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 wiring. The hydraulic part includes a pressure modulator, disc brake calipers and hydraulic lines connecting the components.
The principle of operation of the system is quite simple. Each of the wheels is equipped with an individual speed sensor. The sensor consists of a rotor (rings with teeth evenly spaced around its perimeter) and a sensitive element in the form of a magnetized coil. The sensitive element of the sensor captures the moments of the passage of the teeth of the rotor and converts the information received into electrical signals that are continuously transmitted to the ABS control processor. Based on the results of processing the incoming signals, the processor receives information about the relative speed of rotation of each of the wheels. As long as all four wheels rotate at the same speed, ABS is in a passive state. As soon as any of the wheels starts to block, the processor detects a change in the input signal and generates a command to operate the modulator, which instantly relieves the pressure of the hydraulic fluid in the brake mechanism of the corresponding wheel. As soon as normal rotation of the wheel is restored, the processor suspends the functioning of the modulator.
In reality, the ABS operation is much more complicated than it might seem, so the compilers of this manual do not recommend car owners to attempt to repair the system on their own. In the event of a problem, it would be wiser to contact a car service specialist.
Reading ABS Fault Codes
When starting the engine, the ABS warning lamp on the instrument panel of the vehicle should turn on briefly and go out again almost immediately. If, due to any violation, the lamp remains on after the engine is started, the ABS processor writes the corresponding digital code to the memory of the self-diagnosis unit. Codes are read using a special scanner connected to a 16-pin diagnostic connector located under the front sill of the driver's door of the car. In the absence of a scanner at hand, the car should be driven away to read the memory and perform the necessary restoration repairs to a service station.
Below is an ABS trouble code identification card.
Note. Any repair work should be carried out by an authorized service center.
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 stability disturbance) |
13 | Left front wheel sensor (open or short circuit in the circuit) |
14 | Left front wheel sensor (electrical interference or signal stability disturbance) |
15 | Right rear wheel sensor (open or short circuit in the circuit) |
16 | Right rear wheel sensor (electrical interference or signal stability disturbance) |
17 | Left rear wheel sensor (open or short circuit in the circuit) |
18 | Left rear wheel sensor (electrical interference or signal stability disturbance) |
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 solenoid |
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 | Motor lock |
52 | Motor stays off |
53 | Motor stays on |
54 | Fault Prevention Relay |
61 | Excessively low ignition voltage |
62 | Excessively high ignition voltage |
71 | Tires of various diameters |
81 | Diagnostics of CPU and ROM/RAM blocks |
Clearing ABS memory
After fixing the identified problems in the system, the processor memory should be cleared. To clear the memory, you will again need a scanner, in the absence of which the car will have to be driven to a service station. For more information on the scanner reader, see Chapter Engine management.