Can-Bus Terminal Resistance, Transmission Control Module To Engine Control Module, Checking

Special tools and workshop equipment required 

• Multimeter.
• Wiring diagram.

Test requirement 

• A CAN-Bus malfunction was recognized.
• The Engine Control Module (ECM) - J623- Transmission Control Module (TCM) -J217- 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 -J623- 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 Engine Control Module -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 -J623-.

Test procedure 

-- Perform a preliminary check to verify the customers complaint. Refer to PRELIMINARY CHECK 

Start diagnosis 

-- Disconnect the Transmission Control Module -J217- electrical harness connector.

-- Using a multimeter, check the Transmission Control Module -J217- electrical harness connector T 52 terminals 34 to 46 for resistance.

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

If the specified value was obtained: 

-- Check the TCM power and grounds at the module. Refer to the Wiring Diagram. If power or ground is lost, the TCM will not communicate. Correct any power or ground fault before replacement of any component.

If the TCM has power and ground present, Bus resistance was OK but does not communicate: 

-- Replace the Transmission Control Module -J217-.

If the specified Bus resistance was Not obtained: 

-- Remove the Engine Control Module -J623-.

-- Using a multimeter, check the Transmission Control Module -J217- electrical harness connector to the Engine Control Module -J623- electrical harness connector T94 for resistance.

Transmission Control Module -J217- electrical harness connector T52 terminals:	Engine Control Module -J623- electrical connector T94 terminals:
34 (Can-Bus Low)	67 (Can-Bus Low)
46 (Can-Bus High)	68 (Can-Bus High)

Specified value: 1.5 Ω Max.

If the specified resistance 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 -J623-.

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 .

DFD 09/ 2014