Anti-lock Brake System (ABS) — General Information and Error Codes (Opel Corsa B)

General information

The anti-lock braking system (ABS) is an optional extra on the models in question.

When a vehicle is equipped with a conventional braking system, abruptly pressing the foot brake pedal causes the wheels to lock. This disrupts the tread's grip on the road surface and the vehicle may skid, causing it to lose control. The anti-lock braking system (ABS) prevents premature wheel locking by continuously controlling the speed of the wheels during braking by modulating the hydraulic fluid pressure in each brake mechanism.

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.

ABS system components



The principle of the system's operation is quite simple. Each wheel is equipped with an individual speed sensor. The sensor consists of a rotor (rings with teeth evenly spaced around their 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 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 rotation speed of each of the wheels. While all four wheels rotate at the same frequency, the 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 pressure of the hydraulic fluid in the brake mechanism of the corresponding wheel. Immediately after the normal rotation of the wheel is restored, the processor suspends the operation of the modulator.



Operating principle of ABS brake circuit parallel configuration



Operating principle of ABS brake circuit of diagonal configuration





In order to prevent false signals from affecting the ABS operation, a special safety circuit is built into its control system. When an inadequate signal is received by the control unit, as well as when the supply voltage level drops excessively, the system is automatically switched off, and the ABS control lamp lights up on the instrument panel (see Chapter Controls and operating techniques at the beginning of the Manual). The braking system continues to function normally.

In reality, the ABS system operation scheme is much more complex than it may seem, so the authors of this Manual do not recommend that car owners attempt to repair the system themselves. In the event of problems, it would be most reasonable to contact a car service specialist, where the appropriate diagnostics will be performed using a scanner reader connected to the DLC connector (see Chapter Fuel, exhaust and emission control systems).

Reading ABS fault codes

When the engine is started, the ABS warning lamp on the vehicle instrument panel should briefly come on and then go out again almost immediately. If, due to some malfunction, the lamp remains on after the engine has been 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 a scanner is not available, the vehicle should be taken to a service station for memory reading and the necessary repair work. The identification card of ABS diagnostic codes is provided in the Specifications of Chapter Brake system.

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 electrical systems.