Audi A8 1994 Service Manual page 95

Motronic injection and ignition system (6-cylinder) - Edition 02.1999
When a control unit answers with its identification the number of stored faults appears on the display or "No
fault recognised".
Any system faults that are stored will be displayed one after the other and printed out. The V.A.G 1551 will then
transmit the next address word.
-> The automatic test sequence has ended when the following appears on the display:
V.A.G - SELF-DIAGNOSIS
1 - Rapid data transfer*
2 - Flash code output*
If faults have been stored relating to the "Data bus drive" or to data transmission: "No message from ...."
- Check to make sure that the vehicle is fitted with the correct engine control unit, gearbox control unit, ABS
control unit and dash panel insert (check Part Nos. and coding).
If the correct control units are installed, test the CAN data bus system.
Testing a "two-wire bus system"
Three or more control units communicating via a "two-wire bus system"
- Read out the faults stored in the control units.
This will help to trace a fault in the wiring.
Example 1:
From the faults present in the fault memories, you can see that control unit 1 has no connection to control units
2 or 3.
Control unit Faults present in fault memory:
Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
1 - No message from control unit 2 permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
- No message from control unit 3
2 - No message from control unit 1
3 - No message from control unit 1
- Switch off ignition.
- Disconnect the control units which are linked by the bus wires and check whether there is an open circuit
in one of the bus wires
=> Current flow diagrams, Electrical fault finding and Fitting locations binder
- If no fault can be found in the bus wires replace control unit 1.
HELP
Audi A8 1994 ➤
8.4 - Testing data exchange between control units
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