Can-Bus Terminal Resistance, 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.
• 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) -- 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 (ECM) -- 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) --.

If the CAN Bus communication is interrupted. Communication from the scan tool to the Engine Control Module (ECM) -- may not be possible.

Test procedure 

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

Start diagnosis

-- Disconnect the Data Bus On Board Diagnostic Interface -J533- electrical harness connector.

-- Using a multimeter, check the Data Bus On Board Diagnostic Interface -J533- electrical harness connector terminals 6 to 16 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, high resistance, 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-. Refer to the Repair Information.

If the specified value was obtained:

Checking wiring 

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

-- Install the test box.

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

-- Remove the Engine Control Module (ECM) -J623-. Refer to the Repair Information.

-- Using a multimeter, check the Data Bus On Board Diagnostic Interface -J533- electrical harness connector to the Engine Control Module (ECM) -J623- electrical harness connector T121 for resistance.

Data Bus On Board Diagnostic Interface -J533- electrical harness connector terminals	Engine Control Module (ECM) -J623- electrical connector T121 terminals or test box sockets
6 (Can Bus Low)	58
16 (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, high resistance, 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 the specified value was obtained:

-- Replace the Data Bus On Board Diagnostic Interface -J533-.

Final procedures 

After 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 .