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) -J623- communicates with other CAN-Bus capable control modules.

The control modules are connected by two data bus wires referred to as CAN High and CAN Low. The CAN bus allows the exchange of information (messages) between the connected modules. Messages that are missing data on the CAN bus are recognized as a malfunction by the control module connected to the CAN bus that received the invalid data.

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 .

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

-- 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 (some models, check Appropriate System Diagrams for correct location) or terminals 18 to 19 (for other models, check Appropriate System Diagrams for correct location) for the specified Terminal Resistance. Refer to Appropriate System Diagrams for terminal locations.

Specified Value: 60 To 72 Ω (At Approx. 20 °C) 

If The Specified Value Was Not Obtained: 

Checking wiring

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

-- 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 T94 for short to ground, high resistance or an open circuit. Refer to Appropriate System Diagrams for terminal locations.

For 2009-2010 Jetta, Golf, Sportwagen and 2012 Passat NMS (Consult Appropriate System Diagrams for specific model) 

Data Bus On Board Diagnostic Interface -J533- electrical harness connector terminals:	Engine Control Module (ECM) -J623- electrical connector T94 terminals:
6 (Can Bus Low)	67
16 (Can Bus High)	68

For 2011> Models: Except 2012 Passat NMS (Consult Appropriate System Diagrams for specific model) 

Data Bus On Board Diagnostic Interface -J533- electrical harness connector terminals:	Engine Control Module (ECM) -J623- electrical connector T94 terminals:
18 (Can Bus Low)	67
19 (Can Bus High)	68

Specified Value: 1.5 Ω Max. 

If The Specified Value Was Not Obtained: 

-- Check the wiring connection for short to ground, high resistance or an open circuit.

-- 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 And The Terminal Resistance Was Not OK: 

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

If No Malfunction Is Found In The Wiring And The Terminal Resistance Was OK: 

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

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 .