U2104 – Lost Communication with Vehicle Control Module.

The ODBII code U2104 indicates a loss of communication with the vehicle control module, suggesting that the module is not responding or is unable to communicate with other modules in the vehicle’s network.

The severity of ODBII code U2104 is generally considered moderate to severe.

Common Causes For: U2103 Lost Communication with Vehicle Control Module.

• Faulty Vehicle Control Module (VCM)
• Damaged wiring or connectors
• Poor ground connections
• Corrupted software or firmware
• Faulty communication lines (CAN bus issues)
• Malfunctioning other control modules
• Battery or power supply issues
• Intermittent electrical connections

Common misdiagnosis for U2104 Lost Communication with Vehicle Control Module.

• Faulty wiring or connectors
• Defective vehicle control module (VCM)
• Malfunctioning engine control module (ECM)
• Issues with the body control module (BCM)
• Problems with the transmission control module (TCM)
• Faulty sensors or actuators
• Battery or charging system issues
• Corrupted software or firmware in modules
• Grounding issues
• Intermittent communication faults

Common Troubleshooting Steps

The OBD-II code U2104 indicates a “Lost Communication with Vehicle Control Module.” This code typically points to 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. Other codes may provide more context or indicate which module is having communication issues.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors related to the affected control module. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the ground connections, as poor grounding can lead to communication issues.
• Check Power Supply:
• Ensure that the control module has the proper power supply. Use a multimeter to check voltage at the module’s power pins.
• If the module is not receiving power, trace the wiring back to the fuse box and check for blown fuses or damaged wiring.
• Test the Control Module:
• If possible, test the control module itself. This may involve swapping it with a known good module or using a diagnostic tool to check its functionality.
• Some modules may have self-diagnostic capabilities that can provide additional information.
• 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 or opens.
• Use an oscilloscope or a CAN bus diagnostic tool to monitor the bus for proper communication signals.
• 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 control modules.
• Clear Codes and Test Drive:
• After performing any repairs or inspections, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns.
• Consult Technical Service Bulletins (TSBs):
• Look for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued bulletins regarding known issues and recommended fixes.
• Seek Professional Help:
• If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or technician with experience in automotive electronics and diagnostics. By following these troubleshooting steps, you can systematically identify and resolve the underlying cause of the U2104 code.