With Manufacturer's Scan Tool

CAN-Bus, Checking

Function
The Engine Control Module (ECM) communicates with the ABS/ESP control module, instrument cluster, steering angle sensor and Transmission Control Module (TCM) via a CAN-bus.

At least two data-bus capable control modules are connected and exchange information (messages) via two data-bus wires (CAN_High and CAN_Low) that are twisted to each other. Missing information on the data-bus is recognized as a malfunction by the Engine Control Module (ECM) as well as by other CAN- bus control modules.

The CAN bus requires a matching resistor of 120.0 Ohms to function properly. This matching resistor is located in the engine control module.

Special tools, test equipment and auxiliary items
- Test box V.A.G 1598/31
- Multimeter (Fluke 83 or equivalent)
- Adapter set V.A.G 1594
- Wiring diagram

Check conditions
- A malfunction has been recognized by the CAN bus On Board Diagnostic (OBD)
- ABS control module coded to CAN-bus operation

Test sequence
- Remove inner plenum chamber cover, left:
- Unlock the engine control module connector and pull it off.
- Connect test box V.A.G 1598/31 to engine control module. The control module wiring harness is not connected by this action.
- Check centralized matching resistor in engine control module.
- For this, perform a resistance measurement between test box sockets:
- Sockets 58 + 60 and
- Sockets 77 + 79:
Specification: 115 - 135 Ohms

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

If the resistance value is within the specified range:
- Disconnect test box VAG 1598/31 from engine control module.






- Connect test box VAG 1598/31 to control module wiring harness. Engine control module is not connected by this action
- Check CAN bus wiring for short to one another
- Remove the air cleaner.






- Disengage connector (arrow -1-) and disconnect it from ABS control module (arrow -2-).
- For this, perform a resistance measurement between test box socket 58 + 60:
Specification: Infinity Ohms

Vehicles with automatic gearbox
- Remove inner plenum chamber cover, right:






- Disengage connector (arrow) and disconnect from Transmission Control Module.
- For this, perform a resistance measurement between test box sockets 77 + 79:
Specification: Infinity Ohms

Continued for all vehicles

If the specification is not obtained (wires have short to one another):
- Repair the malfunction in the wiring using wiring diagram:
- Check DTC memory, if necessary, repair any malfunctions and then erase DTC memory, checking and erasing DTC memory. Refer to "Displaying, Reading and Erasing Trouble Codes/With Manufacturers Scan Tool/DTC Memory, Checking And Erasing", Testing and Inspection
- Read-out the readiness code. If the DTC memory has been erased or the engine control module was disconnected from permanent positive, the readiness code must be generated again.
Refer to "Monitors Trips and/or Drive Cycle/Displaying Readiness Code", Testing and Inspection
Refer to "Monitors Trips and/or Drive Cycle/Generating Readiness Code", Testing and Inspection

If the specification is obtained (wires do not have a short to one another):
- Check wiring to CAN bus components for short to battery positive or Ground or open circuit using Wiring diagram:
- Check DTC memory, if necessary, repair any malfunctions and then erase DTC memory, checking and erasing DTC memory. Refer to "Displaying, Reading and Erasing Trouble Codes/With Manufacturers Scan Tool/DTC Memory, Checking And Erasing", Testing and Inspection
- Read-out the readiness code. If the DTC memory has been erased or the engine control module was disconnected from permanent positive, the readiness code must be generated again.
Refer to "Monitors Trips and/or Drive Cycle/Displaying Readiness Code", Testing and Inspection
Refer to "Monitors Trips and/or Drive Cycle/Generating Readiness Code", Testing and Inspection