Testing data exchange between engine control unit, ABS control unit and gearbox control unit — AUDI

APZ ARJ ARN
Special tools and workshop equipment required

V.A.G 1526 A
V.A.G 1594 A
V.A.G 1598/31
VAS 5051 with VAS 5051/1

or

V.A.G 1551 with V.A.G 1551/3 A

Notes:

The data exchange between the various control units is carried out via a data bus.
The term "bus" refers to a system for transmitting and distributing data.
The wires which connect the control units and convey the data between them are called data wires.
The data is transmitted to the various control units in series (i.e. to each control unit in turn) via the data wires.

Testing bus system

If the fault table indicates that the data exchange between the engine control unit, ABS control unit and gearbox control unit should be tested:

Interrogate fault memory of gearbox control unit.

=> Automatic gearbox, Self-diagnosis; Repair group 01; Performing self-diagnosis
Automatic gearbox, Self-diagnosis
Performing self-diagnosis

Interrogate fault memory of ABS control unit.

=> Running gear, Self-diagnosis; Repair group 01; Self-diagnosis, Electrical test
Running gear, Self-diagnosis
Self-diagnosis, Electrical test

If faults have been stored relating to the "data bus" or to "communication":

Check to make sure that the vehicle is fitted with the correct engine control unit, gearbox control unit and ABS control unit. If the correct versions are installed:
Switch off ignition.
Connect test box V.A.G 1598/31 to wiring harness for engine control unit. Do not connect to the engine control unit itself.
=> Page
24-20
.
Using the current flow diagram, test for open circuit and short circuit in the data wires from pins 60 and 58 at the engine control unit to the gearbox control unit (if fitted) and to the ABS control unit. (The data wires to the control unit for continuously-variable transmission are connected to pins 79 and 77 at the engine control unit; see "Important note" below.)

=> Current flow diagrams, Electrical fault finding and Fitting locations

Important note:

The data wires going to the control unit for continuously-variable transmission (if fitted) are connected to pins 79 and 77 at the engine control unit. For all other systems using the data bus, measure at contacts 60 and 58 at the engine control unit.

If the wiring is OK, try renewing first the engine control unit, then the gearbox control unit and/or the ABS control unit.