AUDI A8 1998 D2 / 1.G 01V Transmission Torque Tube Remove And Install Workshop Manual

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CAN-bus, function

Bus:
The term "bus" refers to a system that transports
and distributes data.

CAN:
The Controller Area Network is a bus system that
uses two wires. These are called bus wires. Data
is transferred to the connected control modules
serial (one after the other) across the bus wires.
These control modules communicate with each
other via the CAN-bus.

Overview of power train data-BUS
1 - Transmission Control Module (TCM) -J217-
2 - Driver for BUS
3 - Motronic Engine Control Module (ECM) -J220-
4 - Driver for BUS
5 - Termination resistance
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6 - Power train data-BUS (CAN-bus, twisted 2 line wire)
7 - Termination resistance
8 - Driver for BUS
9 - ABS Control Module -J104-
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Two-wire bus system, checking


If the DTC table indicates to check the bus:

- Use the applicable wiring diagram, determine
how many control modules communicate with
each other via the bus.

- Press the -0- button twice to select the function
"Automatic test sequence".

- Before checking the bus wires, make sure that
none of the control modules connected are
malfunctioning.

A malfunction will disrupt communication to
other control modules.

Is there a malfunction?

- Fix the malfunction before proceeding.

- Note malfunction and erase DTC memory of all
control modules Checking and erasing DTC
memory of the relevant control module.
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- Press buttons -0- and -6- to select "End Output"
function 06. Press -Q- button to confirm input.

- End output of scan tool by selecting the function
"end output" page 01
-42
.

- Refer to the DTC table in the applicable repair
manual for help in repairing the malfunction.
When necessary repairs have made:

- Check bus wires if communication to the control
modules is still faulty. If yes, check bus wires.

There can be two situations:

Two control modules communicate via a "two-
line bus system"
Three or more control modules communicate
via a "two-line bus system"
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Two control modules communicate via a
"two-line bus system"

- Switch ignition off.

Electrical Wiring Diagrams, Troubleshooting & Component Locations - Disconnect both control modules.
- Check bus wires for open circuit.

Electrical Wiring Diagrams, Troubleshooting & Component Locations - Check whether there is a short circuit between bus wires.
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If there are no malfunctions in the bus wires: - Check bus wires for short circuit to B+ or Ground (GND).
- As a test, replace one of the control modules. Select a control module
that will take the least amount of time to replace and cost the least
amount of money.
- If communication between the control modules across the bus is still
interrupted, replace the second control module.
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Three or more control modules are
communicating across a "two-line bus
system"

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

Example 1:
From the DTCs stored in the memories, 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 bus wires for open circuit. - Replace control module 1 if bus wires are OK.
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Example 2:
From the DTCs stored in the memories, 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 bus wires for open circuit. - Replace control module 2 if bus wires are OK.
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Example 3:
Using DTCs stored in the memories, determined
that none of the control modules are sending or
receiving signals.

Control
module DTCs stored in DTC
memories:
1
Hardware faulty
2 Hardware faulty
3 Hardware faulty

- Switch ignition off.

Electrical Wiring Diagrams, Troubleshooting & Component Locations - Disconnect the control modules connected across the bus wires and
check for a short circuit between the bus wires.

- Check bus wires for short circuit to B+ or Ground (GND).
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- If there are no malfunctions found in the bus
wires, check whether one of the control modules
is responsible for a short circuit of the bus wires
to each other, to B+ or to Ground (GND).

Disconnect each of the control modules
connected via the bus wires one at a time and
check whether the malfunction "Hardware faulty"
has been eliminated.

If it was eliminated, replace the control module
that is currently disconnected. If malfunction was
not eliminated, re-connect that control module
and disconnect the next control module
connected via the bus wires.
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