With Manufacturer's Scan Tool

CAN-Bus, checking

1 - Engine Control Module (ECM)
2 - ABS control module
3 - Transmission Control Module (TCM)
- Only vehicles with automatic transmission
4 - Airbag control module
5 - Instrument cluster
6 - CAN-Bus







Function
The Engine Control Module (ECM) (item -1-) communicates with the ABS control module (item - 2-), the Transmission Control Module (item -3-), the airbag control module (item -4-) and the instrument cluster (item -5-) via a CAN-Bus (item -6-).

At least two control modules capable of CAN-Bus are connected by two wires (CAN-High and CAN-Low, twisted together) and exchange information (messages). Missing information on the CAN-Bus will be recognized as a malfunction by the ECM as well as by other CAN-Bus control modules.

All control modules have 120 W terminal resistors which make sure that the CAN-Bus can function without fault.

Special tools and equipment
- Multimeter (Fluke 83 or equivalent)
- VW 1594 adapter set
- Wiring diagram
- VAG1598/21 Test box

Test conditions
- Malfunction has been recognized by CAN-Bus OBD
- ABS control module coded to CAN-Bus operation

Test sequence







- Connect VAG1598/21 test box -1- to ABS control module wiring harness -2-.
- Check terminal resistor in Engine Control Module (ECM) by performing resistance measurement between test box sockets 10 + 11.
- Specified value: 115 to 135 W

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

If the resistance value is within the specified range:
- Check CAN-Bus wiring using wiring diagram.