Can-Bus Terminal Resistance, Checking: Notes

The following procedure is used to diagnose the CAN-Bus terminal resistance of the Engine Control Module - J623- and the Engine Control Module 2 -J624-.

Observe all safety precautions: SAFETY PRECAUTIONS .

View clean working conditions: CLEAN WORKING CONDITIONS .

Prior to repair work, perform a preliminary check to verify the condition. Refer to PRELIMINARY CHECK .

Special tools and workshop equipment required 

• Multimeter.
• Wiring diagram.

Test requirement

• A CAN-Bus malfunction was recognized.
• Engine Control Modules -- 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 (GND) connections between engine/transmission/chassis OK.
• Ignition switched off.

Start diagnosis

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

Function

The Engine Control Module -J623- communicates with the Engine Control Module 2 -J624- and 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-.

Checking internal resistance, Engine Control Module -J623-

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

-- Disconnect theEngine Control Module 2 -J624- electrical harness connector.

-- Using a Multimeter, check the Data Bus On Board Diagnostic Interface -J533- harness connector terminals T32f/5 T32f/21 for resistance.

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

If the specified value was not obtained:

-- Check the wiring. Refer to Checking wiring .

Checking internal resistance, Engine Control Module 2 -J624-

-- Disconnect theData Bus On Board Diagnostic Interface -J533- harness connector.

-- Disconnect theEngine Control Module -J623- harness connector.

-- Using a Multimeter, check the Data Bus On Board Diagnostic Interface -J533- harness connector terminals T32f/5 T32f/21 for resistance.

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

If the specified value was not obtained:

-- Check the wiring. Refer to Checking wiring .