wiring AUDI A4 1995 B5 / 1.G APB Engine Additional Signals Checking User Guide

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Crash signal, checking

The Engine Control Module (ECM) receives the
crash signal ("Crash shut-down activated") from
the airbag control module.
If the airbag control module sends the crash
signal to the ECM (if an accident occurred or if a
output Diagnostic Test Mode (DTM) was carried
out), the ECM shuts off the fuel pump, that
means the engine stalls, however, afterwards the
engine can be started again (e.g. when removing
the vehicle from the accident area)
The ECM cannot switch off the fuel pump during
an accident if the malfunction "Crash Signal from
Airbag Control Unit/Range Performance" from
the airbag control module is sent to ECM. The
engine control module cannot recognize the
crash signal from the airbag control module; e.g.:
if the wiring between the ECM and the airbag
control module is faulty.

- Connect VAG1598/31 test box to wiring harness
for engine control module. Do not connect to the
engine control module itself Page 24
-20
.
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Test the following wiring connections for open
circuit and/or short to B+ or Ground (GND) and
open circuit.

VAG1598/31 test
box, socket
Airbag control module,
contact
67 Electrical Wiring Diagrams,
Troubleshooting & Component
Locations
Resistance in wiring: max. 1.5 ohm
Eliminate open circuit or short circuit.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations If no malfunctions are found in wiring: Check
DTC memory of airbag control module.
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24-198

Signal for rough road recognition from
ABS/EDL control module, checking


Note:

The ABS/EDL control module generates the
rough road signal if it recognizes wheel spin on
a wheel. The Engine Control Module (ECM)
switches off the misfire recognition once the
rough road signal is recognized by the ECM.
The rough road signal should only be checked if
the malfunction (P1606) 18014 "Rough Road
Spec Engine Torque ABS-ECU/Electrical
Malfunction" is stored in the DTC memory. It is
possible that the malfunction "Misfiring" is also
stored in DTC memory, however this is then a
sequence error and should be ignored.
The wiring and the rough road signal is
monitored by the ECM.
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Test conditions

Control module coding OK Page 01
-93
.

Test sequence

- Connect VAG1598/31 test box to wiring harness
for engine control module. Do not connect to the
engine control module itself Page 24
-20
.

- Check wire from test box socket 74 to ABS
Control Module according to wiring diagram for
short circuit or open circuit.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
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24-206
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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