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With Manufacturer's Scan Tool



CAN-Bus, Checking

Function
The Engine Control Module (ECM) communicates with the ABS/ESP control module, airbag 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.

Special tools and equipment
- Multimeter (Fluke 83 or equivalent)
- VW1594 adapter set
- Wiring diagram
- VAG1598/21 test box

Test conditions
- Malfunction has been recognized by CAN- Bus On Board Diagnostic (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).
- To do this, perform resistance measurement between test box sockets 10 + 11:
Specified value: 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:
- Check CAN-Bus wiring using wiring diagram.
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