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.

Data bus-compatible control modules 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 malfunction by the engine control module as well as other CAN data bus control modules.

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

Diagnosis via the CAN-bus wire is undertaken via the Data Bus On Board Diagnostic Interface -J533- in the "Gateway".

NOTE: Read out which control modules are actively connected via data bus to the engine control module in measured value blocks 125 and 126.

Further information:
- Self Study Program "The CAN data bus".

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

Special tools and equipment
- V.A.G1598/31 test box
- V.A.G1526 or Fluke 83 multimeter
- V.A.G1594 adapter set
- Wiring diagram

Test sequence
- Switch ignition off.
- Unlock engine control module connector and disconnect.
- Connect V.A.G1598/31 test box to engine control module. Control module wiring harness is not connected by this action.
- Check centralized matching resistor in engine control module.
- To check, measure resistance between test box
Sockets 58 + 60
Specification: 60 to 72 Ohms

If the resistance measurement is outside the specified range:
- Replace engine control module.