Function

Function
As the control modules are interconnected with a data bus wire, always start troubleshooting by checking Diagnostic Trouble Code (DTC) memories of all the control modules in the vehicle.

This occurs in "Automatic test sequence" and is activated with key function 00.

When doing this, check to determine if there are DTCs stored which may influence the ABS.

The 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 47-pin ABS Control Module (w/EDL) -J104- forms a compact assembly with the hydraulic unit. The unit is located on the left in the engine compartment. The control module is equipped with a DTC memory. The Data Link Connector (DLC) is located left of the steering column under the instrument panel. On early production cars the DLC is in the center console below the heating and 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 (irregular) malfunctions will also be recognized and stored. But if faults affecting the data bus system do not occur again within the next 15 vehicle start and driving off sequences, or other malfunctions within the next 50 vehicle start and driving off sequences, they will be erased from DTC memory except for the malfunction "Control module faulty" (forget malfunction counter).

After the ignition is switched on and/or the engine is started, the ABS warning light -K47- and the ASR/ESP control lamp K155- will light up forapprox. 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 the wheel speed signal is not OK after the car has been driven and a speed of approx. 20 km/h (approx. 13 mph) has been exceeded, the ABS warning light -K47- will light up again.

Special detail for bleeding brake systems with ABS/EDL

If a chamber in the brake fluid reservoir has run empty, basic setting must be performed for bleeding the brakes.

V.A.G 1551 scan tool or tester VAS 5051

The On Board Diagnostic must be initiated 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, Vehicles system tester V.A.G 1552 or Vehicle Diagnosis, Testing and Information System VAS 5051.

As a minimum requirement, program card level 9.0 must be installed in V.A.G 1551 scan tool and program card level 6.0 installed in vehicle systems tester V.A.G 1552.