2000 AUDI A4 engine

24-201

Data exchange between Engine/ABS/
Transmission control module, checking


Notes:

The data exchange between the various control
modules is carried out via a bus system.
The term "Bus" refers to a system for
transmitting and distributing data.
The wires which connect the control modules
and convey the data between them are called
data wires.
Data is transmitted via data wires in serial, i.e.
in a specific order to the connected control
modules.
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24-202

Checking bus system
The principle of the test is independent of the
number of control modules/systems connected to
the CAN-bus.
The DTC table suggested checking the data
exchange between the Engine Control Module
(ECM) and CAN capable control modules.

- Start engine (if engine will not start, switch
ignition on).

- Connect VAS5051 tester or VAG1551 scan tool
and select the control module for engine
electronics using "address word" 01 Page 01
-
9 .
Rapid data transfer
HELP
Select function XX

When indicated on display:
- 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.
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24-203

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 (display field empty): 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 (e.g. in case of malfunction)
Read measuring value block 125
ABS 1
Combi 1

Example:
Note:
Display group 125 indicates all systems that communicate with the Engine
Control Module (ECM) via the CAN-bus. (In this example, the ABS control
module and the instrument cluster). If these systems are not installed, the
display fields in display group 125 that are intended for them will be
empty. Display field 1 will indicate "Transmission 1" and display field 4 will
indicate "A/C 1" if these systems are communicated with the Engine
Control Module (ECM) via the CAN-bus.
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24-204

Read measuring value block 126
1
2
3
4

Note:
Display group 126 indicates all other systems that communicate with the
Engine Control Module (ECM) via the CAN-bus. If these systems are not
installed, the display fields that are intended for them will be empty.
The following systems will be indicated in display group 126, assuming
they are communicating with the Engine Control Module (ECM) via the
CAN-bus:
Display field 1: automatic distance control; indication: "Distance 1".
Display field 2: Steering angle sensor; indication: "Steering angle 1"
Display field 3: Airbag; indication: "Airbag 1".
Display field 4: System voltage; indication: "cnt. ELEC 1". - Check under display group 126 in the same manner.
-
Press button.
Rapid data transfer
HELP
Enter address word XX

When indicated on display:
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24-205

- 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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