TCM To ECM Can Bus Terminal Resistance, Checking

Observe all safety precautions: SAFETY PRECAUTIONS 

View clean working conditions: CLEAN WORKING CONDITIONS 

Prior to repair work, perform a preliminary check to verify the condition. Refer to PRELIMINARY CHECK .

Use only gold-plated terminals when servicing any component with gold-plated electrical harness connector terminals.

For wiring diagrams, component locations, and connector views, Refer to the applicable wiring diagram.

Special tools and workshop equipment 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) -J743- 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 connections between Engine / Transmission / Chassis OK.
• Ignition switched off

Function 

The Engine Control Module (ECM) -J623- communicates with the Transmission Control Module (TCM) -J743-.

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. Refer to PRELIMINARY CHECK .

Start diagnosis 

-- Remove the transmission control module. Refer to the appropriate service information for removal and installation procedures.

-- Disconnect the transmission control module electrical harness connector.

-- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

-- Repair as necessary.

-- Using a Multimeter, check the Direct Shift Gearbox (DSG) Mechatronic -J743- electrical harness connector terminals 10 to 15 for resistance.

Specified value: 60 to 72 Ω (at approx. 20 °C)

If the specified value was Not obtained:

Checking wiring 

-- Remove the engine control module. Refer to the appropriate service information for removal and installation procedures.

-- Using a Multimeter, check each of the CAN bus circuits between the transmission control module and the engine control module. Refer to the applicable wiring diagram.

-- Check each CAN circuit for a short to ground, short to voltage, open circuit or high resistance.

-- Repair as necessary.

If the specified value was Not obtained and no malfunction is found in the wiring:

-- Replace the Engine Control Module (ECM) - J623-. Refer to the appropriate service information.

-- Go to Final procedures

If the specified value was obtained:

-- Remove the engine control module. Refer to the appropriate service information for removal and installation procedures.

-- Check each CAN circuit for a short to ground, short to voltage, open circuit or high resistance.

-- Repair as necessary.

If no malfunction is found in the wiring:

-- Replace the transmission control module. DSG transmission Mechatronic - J743- Refer to the appropriate service information for removal and installation procedures.

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 .
2. If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
3. If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .