CAN-Bus Terminal Resistance, Direct Shift Gearbox (DSG) Mechatronic J743 to Motronic Engine Control Module (ECM) J220 , Checking

Special tools, testers and auxiliary items required 

• Multimeter.
• Wiring diagram.

Test requirement 

• A CAN-Bus malfunction was recognized.
• The Motronic Engine Control Module (ECM) J220 Direct Shift Gearbox (DSG) Mechatronic J743 fuses OK.
• The Direct Shift Gearbox (DSG) Mechatronic 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 (GND) connections between engine/transmission/chassis OK.

• Ignition switched off.

Function 

The Motronic Engine Control Module (ECM) J220 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 Motronic Engine Control Module (ECM) J220 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 Motronic Engine Control Module (ECM) J220.

Test procedure 

• Perform a preliminary check to verify the customers complaint. Refer to → General Diagnosis 

Start diagnosis 

• Disconnect the Direct Shift Gearbox (DSG) Mechatronic J743 electrical harness connector.

• 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:

• 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 Motronic Engine Control Module (ECM) J220.

If the specified value was obtained:

Checking wiring 

If the manufacturers test box is being used. Perform the following step.

• Install the Test Box 105 Pin VAG1598/31. Refer to → 24 MULTIPORT FUEL INJECTION (MFI)

If the manufacturers test box is not being used. Perform the following step.

• Remove the Motronic Engine Control Module (ECM) J220. Refer to → Motronic Engine Control Module (ECM) J220, Replacing .
• Using a Multimeter , check the Direct Shift Gearbox (DSG) Mechatronic J743 electrical harness connector to the Motronic Engine Control Module (ECM) J220 electrical harness connector for resistance.

Direct Shift Gearbox (DSG) Mechatronic J743 electrical harness connector terminals	Motronic Engine Control Module (ECM) J220 electrical connector terminals or test box sockets
15 (Can_Bus Low)	58
10 (Can_Bus High)	60

Specified value: 1.5 Ω 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:

• Erase the DTC memory. Refer to → Diagnostic Mode 04: Reset/Delete Diagnostic Data 
• Perform a road test to verify repair.

If the DTC does not return:

Repair complete, Generate readiness code. Refer to → Readiness Code .

• End diagnosis.

If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:

• Replace the Direct Shift Gearbox (DSG) Mechatronic J743.

Final procedures 

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

1. Check the DTC memory.
2. If necessary, erase the Direct Shift Gearbox (DSG) Mechatronic J743 memory. Refer to Diagnostic Mode 04: Reset/Delete Diagnostic Data .
3. If the DTC memory was erased, generate readiness code. Refer to Readiness Code .

• End of diagnosis.