Checking drive data bus — AUDI

Notes:

If the connector has been detached from a control unit connected to the convenience functions data bus and the ignition is switched on, this may result in a fault entry in the other control units connected to the bus system. The same applies if, for example, the power supply is interrupted by pulling a fuse.
The control unit in the dash panel insert -J285 is the decisive control unit in the drive data bus. The control units in this vehicle that are connected to the drive data bus are entered in it by adaption (depending on the equipment).

=> Electrical System; Repair group 01
Electrical System

The current flow diagrams can be used to establish the number of control units connected to the drive data bus.

=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder

Locating the possible fault cause

Notes:

The following fault locations and fault types are present for the drive data bus:

Drive data bus

Defective:
No data can be transmitted via the bus system
No data can be transmitted on one or both of the bus data wires (CAN-Hi or CAN-Lo)
Read out fault memory:
The control unit in the dash panel insert -J285 cannot transmit a datum due to a fault in a control unit which transmits its data on the drive data bus (Interrogate the fault memory of the control unit in the dash panel insert).
Missing messages (time-out for several control units):
No data were received from one or more control units within the specified time interval.

Control unit in dash panel insert -J285

No communication
No data were received from control unit -J285
Read out fault memory:
Control unit -J285 cannot transmit a datum due to a fault on an upstream component.

Locating fault in drive data bus

Connect fault reader V.A.G 1551 or vehicle diagnostic, testing and information system VAS 5051 to the vehicle's 16-pin diagnostic connector using diagnostic cable VAS 5051/1, with the ignition switched off => Page
01-15
.

Switch the ignition on.
Select function "00 - Interrogating fault memory - Total system"

Display on V.A.S 5051:

All address words stored in the VAS 5051 are now transmitted in succession via the signal wire to the vehicle

Display on V.A.S 5051:

Display zone -1- reads out which address word is currently being transmitted by the VAS 5051.
The control units that have replied are displayed in zone -2-. The number and type of the faults stored in this control unit are also displayed.

Wait until "Function completed" appears in display zone -1-.

Notes:

If a different or additional fault has been stored in a control unit with which the other control units cannot exchange data, this must be rectified before checking the data bus wiring system.
If there is a fault in a control unit, problems may be encountered with the exchange of data with other control units even though this fault does not directly affect the data bus system.
Check the part no. together with the corresponding index of the control unit with which communication is not possible.

=> Parts List

The fault(s) on the drive data bus will only be displayed by the air conditioner operating and display unit -E87:

Check the encoding of the -E87 => Page
01-146
Check signal wires to -E87 for open circuit or line impedance

Wire resistance: max. 1.5 Ohm

=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder

Note:

Pay particular attention to possibility of loose contacts in wiring and connectors.

Fault is located in -E87 if no error can be found.

Fault(s) on the drive data bus is(are) also displayed in another control unit:

Check signal wires and corresponding screening between the various control units connected to the drive data bus for open circuit or line impedance.

Wire resistance: max. 1.5 Ohm

=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder

Check signal wires and corresponding screening between the various control units connected to the drive data bus for mutual short circuit or short to earth/positive.

=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder

=> Electrical System; Repair group 01
Electrical System

Notes:

Pay particular attention to possibility of loose contacts in wiring and connectors.
If this error is not indicated for all control units connected, the problem may be an open circuit at a connection point in the wiring.

If no fault is found, but this fault is displayed for all control units connected to drive data bus, there is a fault in one of the connected control units.

Check the version, the encoding and the entered adaption of the control unit in the dash panel insert -J285.

=> Parts List

=> Electrical System; Repair group 01
Electrical System

Check the version and the encoding of the other control units connected to the drive data bus.

=> Parts List

=> Electrical System; Repair group 01
Electrical System

Unplug all control units except the control unit in the dash panel insert and e.g. the operating and display unit -E87 from the drive data bus.

=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder

Erase the fault memory of the control unit in the dash panel insert and the -E87.

=> Electrical System; Repair group 01
Electrical System

Interrogate the fault memory of the control unit in the dash panel insert and the -E87.

If this fault in the drive data bus is then no longer displayed, the fault is to be found in one of the disconnected control units.

Re-connect the various control units in turn.
Interrogate fault memory following connection of each control unit
Replace the control unit after the installation of which the error is displayed again.

If the fault in the drive data bus continues to be displayed, a fault is present in the control unit in the dash panel insert or in the -E87.

Disconnect the -E87 and connect a different control unit (e.g. the relevant engine control unit).

=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder

Erase the fault memory of the control unit in the dash panel insert and in the engine control unit.

=> Electrical System; Repair group 01
Electrical System

Interrogate fault memory of the control unit in the dash panel insert again.

Note:

Disconnecting the operating and display unit -E87 and connecting a different control unit enables the defective control unit to be located.

Replace the defective control unit