Data Bus, Checking

Data Bus, Checking

Function
The engine control module communicates with all control modules capable of data bus via a CAN data bus.

The control modules 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 recognized as a fault by the engine control module as well as other CAN data bus control modules.

Further information:
See Self study programme No. 186 "The CAN data bus".

Test conditions
- A fault has been recognized by the CAN data bus On Board Diagnostic (OBD).

Special tools and equipment
- Test box VAG 1598/31
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram

Test sequence
- Switch off ignition.
- Unlock engine control module connector and pull it off.
- Connect test box VAG 1598/31 to engine control module. Control module wiring harness is not connected by this action.
- Check centralized matching resistor in engine control module.
- To do this perform a resistance measurement between test box sockets
Sockets 58 + 60 and
Sockets 77 + 79
Specification: 60 - 72 ohms

If the resistance measurement is outside the specified range:
- Replace engine electronics control module. Refer to "Engine Control Module (ECM), Replacement" Service and Repair

If the resistance value is within the specified range:
- Repair fault in wiring using wiring diagram: