Can-Bus Terminal Resistance, TCM To ECM, Checking

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 

-- Raise the vehicle to gain access to the Transmission Control Module (TCM) -J743- electrical harness connector.

-- Disconnect the Transmission Control Module (TCM) -J743- electrical harness connector.

-- Using a multimeter, check the Transmission Control Module (TCM) -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.

-- 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 Engine Control Module (ECM) -J623-.

If the specified value was obtained:

Checking wiring 

-- Remove the Engine Control Module (ECM) -J623-.

-- Using a multimeter, check the Transmission Control Module (TCM) -J743- electrical harness connector to the Engine Control Module (ECM) -J623- electrical harness connector T94 for resistance.

Transmission Control Module (TCM) -J743- electrical harness connector terminals	Engine Control Module (ECM) -J623- electrical connector T94 terminals
15 (Can-Bus Low)	67
10 (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.

-- 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 Selector Lever -E313-.

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 .