CAN-Bus Terminal Resistance, TCM to ECM, Checking

CAN-Bus Terminal Resistance, TCM to ECM, Checking

The Motronic 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.

Test procedure

- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check

Start diagnosis

Removal

- Remove the center dash panel - 1 - in the direction of the - arrow -.

- Remove the right upper dashboard panel.





- Remove the three center screws - 1 -





- Remove the right upper dashboard panel - 1 - in the direction of - arrow A - and - arrow B -.





- Remove the retaining screw - arrow -.





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

- Using a Multimeter, check the Transmission Control Module (TCM) (J217) electrical harness connector terminals 85 to 86 for resistance.

Specified value: 60 to 72 ohms (at approx. 20° 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, loose 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). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.

If the specified value was obtained:

Checking wiring

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). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.

- Using a Multimeter, check the Transmission Control Module (TCM) (J217) electrical harness connector to the Engine Control Module (ECM) (J623) electrical harness connector for resistance.





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, loose or broken terminals.

- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring:

- Replace the Transmission Control Module (TCM) (J217). Refer to => [ Transmission Control Module, Replacing ] Service and Repair.

Final procedures

After the repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Mode 03 - Read DTC Memory.

2. If necessary, erase the DTC memory. => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.

3. If the DTC memory was erased, generate readiness code. => [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.