1995 AUDI A4 APB Engine Additional Signals Checking Workshop Manual

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Example 1
From the malfunctions present in the DTC memories, you can see that
control module 1 has no connection to control modules 2 or 3.
Electrical Wiring Diagrams, Troubleshooting & Component Locations Control module
Stored malfunctions in DTC memory:
1
No message from control module 2No message from control module 3
2 No message from control module 1
3 No message from control module 1
- Switch ignition off.
- Disconnect control modules that are linked by bus wires and check
whether there is an open circuit in one of the bus wires - If no malfunction can be identified in the bus wires replace control
module 1.
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Example 2
From the malfunctions present in the DTC memories, you can see that
control module 2 has no connection to control modules 1 or 3.
Electrical Wiring Diagrams, Troubleshooting & Component Locations Control module
Stored malfunctions in DTC memory:
1
No message from control module 2
2 No message from control module 1No message from control module 3
3 No message from control module 2
- Switch ignition off.
- Disconnect control modules that are linked by bus wires and check
whether there is an open circuit in one of the bus wires - If no malfunction can be identified in the bus wires replace control
module 2.
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Example 3
From the malfunctions present in the DTC
memories, you can see that none of the control
modules are able to transmit or receive signals.

Control
module
Stored malfunctions in DTC
memory:
1 Data Bus Powertrain
Malfunction
2 Data Bus Powertrain
Malfunction
3 Data Bus Powertrain
Malfunction

- Switch ignition off.

Electrical Wiring Diagrams, Troubleshooting & Component Locations - Disconnect the control modules which are linked by the bus wires and
check for a short circuit between the bus wires
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If the cause of the malfunction "Data Bus Powertrain Malfunction"
cannot be found in the data bus wires, check whether one of the
control modules is causing the malfunction.
At this stage all the control modules which communicate via the CAN data
bus are disconnected. The ignition is switched off. - Check bus wires for short to B+ and short to Ground (GND).
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- Connect one of the control modules.

- Connect VAG1551 scan tool. Switch ignition on
and erase the DTC memory of the control
module which has just been connected. End
output from scan tool with function 06 "End
Output."

- Switch ignition off and then on again.

- Leave ignition switched on for 10 seconds. Then
check DTC memory of the control module that
has just been connected, using the scan tool.

- If the malfunction "Data Bus Powertrain
Malfunction" is now indicated, replace the
control module which has just been connected.

- If malfunction "Data Bus Powertrain Malfunction"
is not indicated, connect next control module,
and repeat above procedure.
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