Terminal Resistance For CAN-Bus, Checking

Terminal Resistance For CAN-Bus, Checking

The Engine Control Module (ECM) communicates with all databus-capable control modules via a CAN databus.

These databus-capable control modules are connected via two data bus wires which are twisted together (CAN_High and CAN_Low), and exchange information (messages). Missing information on the databus is recognized as a malfunction and stored.

Trouble-free operation of the CAN-bus requires that it have a terminal resistance. This central terminal resistor is located in the Engine Control Module (ECM).







Recommended special tools and equipment
- V.A.G 1526A multimeter
- V.A.G 1594A connector test kit
- V.A.G 1598/31 test box

Test requirement:
- Ignition switched off.

Test sequence
- Connect test box to the Engine Control Module (ECM); wiring harness is not connected. Test Box, Connecting For Wiring and Component Test
- Check the central termination resistor in the Engine Control Module (ECM):
- Connect multimeter between terminal 58 and 60 of test box for resistance measurement.
- Specified value: 60 to 72 Ohms

If specification is exceeded or not met:
- Replace Engine Control Module (ECM).

If specified value is obtained:
- Disconnect test box from Engine Control Module (ECM).
- Connect test box to control module wiring harness.
- Check CAN data bus wires for shorts among one another.
- Connect multimeter between terminal 58 and 60 of test box for resistance measurement.
- Specified value: Infinite Ohms (no continuity)
- If necessary, repair wire connection according to wiring diagram.