Electronic Control

The ABS electronic control unit is based on digital technology and contains the following functional zones:

^ Speed Processing
^ Two Microprocessors
^ Monitoring
^ Fault Memory
^ Output Stages for Valves and Pump

The control unit monitors the wheel speed sensor signals and derives from these signals the amount of wheel slip at each wheel. If wheel lock is impending at any wheel during braking, ABS regulation of the appropriate hydraulic circuit is initiated.

The control unit incorporates extensive safety monitoring with self-diagnostic capabilities. When the ignition is switched ON, the control unit performs a self-test. The ABS indicator lamp is illuminated for approximately two seconds. The internal circuits of the control unit are checked, as are external circuits such as the wheel sensors, pedal travel sensor, and voltage supply. When the engine is running and the vehicle begins to move (as detected by wheel sensor signals), the solenoid valves and pump rnotor are energized briefly as a dynamic test.

If a fault is detected, the ABS switches OFF. The ABS indicator lamp is illuminated and the fault is stored in the fault memory.

The ABS control unit is connected to the diagnostic link, and troubleshooting is carried out with the BMW Service Test or MoDiC, using the appropriate software, and with the diagnostic manual for E36 vehicles.


Comparison of E30 and E36


Characteristic E30 E36

Three Channel System Y Y

"Select-Low" Regulation of Rear Brakes Y Y

"Closed" System Y N

"Open" System N Y

Four Wheel Sensors Y Y

Three Phase Control Y Y

Valve and Pump Relays on Hydraulic Unit Y N

ABS and Pump Relay in Power Distribution Box N Y

Brake Pedal Travel Sensor N Y

Pump Speed Sensor N Y

Three Valve Hydraulic Unit Y N

Six Valve Hydraulic Unit N Y

Pump Cycled On and Off According to Pedal Travel N Y

Fault Memory N Y

Diagnostic Link N Y


Y = Yes; N = No