GF42.30-D-0003H Anti-Lock Brake System (ABS) Function

GF42.30-D-0003H Anti-lock Brake System (ABS) Function


The antilock brake system (ABS) prevents the wheels locking when braking so that the vehicle continues to remain steerable. It operates independently of the road surface as of a speed of approx. 8 km/h. By evaluating the signals from the following sensors the ESP control unit (N30/4), detects that the criteria for an ABS control exist:

^ Stop light switch (S9/1)
^ Left front rpm sensor (L6/1)
^ Right front rpm sensor (L6/2)
^ Left rear rpm sensor (L6/3)
^ Right rear rpm sensor (L6/4)
^ Brake pressure sensor is integrated in the traction system hydraulic unit

ABS control mode

If for example a wheel tends to lock while braking, the brake pressure in this wheel brake is regulated by the ESP control unit via the traction system hydraulic unit until the brake application is concluded

The control takes place in the following 3 control phases:

^ Pressure build-up
^ Pressure holding
^ Pressure reduction

To do this the solenoid valves in the traction system hydraulic unit is actuated by the ESP control unit. The brake force at the slip limit is modulated by the ABS.

The ABS cuts in if one of the following conditions exist:

^ ABS is enabled once the engine starts "circuit 61 ON" and once self-diagnosis has taken place if no fault is present
^ The vehicle speed after starting off is > 8 km/h
^ Criteria for ABS control exist

The ABS is switched off if one of the following conditions is given:

^ The vehicle speed is < 3 km/h
^ Brake application finished, detection via stop lamp switch and brake pressure sensor
^ An ABS malfunction exists