On Board Diagnostic (OBD) for ABS and ESP, general notes: Notes

This Manual is intended as a practical aid for technicians and electricians in the workshop when working on the Audi A6 and dealing with malfunctions and problems reported by the customer.

If the malfunction is related to one of the systems with On Board Diagnostic (OBD) capability covered here, this Manual should give you the information you need to solve the problem.

We (that is the authors who prepare service literature at the factory) have exactly the same aim as the personnel in the workshops: to make sure that customers are satisfied and to restore their confidence in the product.

The production of a Repair Manual involves a lot of work. Our intention is to describe and explain the technical features and repair measures in such a way that repairs can be completed quickly and correctly. This is not always easy, and good results are only possible if you read the Manual carefully.

Here are some basic points to start with:

• The control module of a system with On Board Diagnostic (OBD) function detects faults and malfunctions during vehicle operation and stores them in a permanent memory, the contents of which remain intact if the power supply from the battery is interrupted.
• The On Board Diagnostic (OBD) function relates to the electrical and electronic parts of a system; in other words it only registers malfunctions which have an effect on the electrical signals.
• The On Board Diagnostic (OBD) function enables malfunctions to be traced quickly and efficiently using VAG 1551 scan tool, or the VAG 1552 vehicle testing system, in operating mode 1 "Rapid data transfer". To do this, the control module of the system concerned must be able to communicate with the scan tool via the diagnostic link-up.
• The diagnostic connector is the interface for communication between the control module and the scan tool.
• To start the troubleshooting procedure, connect the scan tool to the diagnostic connector and establish the communication link with the control module of the system concerned. See VAG 1551 SCAN TOOL, CONNECTING AND ENTERING ADDRESS WORD  .
• When the communication link has been established, you can then select the required troubleshooting functions provided by the on-board system you are testing. These functions are programmed in the form of fixed diagnostic routines, which are described in the relevant sections of this Manual. After first checking the control module version, start with function 02 "Check DTC Memory". See SCAN TOOL FUNCTIONS, SELECTING  .
• Any DTC's which may be stored in the memory will be indicated on the display of the scan tool. The information displayed can then be used in conjunction with a DTC table, which enables you to trace the cause of the malfunction and perform the necessary repair quickly and efficiently.
• The On Board Diagnostic (OBD) function distinguishes between static and sporadic malfunctions. If a malfunction which has been stored in the memory as a static malfunction is no longer present when the ignition is switched on, it is converted into a sporadic malfunction.
• Sporadic malfunctions are identified as such by "/SP" appearing in the display on VAG 1551 scan tool.
• A sporadic malfunction is erased automatically if it no longer occurs over a certain number of driving cycles.
• Static malfunctions remain stored in the DTC memory until the memory is erased with VAG 1551 scan tool.
• If the control module has to be replaced, first read out the control module version. This appears in the display of the scan tool together with the coding when communication is established between the control module and the scan tool. See VAG 1551 SCAN TOOL, CONNECTING AND ENTERING ADDRESS WORD  .