1995 AUDI A6 ATW Engine Additional Signals Workshop Manual

24-168

Test requirement:

Control module coding OK Page 01
-62
.

Test sequence

- Switch ignition off.

- Connect VAG1598/31 test box at wiring harness
to Engine Control Module (ECM), do not connect
ECM Page 24
-19
.

- Check following wire connection for open circuit
and short circuit to Ground (GND) and B+:

Test box
VAG1598/31
Socket
ABS control module (w/EDL)
-J104-
Terminal
74 Electrical Wiring Diagrams,
Troubleshooting & Component
Locations
If no malfunctions are found in wire:

- Replace ABS control module.
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If the malfunction is indicated again after
replacing the ABS control module:

- Replace Engine Control Module (ECM) Page
24
-23

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24-169

Data transfer between Engine Control
Module (ECM) and CAN-capable control
modules, checking


Note:

Data exchange between individual control
modules occurs via a bus system.
The term "CAN-bus" refers to a system that
transports and distributes data.
The wire connections between the control
modules, via which data is transferred, are
referred to as data wires.
Data is transferred to the connected control
modules serially (one after the other) via these
data wires (i.e. engine speed, accelerator
position).

Checking bus system
The DTC table suggested checking the data
exchange between the Engine Control Module
(ECM) and CAN capable control modules.

-
Connect VAS5051 tester or VAG1551 scan tool
and select control module for engine electronics
using "address word" 01 Page 01
-10
. Ignition
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must remain switched on.
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24-170

Rapid data transfer
HELP
Select function XX

When indicated on display
Note:
Measuring value blocks 125 and 126 indicate the participants in the
powertrain data-BUS. - Press buttons -0- and -8- to select "Read Measuring Value Block" and
press -Q- button to confirm input.
Read measurin
g value block
Q
Enter displa
y group number XXX

When indicated on display
- Press buttons -1-, -2- and -5- to select "display group number 125" and
press -Q- button to confirm input.
Read Measuring Value Block 125
1
2
3
4

When indicated on display
- Check indications in display fields 1 through 4.
CAN capable control modules connected to the Engine Control Module
(ECM) are indicated:

No indication: Control module not CAN-capable
Indication 1: CAN capable control module is connected to databus
Indication 0: CAN capable control module is not connected to
databus
Read Measuring Value Block 126
1
2
3
4

- Check under display group 126 in the same manner.
-
Press button.
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24-171

Rapid data transfer
HELP
Select function XX

When indicated on display
- Press buttons -0- and -6- to select "End output" and press -Q- button to
confirm input.
Rapid data transfer
HELP
Enter address word XX

When indicated on display
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. - 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.
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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24-172
If the correct control modules are installed:

- Check to be sure multi-pin connectors of control
modules are securely connected.
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 DTCs stored in memories of control
modules.

Note:
This analysis will help you locate the cause of the
line malfunction.
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24-173

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 control modules connected across bus wires and check
bus wires for an open circuit. - Replace control module 1 if no malfunctions can be found in bus wires.
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