. Reading fault codes from the memory of the control unit can be done in two ways. Models manufactured from 1993 to 1997 have a data connector for this purpose (DLC). located in the engine compartment. In models produced since 1998, a special scanner is connected to a 16-pin connector located in the car. If you do not have this scanner, trouble codes can be retrieved using a code reader available from dealers and some service stations.
6. In models manufactured from 1993 to 1997, access to the self-diagnosis system of the ABS control unit is carried out as follows. In the data connector, bridge the FBS and GND terminals. In addition, connect a voltmeter to the TBS terminals and the car body (to any ground point) (pic. 2.6). Turn the ignition key to the ON position (but don't start the engine) and watch the voltmeter fluctuate. For this purpose, you will need a pointer-type voltmeter. Verify that the battery voltage is at least 11 V. The shift lever is in neutral, all electrical consumers are off, the throttle is closed, and the engine is at operating temperature.
7. Fault codes are determined by counting the oscillations of the voltmeter needle. If there are no trouble codes, the ABS warning light should come on and go out immediately. If there are fault codes in the memory of the control unit, the warning lamp will give their values with a series of flashes. For example, fault code 22 (solenoid valve) is indicated as follows; two long flashes, then a pause, then two short flashes.
8. Below is a breakdown of the most common ABS fault codes. Troubleshooting should be done at the dealer or a specialized service station.
9. Reading fault codes in models manufactured since 1998 is carried out using a special scanner. For more information about hardware and fault codes, see chapter 6. Troubleshooting should be done at the dealer or a specialized service station.
10. After the malfunction has been eliminated, its code should be deleted from the memory of the control unit. Fault codes are erased from the memory of the control unit only with the help of a scanner. If you do not have a scanner, contact a specialized service station. For more information about hardware and fault codes, see chapter 6.