Audi Workshop Service and Repair Manuals

The control unit of a system with self-diagnosis function detects faults and malfunctions during vehicle operation and stores them in a permanent memory, the contents of which remain intact if the voltage supply from the battery is interrupted.

The self - diagnosis function relates to the electrical and electronic parts of the ABS, i.e. it only registers faults via the electrical connection to the control unit (e.g. speed sensor open circuit).

The self-diagnosis function enables faults to be traced quickly and efficiently. The self-diagnosis options can be utilised with the aid of fault reader V.A.G 1551/1552 or vehicle system tester VAS 5051. To do this the control unit of the system concerned must be able to exchange data with the fault reader. They must communicate with each other.

The diagnostic connector is the interface for communication between the control unit and the fault reader.

To start the fault finding procedure, connect the fault reader to the diagnostic connector. Establish the communication link with the control unit of the system concerned,

When the communication link has been established, the required fault finding functions provided by the on-board system you are testing can be selected. These functions are programmed in the form of fixed diagnosis routines. Their use is described in the relevant sections of this Workshop Manual. After first checking the control unit version, start with function 02 "Interrogate fault memory"

Any faults which may be stored in the memory will be indicated on the display of the fault reader. The information displayed can then be used in conjunction with fault tables which enable the cause of the fault to be traced and the necessary repair to be performed quickly and efficiently. The fault tables can be found in the relevant sections of this Workshop Manual.

The self-diagnosis function distinguishes between "static" and "sporadic" faults. If a fault which has been stored in the memory as a "static" fault is no longer present when the ignition is switched on, it is converted into a "sporadic" fault.

Sporadic faults are identified as such. "/SP" appears on the right of the tester display.

A sporadic fault is erased automatically if it no longer occurs over a certain number of driving cycles.

Static faults remain stored in the fault memory until the memory is erased with the fault reader.

If the control unit has to be renewed, first check the control unit version. This appears on the display of the fault reader together with the code when communication is established between control unit and fault reader.