The ABS safety lamp lights for approx. 2 seconds (lamp check) as from ignition lock position 2 and then goes out if no faults are found in the ABS system.
If the ABS safety circuits detects a fault, the ABS systems is deactivated and the ABS safety lamp lights.
If the fault no longer applies during the next start procedure, the lamp will go out after the lamp check.
Note
The ABS safety lamp is permanently activated during diagnosis (communication with the tester).
The DME main relay provides the positive supply of the control unit as of ignition lock position 2. The voltage is retained for approx. 5 seconds after "ignition OFF" (DME holding circuit).
The ground supply is produced via two ground lines.
The ABS control unit acquires the wheel speed signals via the four speed sensors, processes the signals and then makes them available for other users such as the IKE (speedometer signal) or the EDC.
The speed output signals are square-wave signals with constant amplitude (low level < 1 V, high level > 11 V). The frequency is dependent on the wheel speeds and is within the range from 0 to 1700 Hz (0 to 250 km/h).
The brake light switch signal serves as a redundant signal for recognizing an initiated braking procedure. This enables improvements in control comfort.
Faults in the brake light switch circuit are stored in the fault code memory, however, the ABS safety lamp is not activated when such faults occur.