ABS Control Module, Function

Function of ABS Control Module

MODEL 202 as of 1.9.95,
168, 170, 208 with CODE (470a) Anti-lock braking system (ABS)




The ABS control module is divided up into the following functions:
- Signal conditioning
- Logic section
- Safety circuit

Signal conditioning
The following input signals are conditioned for the logic section:

- 3 speed sensors (models 170, 202, 208)
4 speed sensors (model 168)
- Stop lamp switch (4-pin) (S9/1)

Logic section
The conditioned signals are processed in the logic section and converted into output signals.

Speed signals:
The conditioned speed signals are continuously compared with each other and then with the preset slip thresholds (differential speeds between the front and rear wheels, depending on vehicle speed).
The following variables are determined by way of this comparison
- Brake slip
- Wheel acceleration
- Front wheel driving speed
- Curve recognition

An ABS control mode is initiated if the variables determined exceed the preset slip thresholds.

Stop lamp switch signal:
A signal is transmitted to the logic section when the brake is operated. The control module recognizes the braking process.

Safety circuit
The task of the safety circuit is to recognize defective signals in the control module and faults in the electric cable system. The actuation of the solenoid valves and the return pump is monitored during the control process. If a fault is recognized, the system is switched off and this is displayed to the driver by the ABS malfunction indicator lamp (A1e17) coming on. A fault code is also stored in the control module.

In addition the safety circuit continuously monitors battery voltage. If the voltage falls below 10 V or exceeds 18-20 V, the system is also switched off again until the voltage is in the specified range again.