General information
1. In a conventional braking system, when you press the brake pedal hard, the wheels lock up (that is, they stop rotating) and the car becomes uncontrollable. The anti-lock braking system (ABS) is designed to prevent the wheels from locking. This effect is achieved by briefly reducing the 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 disks and inductive converters, a control unit (figure 2.2,a) and electrical wires connecting the system components. The hydraulic part of the system consists of a block of hydraulic actuators (figure 2.2,b). wheel cylinders and the pipes connecting these components.
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3. In principle, the ABS works very simply: wheel sensors monitor the rotational speed of the wheels and transmit this information to the control unit (figure 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 that wheel begins to differ from the signals from the other sensors. This is how the control unit "learns" about the blocking of one of the car's wheels. At the same time, 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 rotation speed begins to match the rotation speed of the other wheels, the signal from the sensor of this wheel also begins to match the signals from the sensors of the other wheels. At this point, the ABS is switched off again.
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4. In fact, the ABS system is much more complex and we do not recommend that you diagnose and repair this system yourself. If your vehicle's anti-lock braking system is faulty, contact a specialist service station.
Anti-lock braking system fault codes
5. When the engine starts, the ABS warning light on the dashboard should come on and then go out. 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 control unit memory can be done in two ways. Models produced from 1993 to 1997 have a data link connector (DLC) located in the engine compartment for this purpose. In models produced since 1998, a special scanner is connected to a 16-pin connector located in the vehicle interior. If you do not have this scanner, fault codes can be retrieved using a code reader available at dealers and some service stations.
6. In models produced from 1993 to 1997, access to the ABS control unit self-diagnosis system is carried out as follows. In the data transfer connector, short-circuit the FBS and GND terminals. Also, connect a voltmeter to the TBS terminals and the vehicle body (to any grounding point) (figure 2.6). Turn the ignition key to the ON position (but don't start the engine) and watch the fluctuations of the voltmeter needle. For this purpose you will need an arrow-type voltmeter. Make sure the battery voltage is at least 11 V, the gear shift lever is in neutral, all electrical consumers are turned off, the throttle is closed, and the engine is warmed up to operating temperature.
7. Error codes are determined by counting the oscillations of the voltmeter needle. If there are no fault codes, the ABS warning light should come on and immediately go out. If there are fault codes in the control unit's memory, the warning lamp will indicate their meaning using a series of flashes. For example, fault code 22 (electromagnetic 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 carried out by a dealer or a specialized service station.
9. Reading fault codes in models produced since 1998 is carried out using a special scanner. Additional information on hardware and fault codes is provided in chapter 6. Troubleshooting should be carried out by a dealer or a specialized service station.
10. After the fault has been corrected, its code should be deleted from the control unit memory. Fault codes can be erased from the control unit memory only using a scanner. If you do not have a scanner, please contact a specialized service station. Additional information on hardware and fault codes is provided in chapter 6.
ABS system error codes
