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Channel 45 (oil grade) 1
1.18 - Checking data exchange between control units
Notes:
◆ Data are exchanged between the individual control units by means of a bus system.
◆ "CAN bus" is the term used to describe a data transfer and distribution system.
◆ The wires between the control units on which data are transmitted are referred to as signal wires.
◆ Data are transmitted serially on these signal wires to the connected control units.
Checking bus system
If fault table indicates that data exchange on bus should be checked.
- Check for proper connection of multi-pin connectors of control units.
Test requirements:
• Vehicle diagnostic, testing and information system VAS 5051 connected up and vehicle self-diagnosis se‐
lected => Page 162
• Ignition on
Sequence of operations
-> Readout on VAS 5051:
- From list -1- select diagnostic function "00 - Interrogate fault memory - entire system".
- Fault memories of all vehicle systems with self-diagnosis capability are interrogated
- Wait until next readout appears.
If a control unit responds with its identification, the number of stored faults or "No faults detected" appears on
the display.
Any stored system faults are consecutively displayed. VAS 5051 then transmits the next address word.
If a fault relating to "Data bus..." or "...no communication" is displayed:
- Check whether correct control units have been fitted for vehicle (part number and code).
If correct control units have been fitted:
- Check for proper connection of multi-pin connectors of control units.
If multi-pin connectors are properly attached:
Audi A8 1994 ➤
Electrical system Self-diagnosis 02.99 ➤ - Edition 05.2002
1.17 - Resetting service display on completion of service work (without VAS 5051) 69
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