U2904 – Lost Communication with Vehicle Control Module.

The ODBII code U2904 indicates a loss of communication with the vehicle control module, suggesting that the module is not responding or is unable to communicate with other systems in the vehicle.

The severity of ODBII code U2904 is generally considered moderate to severe.

Common Causes For: U2903 Lost Communication with Vehicle Control Module.

• Faulty Vehicle Control Module (VCM)
• Damaged wiring or connectors
• Poor ground connections
• Corrupted software or firmware
• Faulty communication network (CAN bus issues)
• Low battery voltage
• Intermittent electrical connections
• Malfunctioning sensors or actuators

Common misdiagnosis for U2904 Lost Communication with Vehicle Control Module.

• Faulty Vehicle Control Module (VCM)
• Wiring issues or shorts in the communication lines
• Faulty connectors or terminals
• Issues with other control modules (e.g., Engine Control Module, Transmission Control Module)
• Battery or power supply problems
• Corrupted software or firmware in the control modules
• Faulty sensors related to vehicle communication
• Grounding issues in the electrical system

Common Troubleshooting Steps

The OBD-II code U2904 indicates a “Lost Communication with Vehicle Control Module.” This code typically suggests that there is a communication issue between the vehicle’s control modules, which can be caused by various factors. Here are some common troubleshooting steps to help diagnose and resolve the issue:

• Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes. Sometimes, other codes can provide more context about the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors related to the vehicle control module (VCM) for any signs of damage, corrosion, or loose connections.
• Pay special attention to the wiring harnesses that connect to the VCM and other related modules.
• Check Power and Ground:
• Ensure that the VCM is receiving proper power and ground. Use a multimeter to check the voltage at the module’s power supply pins.
• Verify that the ground connections are secure and free of corrosion.
• Test the Control Module:
• If possible, test the VCM to ensure it is functioning correctly. This may involve using specialized diagnostic equipment or swapping it with a known good module.
• Inspect the CAN Bus:
• The communication between control modules often occurs over the Controller Area Network (CAN) bus. Check for any issues with the CAN bus wiring, such as shorts, opens, or interference.
• Use a CAN bus scanner to monitor the communication and check for any abnormalities.
• Check for Software Updates:
• Sometimes, communication issues can be resolved with a software update. Check with the vehicle manufacturer for any available updates for the VCM or other related modules.
• Clear Codes and Test Drive:
• After performing the above checks and repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code reappears.
• Consult Technical Service Bulletins (TSBs):
• Look for any TSBs related to the U2904 code for your specific vehicle make and model. Manufacturers may have specific recommendations or known issues that can help in troubleshooting.
• Professional Diagnosis:
• If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with experience in diagnosing communication issues. By following these steps, you should be able to identify and resolve the underlying cause of the U2904 code.