On Board Diagnostic (OBD)

ABS ITT Mark 20 IE On Board Diagnostic (ODD)

Function
Since the control modules are interconnected with CAN-bus, always begin OBD by checking the Diagnostic Trouble Code (DTC) memories of all the control modules in the vehicle.

This occurs in the Automatic test sequence and is activated with key function 00.
When doing this, check to see if there are DTCs stored which may influence the ABS.

On Board Diagnostic (OBD) relates to the electrical/electronic part of the ABS, i.e. only malfunctions via the electrical connection to the control module are recognized (e.g. speed sensor open circuit).

The 25-pin ABS Control Module (w/EDL) -J104-forms with the hydraulic unit a compact unit. The unit is located on the left in the engine compartment. The control module is equipped with a DTC memory. The diagnostic connection is located in the center console below the heating/air conditioning controls.

The control module recognizes malfunctions during vehicle operation and stores them in a permanent memory, the contents of which remain even during periods of no battery voltage.

Sporadic (isolated) malfunctions will also be recognized and stored. But if these malfunctions do not occur again within the next 50 vehicle starts and driving off sequences then, with the exception of "control module inoperative", the DTC memory will be erased.

After switching on the ignition and/or starting the engine the ABS warning light -K47- and the warning light for brake system -K118- light up for approximately 2 seconds.

During this period a test sequence (self-check) is run in the control module for the following functions:
- To check if the supply voltage is at least 10.0 Volt
- To check control module including the valve windings
- To check the coding of the control module
- A static check of the speed sensor (no speed signal)
- If after driving off and exceeding a speed of approximately 20 km/h (approximately 13 mph) the speed signal is not OK. The ABS warning light -K47 will light up again.

V.A.G 1551 Scan Tool or tester VAS 5051
The On Board Diagnostic (OBD) must be initiated always at the commencement of troubleshooting. Electrical malfunctions which influence the braking characteristics will be stored. They can be checked with the V.A.G 1551 Scan Tool or with the tester VAS 5051.

The information displayed is used in conjunction with a DTC table which has information on the possible DTC causes for repair measures.