AUDI A4 1996 B5 / 1.G APB Engine Additional Signals Checking Owner's Guide

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- Press button 0- twice to select "Automatic test
sequence", address word 00. Press -Q- button
to confirm input.


DTC memory of all OBD capable systems in
the vehicle will be checked.
When a control module responds with its
identification, the display indicates the number of
stored errors or indicates "no malfunctions
recognized".
DTCs stored in the system are indicated in
sequence and printed out. Then the VAG1551
scan tool sends the next address word.
VAG - On Board Dia
gnostic
(OBD
) HELP
1- Rapid data transfer*2- Blink code output*

The automatic test sequence is over when the following indication
appears on the display:
If a malfunction related to the"powertrain databus" or the "CAN-bus" is
indicated:
- Check whether the Engine Control Module (ECM) and other CAN
capable control modules installed are appropriate for this vehicle (part
no. and coding).
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If the correct control modules are installed:

- Check to be sure the multi-pin connectors of the
control modules are securely connected.
If multi-pin connectors are properly secured:

- Check CAN-bus system as described in repair
manual Page 24
-202
.

The following trouble shooting procedure is
recommended if three or more control
modules communicate via a "two-wire bus
system".

- Read out malfunctions stored in the control
modules.

This will help to identify a malfunction in the
wiring.
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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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