Control Module

NOTE: For model name/model number cross reference refer to Model Designation Table. Application and ID







Model 129 (except 129.058/063) and 202, located On the right side of the engine compartment.





The control unit installed in Models 129.058/063. 140 and 202 includes a fault memory. On Models 129 and 140 this is located in the module box. For information on diagnosis and test program see Testing and inspection.

The Control unit processes the signals from the wheel speed sensors and controls the valves in the hydraulic unit.

The entire signal conditioning and signal processing is digital.

The control unit is connected to the ABS main cable harness via a 35 pole plug connection. The electronic control unit is functionally divided into:
^ The Signal Conditioning Section
^ The Logic Section
^ The Safety Circuit
^ Fault Memory (Model 129.058/063, 140, 202)

Signal Conditioning Section
In the Signal conditioning section the signals supplied by the wheel speed sensors are converted into 8 form suitable for use by the logic section.

To prevent problems while measuring the wheel speed, which may be caused by production tolerances and by movements in the steering knuckle, the input signals are filtered prior to use. Deceleration and acceleration signals obtained from the wheel speed signals are processed in the logic section.

Logic Section
The logic section of the ABS control unit employs the following input signals for each controlled wheel or the controlled rear wheels:
Wheel Slip
Wheel Speed Acceleration
Wheel Deceleration

Output signals from the logic section control the solenoid valves of the hydraulic unit. As a result, the following hydraulic functions can be generated in the brake calipers of the wheel brakes:
Pressure Build-Up
Pressure Holding
Pressure Reduction

Safety Circuit
The safety circuit has the job of recognizing faulty signals in the ABS control unit and faults outside the ABS control unit in the electrical installation. In addition, the safety circuit intervenes in the control sequence during extreme driving conditions such as aquaplaning. When a fault is recognized, the system should be switched off, a condition which is indicated to the driver by the ABS malfunction indicator lamp coming on.

The safety circuit continuously monitors the battery voltage. If the voltage is below specific requirements (11 V) the system is also switched off until the voltage returns to the specified range.

In addition to monitoring operation, the safety circuit also incorporates an active component, a test cycle with the designation Built In Test Equipment (BITE).

The test cycle begins as soon as the wheel speed in all three speed channels is higher than 5-7 km/h. The cycle is activated by the wheel speed sensor voltage, which is monitored automatically at the same time. The test cycle itself checks parts of the monitoring circuit as well as the logic section. For this purpose, the electronic control unit is fed with the specific test sample signals to check whether the correct output signals are available.

Fault Memory
The control unit installed an Models 129. 058/063, 140 and 202 incorporates a fault memory and is thus suitable for fault diagnosis. Recorded errors remain stored even when the battery cable is disconnected.