Opel Corsa B 1993–2000 Service and Repair Manual: Anti-lock braking system (ABS) - general information

The anti-lock braking system (ABS) is available as an option on most models from 1989. The system monitors the rotational speed of each wheel and prevents lock-up during braking by reducing the hydraulic pressure to any wheel cylinder or caliper where lock-up is occurring. This is particularly valuable when braking on loose or slippery surfaces, or during emergency braking when steering corrections may also be taking place.

However the system will not protect against skids caused by excessively fast cornering or heavy acceleration on poor surfaces.

The main components of the system are shown in illustration. Magnetic pulses are induced in the wheel speed sensors by a toothed disc which is part of the brake disc or drum. The pulses are monitored by the electronic control unit (ECU). The ECU alters the hydraulic pressure when necessary by means of solenoid valves located in the hydraulic unit. An electric pump in the hydraulic unit generates the hydraulic pressure, which is higher than that which would be produced by the master cylinder alone.

In use, the onset of the anti-lock function is indicated to the driver by a pulsating of the brake pedal. Any malfunction in the system is indicated by a warning light on the instrument panel. When the system is working correctly, the warning light will illuminate for a few seconds when the ignition is switched on, but will then go out and remain out. If it comes on during driving, there is a fault. Normal braking is not affected by malfunction of the ABS.

The ECU is mounted under the facia on the left-hand side. It is protected against voltage surges by a surge arrester relay and fuse mounted together under the bonnet. The ECU has its own fault diagnosis program, but this is only accessible to Vauxhall dealers or other specialists with the necessary test equipment.

No routine maintenance of the ABS components is required. The hydraulic pipes and unions must be inspected for condition and security in the same way as any other part of the brake hydraulic system Note that the ECU is electrically fragile and should be treated with the same precautions as the fuel injection system control unit.

Main components of the ABS

1. Front wheel speed sensors
2. Rear wheel speed sensors
3. Master cylinder
4. Servo
5. Hydraulic unit
6. Electronic control unit
7. Brake proportioning valves
8. Diagnostic Plug