Terminal Resistance For CAN-Bus, Checking

Terminal Resistance For Can-Bus, Checking

The Engine Control Module (ECM) J623 communicates with all the 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. The central terminal resistor is located in the Engine Control Module (ECM) J623.

Special tools, testers and auxiliary items required
- Multimeter V.A.G 1526 or equivalent.
- Test Box 105 Pin VAG1598/42.
- Adapter Lead Vag1598/39 VAG1598/39.
- Adapter cable V.A.G 1598/39-1.

Test requirement
- Ignition switched off.

Test sequence
- Connect the Test Box 105 Pin VAG1598/42 to the wiring harness of the Engine Control Module (ECM) J623.
- Check the central termination resistor in the Engine Control Module (ECM) J623.
- Using Multimeter V.A.G 1526 A or equivalent, check the following wiring connection between terminal 58 and 60 of the Test box V.A.G. 1598/31 for resistance.
Specified resistance: 60.......72 Ohms

If the specification is exceeded or not met:
- Replace the Engine Control Module (ECM) J623.

If the specified value is obtained:
- Disconnect the Test Box 105 Pin VAG1598/42 from the Engine Control Module (ECM) J623 wiring harness.
- Connect the Test Box 105 Pin VAG1598/42 to the wiring harness of the Engine Control Module (ECM) J623.
- Using Multimeter V.A.G 1526 A or equivalent, check the following wiring connection between terminals 58 and 60 of the Test Box 105 Pin VAG1598/42 for resistance.
Specified resistance 1.5 Ohms max.

If the specification is not obtained:
- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
- If necessary, repair the wiring connection.

Final procedures
After repair work, the following work steps must be performed in the mentioned sequence:
1. Check the DTC memory.
2. If necessary, erase the DTC memory.
3. If the DTC memory was erased, generate readiness code.

- End diagnosis and switch the ignition off.