TCM To ECM Can Bus Terminal Resistance, Checking

The Engine Control Module -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 -J623-.

Special tools and workshop equipment required

Multimeter
Wiring Diagram

Test requirements

A CAN malfunction was recognized
Fuses OK.
Battery voltage OK.
Switch OFF all electrical and electronic accessories.
Vehicles with Auto. Transmission, ensure Selector Lever position is in "P".
Vehicles with Man. Transmission, ensure Shifter Lever position is in "N" with Parking Brake applied.
Coolant Temperature: ≥ 80° C.
Observe all safety precautions: SAFETY PRECAUTIONS .
View clean working conditions: CLEAN WORKING CONDITIONS .

Test Procedure

Step	Procedure	Result / Action to Take
1	PERFORM: Preliminary Check to verify the customers complaint. Refer to PRELIMINARY CHECK . -- Was Complaint verified?	YES: GO TO Step 2. NO: GATHER more information from customer about the complaint.
2	Remove the DSG Transmission Mechatronic -J743-. Refer to appropriate repair Information. Disconnect the DSG Transmission Mechatronic -J743- harness connector. Check the harness connector for damage, corrosion, loose, or broken terminals. Repair as necessary. -- Do any DTC's return:	YES: GO TO: Step 3. NO: GO TO: Step 5.
3	The Engine Control Module -J623- must remain connected for the following step. The central terminal resistor is located in the Engine Control Module -J623-. Using a multimeter, check the DSG Transmission Mechatronic -J743- harness connector T20e / 10 to T20e / 15 for resistance. Specified value: 60 to 72 Ω (at approx. 20° C). -- Was Value obtained?	YES: GO TO: Step 4. NO: CHECK: Wiring for open, high resistance, short or harness connector for damage, corrosion, loose or broken terminals. REPAIR: Faulty wiring or connector. GO TO: Step 5.
4	REMOVE: Engine Control Module - J623-. Refer to appropriate repair Information. Using a multimeter, check the CAN bus circuit between T20e / 10 of the DSG Transmission Mechatronic -J743- and T94 / 68 of the Engine Control Module -J623- for resistance. Using a multimeter, check the CAN bus circuit between T20e / 15 of the DSG Transmission Mechatronic -J743- and T94 / 67 of the Engine Control Module -J623- for resistance. SPECIFIED VALUE: 0.5 Ω (± 0.3 Ω). -- Were Values obtained?	YES: Remove the Engine Control Module -J623-. Refer to the appropriate repair Information. Check each CAN circuit for a short to ground, short to voltage, open circuit or high resistance. If no malfunction is found in the wiring: Replace the DSG Transmission Mechatronic -J743-. Refer to the appropriate repair Information. GO TO: Step 5. NO: If the specified resistance value was not obtained and no malfunction is found in the wiring: Replace the Engine Control Module -J623-. Refer to the appropriate repair Information. GO TO: Step 5.
5	Final Procedure Perform a road test to verify repair. Do any DTC's return:	YES: Check the DTC memory. Refer to DIAGNOSTIC MODE 03 - READ DTC MEMORY . Perform the diagnostic procedure for that DTC. NO: Repair is complete. Generate readiness code. Refer to READINESS CODE . Return vehicle to Customer.

DFD 09/2014