Function

Function
The ABS control module -J104- is equipped with Diagnostic Trouble Code (DTC) memory and On Board Diagnostic (OBD) capability. The term On Board Diagnostic (OBD) refers to the electrical and electronic parts of ABS or ABS/EDL, i.e. only malfunctions related to the electrical parts regulated by the ABS control module are recognized. The control module can differentiate between 19 different malfunction sources.
The 26-pin ABS and ABS/EDL control module -J104- and the 31-pin ABS/EDL with TCS (ASR) -J104- control module is joined with the hydraulic unit to form a compact hydraulic module. The hydraulic module is located on the left side of the engine compartment. The Data Link Connector (DLC) is located below the instrument panel on the left side.
If the supply voltage drops below 10 Volts, the ABS system will switch off. All the relevant warning lights will light up. The system will switch on again as soon as the supply voltage increases to 10 Volts or above. The warning lights will go out. If the voltage fails completely due to an open-circuit or a blown fuse only the ABS warning light will be lit continuously.
The control module recognizes malfunctions during vehicle operation and stores them in a Diagnostic Trouble Code (DTC) memory. This information will remain available even if the system voltage fails.
Sporadic malfunctions will also be recognized and stored. But if these malfunctions do not occur again within the next 20 vehicle starts or during an extended journey, they will be erased from the DTC memory.
After switching the ignition on the ABS warning light -K47-, the traction control indicator light -K86- (only on vehicles with TCS) and the warning light for brake system -K118- light up for approximately 2 seconds.
During this procedure a test sequence (self-check) is run in the control module for the following functions:
- The voltage supply is checked (min. 10.0 V)
- The control module including the solenoid valve windings are checked.
- The wheel speed sensors are checked electrically; this check is not fully complete until the vehicle is driven for at least 30 seconds at a minimum of 60 Km/h (37 mph).
- The control module coding is checked.
The traction control system (TCS) is a vehicle safety system which prevents wheel spin during acceleration. The TCS also controls the engine braking (EBC). EBC prevents the wheels locking when the engine braking effect is high, e.g. when selecting a lower gear. The TCS is operational over the complete speed range. When the TCS is in the control mode the TCS warning light flashes 3 times per second,
The ABS control module -J104- is coded. New control modules obtained through the parts supply are not coded for vehicles with TCS.

VAG 1551 Scan Tool
The On Board Diagnostic (OBD) must be initiated at the beginning of troubleshooting. Electrical malfunctions which influence the braking characteristics will be stored. They can only be read with the VAG 1551 Scan Tool.
The DTC information displayed is used in conjunction with a DTC table which has information on the possible causes for pin-pointed repair measures.
From July 1996 the display group numbers are 3-digit (latest version of VAG 1551 program card).