Volkswagen Workshop Service and Repair Manuals

The ABS control unit (J104) is located on left under the rear seat. It is equipped with a fault memory. The diagnostic connections are located under a cover on right in front of dash panel.

The term self diagnosis relates to the electrical/electronic part of the ABS or ABS/EDL; in other words only faults via the electrical connection to the control unit are recognised (e.g. valve open circuit).

The control unit recognises faults and malfunctions during ABS or ABS/EDL operation and stores them in a permanent memory, the contents of which can be retrieved years later despite the lack of battery voltage.

Faults which occur sporadically (isolated) are also recognised and stored but, in contrast to other systems capable of diagnosis, without the addendum "SP" (sporadic).

Faults are stored with differing priorities: Solenoid valve faults have the highest, while faults which occur sporadically have the lowest priority.

After switching on the ignition the ABS warning lamp (K47) lights up for approx. 2 seconds.

A test sequence is run in the control unit with the following functions:

• ◆ Hydraulic pump run-up at low speed
• ◆ A brief valve activation after switching on the ignition

If an ABS fault is stored, the ABS is switched off, and the warning lamp (K47) remains on.

If an EDL fault is stored, the EDL system is switched off. A warning via the warning lamp (K47) does not occur.

If the ABS or ABS/EDL is switched off because a fault is registered, the conventional hydraulic brake system remains fully operative.

The self diagnosis must be initiated at the commencement of fault finding and the stored information interrogated with the

Fault reader V.A.G 1551

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

The procedure for self diagnosis, Fault finding and repair for the ABS and ABS/EDL is identical.

Both systems have control units equipped with 55 pins. The self diagnosis operates in the rapid data transfer mode.

With the exception of the additional contacts for the electronic differential lock, the contact assignment of the control unit (J104) connector (55 pin) are identical for both systems.

When performing the electrical check on vehicles with ABS, carry out all test steps not marked EDL.

For vehicles equipped with ABS/EDL carry out all test steps.