AUDI A4 1999 B5 / 1.G AWM Engine Additional Signals Checking Owner's Manual

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If multi-pin connectors are properly secured:

- Check CAN bus system

Checking a "two-line bus system"

Three or more control modules are
communicating across a "two-line bus
system".

- Analyze the DTCs stored in the memories of the
control modules.

Note:
This analysis will help you locate the cause of the
line malfunction.
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Example 1:
From the DTCs stored in the memories, you have determined that control
module 1 is not communicating with control modules 2 and 3.
Electrical Wiring Diagrams, Troubleshooting & Component Locations Control module
DTCs stored in DTC memories:
1
Missing signal from control module 2Missing signal from control module 3
2 Missing signal from control module 1
3 Missing signal from control module 1
- Switch ignition off.
- Disconnect the control modules connected across the bus wires and
check the bus wires for an open circuit. - Replace control module 1 if no malfunctions can be found in the bus
wires.
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Example 2:
From the DTCs stored in the memories, you have determined that control
module 2 is not communicating with control modules 1 and 3.
Electrical Wiring Diagrams, Troubleshooting & Component Locations Control module
DTCs stored in DTC memories:
1
Missing signal from control module 2
2 Missing signal from control module 1Missing signal from control module 3
3 Missing signal from control module 2
- Switch ignition off.
- Disconnect the control modules connected across the bus wires and
check the bus wires for an open circuit. - Replace control module 2 if no malfunctions can be found in the bus
wires.
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Example 3:
Using the DTCs stored in the memories, you
have determined that none of the control
modules are sending or receiving signals.

Control
module
DTCs stored in DTC
memories:
1
Powertrain CAN-bus faulty
2 Powertrain CAN-bus faulty
3 Powertrain CAN-bus faulty

- Switch ignition off.

Electrical Wiring Diagrams, Troubleshooting & Component Locations - Disconnect the control modules connected across the bus wires and
check bus wires for a short circuit to B+ and Ground (GND).
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If you cannot determine a cause for the DTC
"Powertrain CAN-bus malfunction, check
whether the DTC is caused by one of the
control modules.
All control modules that use the CAN-bus are still
disconnected. Ignition is switched off.

- Connect one of the control modules.

- Connect VAG 1551 scan tool. Switch ignition on,
and erase the DTC memory of the control
module you just connected. End scan tool output
using the "End Output" function 06.

- Switch ignition off and on again.

- Leave ignition on for 10 seconds. Then, read the
DTC memory of the control module you just
connected.

- If the DTC "Powertrain CAN-bus malfunction" is
displayed, replace the control module you just
connected.

- If the DTC "Powertrain CAN-bus malfunction" is
not displayed, connect the next control module
and repeat the procedure.
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