Function

On Board Diagnosis (OBD) function ITT Mark 20 IE
Function
Since control modules are interconnected with a Controller Area Network bus (CAN-bus), always start (OBD) by pressing buttons -0 and -0- to insert "Automatic test sequence" address word 00. This checks Diagnostic Trouble Code (DTC) memory for all control modules in the vehicle, including those that may influence the ABS System in case of malfunction of all DTC memories. Therefore, all ABS related control modules are checked for DTCs.
On-Board Diagnosis (OBD) relates to the electrical/electronic part of ABS. In other words, only DTCs via electrical connection to the control module are recognized (e.g. speed sensor open circuit).
The 25 pin ABS Control Module -J104- and the ABS hydraulic unit together form a compact module. The module is located on the left side of the engine compartment. The Control module is equipped with a DTC memory. The On Board Diagnostic Data Link Connection (DLC) is located in the center console below heating/air conditioning controls.
The control module recognizes DTCs during vehicle operation and stores them in a permanent memory. The contents remain with out battery voltage.
Sporadic DTCs will also be recognized and stored. But if these DTCs do not occur again within the next 50 vehicle starts and driving off sequences then, with the exception of "control module inoperative", the DTCs will be erased.
After switching on the ignition and/or starting the engine ABS warning light -K47- and warning light for brake system -K118- illuminate for approx. 2 seconds.
During this period a test sequence (OBD) is run in the control module for the following functions:
^ Voltage supply is checked, at least 10.0 Volts
^ Control module, including valve windings (coils), are checked
^ Speed sensor (electrical) check is performed; completed at 20 km/h (approx. 13 mph)
^ Control module code is checked

Scan Tool VAG 1551
On-Board Diagnosis (OBD) must be initiated at beginning of the Diagnostic Trouble Codes (DTC check. Electrical DTCs which influence braking characteristics will be stored. They can only be checked with VAG 1551 scan tool.
Displayed Diagnostic Trouble Codes are used in conjunction with a DTC table which has information on possible DTC causes for pinpointed repair procedures.