ABS consists of two main subsystems: electrical and hydraulic. The electrical part of the system includes four wheel speed sensors, a control processor, and a set of connecting electrical wiring. The hydraulic part includes a pressure modulator, disc brake calipers, and hydraulic lines connecting the components.
The principle of the system operation is quite simple. Each wheel is equipped with an individual speed sensor. The sensor consists of a rotor (a ring with teeth evenly spaced along its perimeter) and a sensitive element in the form of a magnetized coil. The sensitive element of the sensor records the moments when the rotor teeth pass by it and converts the received information into electrical signals continuously transmitted to the ABS control processor. Based on the results of processing the incoming signals, the processor receives information about the relative rotation speed of each wheel. While all four wheels rotate at the same frequency, ABS is in a passive state. As soon as any of the wheels begins to lock, the processor records a change in the incoming signal and generates a command to trigger the modulator, which instantly releases the hydraulic fluid pressure in the brake mechanism of the corresponding wheel. As soon as normal wheel rotation is restored, the processor suspends the operation of the modulator.
In reality, the ABS operating scheme is much more complicated than it may seem, so the authors of this Guide do not recommend that car owners attempt to repair the system themselves. In case of problems, it would be wiser to contact car service specialists.
Reading ABS fault codes
When the engine is started, the ABS warning light on the dashboard should briefly come on and then go out again almost immediately. If, due to some malfunction, the light remains on after the engine is started, the ABS processor records the corresponding digital code in the memory of the self-diagnostic unit. The codes are read using a special scanner connected to the 16-pin diagnostic connector located under the front sill trim of the driver's door. If you do not have a scanner at hand, the car should be driven to a service station to have the memory read and the necessary repairs performed.
Below is an identification chart of ABS fault codes.
Note: Any restoration work should be performed by car service specialists.
| Code designation | Possible source of violation |
| 11 | Right front wheel sensor (open or short circuit in the circuit) |
| 12 | Right front wheel sensor (electrical interference or signal instability) |
| 13 | Left front wheel sensor (open or short circuit in the circuit) |
| 14 | Left front wheel sensor (electrical interference or signal instability) |
| 15 | Right rear wheel sensor (open or short circuit in the circuit) |
| 16 | Right rear wheel sensor (electrical interference or signal instability) |
| 17 | Left rear wheel sensor (open or short circuit in the circuit) |
| 18 | Left rear wheel sensor (electrical interference or signal instability) |
| 21 | Right Front Wheel Sensor Rotor |
| 22 | Left Front Wheel Sensor Rotor |
| 23 | Right rear wheel sensor rotor |
| 24 | Left rear wheel sensor rotor |
| 31 | Right Front Wheel Sensor Input Solenoid |
| 32 | Right Front Wheel Sensor Output Solenoid |
| 33 | Left Front Wheel Sensor Input Solenoid |
| 34 | Left Front Wheel Sensor Output Electromagnet |
| 35 | Right Rear Wheel Sensor Input Solenoid |
| 36 | Right rear wheel sensor output solenoid |
| 37 | Left Rear Wheel Sensor Input Solenoid |
| 38 | Left rear wheel sensor output solenoid |
| 41 | Right front wheel lock |
| 42 | Left front wheel lock |
| 43 | Right rear wheel lock |
| 44 | Left rear wheel lock |
| 51 | Engine blocking |
| 52 | The engine remains off |
| 53 | The motor remains on |
| 54 | Failure prevention relay |
| 61 | Ignition voltage too low |
| 62 | Excessively high ignition voltage |
| 71 | Tires of different diameters |
| 81 | Diagnostics of CPU and ROM/RAM units |
Clearing ABS CPU Memory
After eliminating the detected faults in the system, the processor memory must be cleared. To clear the memory, you will need a scanner again, if you do not have one at hand, the car will have to be driven to a service station. More detailed information on the scanner reader is given in Chapter Engine management.