U2903 – Lost Communication with Vehicle Control Module.

The ODBII code U2903 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 U2903 is generally considered moderate to severe.

Common Causes For: U2902 U2902: “Control Module Communication Failure”

• 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
• Other module failures affecting communication

Common misdiagnosis for U2903 Lost Communication with Vehicle Control Module.

• Faulty Vehicle Control Module (VCM)
• Wiring issues or damaged connectors
• Faulty CAN bus communication
• Power supply issues to the VCM
• Faulty sensors or actuators
• Software or firmware issues
• Battery or ground connection problems
• Other communication-related codes misinterpretation

Common Troubleshooting Steps

The OBD-II code U2903 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 specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to communication problems.
• Seek Professional Help:
• If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or technician who has experience with the specific vehicle and its control systems. By following these troubleshooting steps, you can systematically identify and resolve the underlying cause of the U2903 code.