Volkswagen Workshop Service and Repair Manuals

Function

The engine control unit communicates with all control units capable of data bus via a CAN data bus.

The control units capable of data bus are connected together via two data bus wires twisted together (CAN high and CAN low) and exchange information (messages). Information not available in the data bus will be recognised as a fault by the engine control unit as well as other CAN data bus control units.

Further information:

=> Self study programme No. 186 "The CAN data bus".

Test conditions

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

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

• ◆ Test box V.A.G 1598/22
• ◆ 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 1598/22 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 the test box
       Sockets 29 + 41
       Specification: 60 ...72 ω

If the resistance measurement is outside the specified range:

• ‒ Renew engine control unit .

If the resistance value is within the specified range:

• ‒ Rectify wiring fault using current flow diagram:

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