Volkswagen Workshop Service and Repair Manuals

Function

The engine control unit communicates with other data bus-compatible control units.

The control units are connected via a twisted pair of data bus wires ("high" and "low") and exchange information (messages). Information missing from the data bus will be recognised as a fault by both the engine control unit and other data bus control units.

The data bus requires a matching resistor to function fault free. This central matching resistor is located in the engine control unit.

Test conditions

• ● A data bus fault has been recognised by the self-diagnosis.

Special tools, workshop equipment, testers, measuring instruments and auxiliary items required

• ◆ Test box V.A.G 1598/31
• ◆ Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
• ◆ Adapter set V.A.G 1594
• ◆ Current flow diagram

Test sequence

• ‒ Switch off ignition.
• ‒ Unlock the engine control unit connector and pull it off.
• ‒ Connect test box V.A.G 1598/31 to engine control unit. The control unit wiring harness is not connected by this action.
• ‒ Check centralized matching resistor in engine control unit.
• ‒ To do this, perform a resistance measurement between
       test box sockets 20 and 21:
       Specification: 60.0...72.0 ω

If the resistance measurement is outside the specified range:

• ‒ Renew engine control unit .

If the resistance value is within the specified range:

• ‒ Repair the fault:

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