CAN-Bus Checking

CAN-Bus, Checking

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

The control modules capable of CAN-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 CAN-Bus will be recognized as a fault by the engine control module as well as other CAN-Bus control modules.

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


NOTE: You can read out which control modules are actively connected via CAN-Bus to the engine control module in measured value blocks 125 and 126. Refer to "Scan Tool Testing/Measuring Value Blocks/Evaluating Measured Value Blocks/Display Groups 120 to 129 (Communication)" Testing and Inspection


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

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

Test sequence
- Switch ignition off.
- Remove inner plenum chamber cover left:
- Unlock engine control module connector and disconnect.







- Connect test box V.A.G 1598/31 to engine control module. Control module wiring harness is not connected by this action.
- Check centralized matching resistor in engine control module.
- Perform a resistance measurement between test box sockets:
- Sockets 58 + 60
Specification: 60 - 72 Ohms

If the resistance value is outside the specified range:
- Replace Engine Control Module (ECM).

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