Can-Bus Terminal Resistance, TCM To ECM, Checking

The 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 and workshop equipment required 

• Multimeter.
• Wiring diagram.

Test requirements 

• 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 V.
• Ignition switched off.

Procedure 

-- Disconnect the Transmission Control Module (TCM) -J217- electrical harness connector -direction of the arrow-.

-- Using a Multimeter, check the Transmission Control Module (TCM) -J217- electrical harness connector terminals 2 to 6 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, lose 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 .

If the specified value was obtained:

Checking wiring

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

-- Install the test box. Refer to Wiring and Components, Checking with Test Box VAG 1598/42 .

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 .

-- Using a Multimeter, check the Transmission Control Module (TCM) -J217- electrical harness connector to the Engine Control Module (ECM) -J623- electrical harness connector T94a for resistance.

Transmission Control Module (TCM) -J217- electrical harness connector terminals	Engine Control Module (ECM) -J623- electrical connector T94a terminals or test box sockets
2 (Can_Bus Low)	67
6 (Can_Bus High)	68

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, lose or broken terminals.

-- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring:

-- Replace the Mechatronic unit in the transmission:ATF PAN, ATF FILTER AND MECHATRONIC OVERVIEW .

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 .

-- End of diagnosis.