Terminal Resistance For CAN-Bus, Checking

Terminal Resistance For Can-Bus, Checking

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

Special tools, testers and auxiliary items required
- Multimeter.
- Wiring diagram.

Test requirement
- A CAN-Bus malfunction was recognized.
- The Engine Control Module (ECM) J623 fuses OK.
- Battery voltage at least 12.5 V.
- Ignition switched off.

Procedure
- Disconnect the Instrument Cluster Control Module J285 electrical harness connector.

NOTE: The Engine Control Module (ECM) J623 must remain connected for the following step.

- Using a Multimeter, check the Instrument Cluster Control Module J285 electrical harness connector terminals 12 to 13 for resistance.
Specified value: 60 to 72 Ohms (at approx. 20 degrees C)

If the specified value was not obtained:
- Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).
- Check the wiring connection for damage, corrosion, lose or broken terminals.
- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring:
- Replace the Engine Control Module (ECM) J623.

If the specified value was obtained:

If the specified value was obtained:
If the manufacturers test box is being used. Perform the following step.
- Install the test box.

If the manufacturers test box is not being used. Perform the following step.
- Remove the Engine Control Module (ECM) J623.
- Using a Multimeter, check the Instrument Cluster Control Module J285 electrical harness connector to the Engine Control Module (ECM) J623 electrical harness connector T94 for resistance.

Instrument Cluster Control Engine Control Module (ECM) J623
Module J285 electrical harness electrical connector
connector terminals T94 terminals or test box sockets
12 (Can_Bus Low) 67
13 (Can_Bus High) 68

Specified value: 1.5 Ohms Max.

If the specified value was not obtained:
- Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).
- Check the wiring connection for damage, corrosion, lose or broken terminals.
- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring:
- Replace the Instrument Cluster Control Module J285.

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

- End of diagnosis.