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
- VAG1526A multimeter
- VAG1594A connector test kit
- VAG1598/31 test box

Test requirement:
- Ignition switched off.

Test sequence
- Connect test box to Engine Control Module (ECM); wiring harness is not connected.
- Check 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: Infinity ohm (no continuity)

- If necessary, repair wire connection according to wiring diagram.

Final procedures
After repair work, the following work steps must be performed in the mentioned sequence:
1. Check DTC memory. Diagnostic Mode 03 - Read DTC Memory
2. If necessary, erase DTC memory. Diagnostic Mode 04 - Erase DTC Memory
3. If DTC memory was erased, generate readiness code.

- End diagnosis and switch ignition off.