Drivers Information

General
There is a system malfunction indicator lamp for the ABS in the instrument cluster.

Switching On The Ignition And Starting The Engine
When the ignition is switched on (ignition/starter switch in position "2"), the malfunction indicator lamp in the instrument cluster comes on (bulb check) and goes out when the engine is running. If the ABS malfunction indicator lamp comes on when the engine is running, there is a fault in the ABS.

The system is inoperative, but the full braking effect of the braking system is retained without blockage protection.

Driving Mode
The system carries out a self-check after starting off. At the same time the return pump in the hydraulic unit also starts up briefly (may sometimes be felt at the brake pedal). If a fault is found in the process, the ABS malfunction indicator lamp comes on again. System faults which occur while driving also cause the ABS malfunction indicator lamp to come on constantly.

If the ABS malfunction indicator lamp comes on while driving and goes out again after a short time, the cause is battery undervoltage

ABS is ready for operation when the vehicle has exceeded a speed of 8 km/h after starting off. A control is possible down to a speed of 3 km/h.

The speeds of the front are recorded and processed separately in the ABS control module (N47-7). The mean speed of the rear wheels is taken from the drive pinion of the rear axle center assembly.

A reference speed which represents the approximate vehicle speed is calculated by linking the individual wheel speeds. Slip signals are derived from comparing the wheel speed and reference speed.

The ABS control mode starts if the ABS control module (N47-7) recognizes from the wheel speed signals that one or more wheels is tending to lock when braking.

Initially the brake pressure is kept constant (an increase in brake pressure is prevented). If a tendency to lock continues, the brake pressure is reduced (brake fluid is pumped back) until the wheel starts to accelerate again. After that the brake pressure is kept constant again. If the continued acceleration of a wheel exceeds a set value, a pressure increase is permitted again.

These control processes repeat continuously during ABS braking until the brake pedal is released or down to a speed of 3 km/h.