TCM Can-Bus Terminal Resistance, Checking

TCM Can-Bus Terminal Resistance, Checking

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.
- The Transmission Control Module (TCM) J217 fuses OK.
- Battery voltage at least 12.5 volts.
- All electrical consumers such as, lights and rear window defroster, switched off.
- Vehicles with automatic transmission, shift selector lever into position "P" or "N".
- A/C switched off.
- Ground (GND) connections between engine/transmission/chassis OK.
- Ignition switched off.

Function
The Engine Control Module (ECM) J623 communicates with other CAN-Bus capable control modules.

The control modules are connected by two data bus wires which are twisted together (CAN_High and CAN_Low), and exchange information (messages). Missing information on the CAN-bus is recognized as a malfunction by the Engine Control Module (ECM) J623 and the other control modules connected to the CAN-bus.

Trouble-free operation of the CAN-Bus requires that it have a terminal resistance. This central terminal resistance is located in the Engine Control Module (ECM) J623.

Test procedure
- Perform a preliminary check to verify the customers complaint. General Diagnosis

Start diagnosis







- Disconnect the electrical connector in the - direction of the arrow - and remove it from the Transmission Control Module (TCM) J217.

NOTE: 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 2 to 6 for resistance.

Specified value: 60 to 72 Ohms (at approx. 20 degree C)

If the specified value was not obtained:
- Using a Multimeter , check the following wiring connections for resistance.

Direct Shift Gearbox (DSG) Engine Control Module (ECM)
Mechatronic J743 electrical J623 electrical connector T94
harness connector terminals terminals or test box sockets
2 (Can_Bus Low) 67
6 (Can_Bus High) 68

Specified value: 1.5 Ohms Max.

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

If no malfunction is found in the wiring and the resistance value was not OK:
- Replace the Engine Control Module (ECM) J623.
- Erase the DTC memory. Diagnostic Mode 04 - Erase DTC Memory
- Perform a road test to verify repair.

If the DTC does not return:
Repair complete, Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
- End of diagnosis.

If the DTC returns and no malfunction is found in the wiring and the resistance value was OK:
- Replace the Transmission Control Module (TCM) J217.

Final procedures
1. Check the DTC memory. Diagnostic Mode 03 - Read DTC Memory
2. If necessary, erase DTC memory of the Transmission Control Module (TCM) J217. Diagnostic Mode 04 - Erase DTC Memory
3. Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

End of diagnosis