U1921 – Body Control Module Communication Error

The ODBII code U1921 indicates a communication error between the Body Control Module (BCM) and other modules in the vehicle’s network, suggesting a potential issue with wiring, connectors, or the BCM itself.

The severity of ODBII code U1921 is moderate.

Common Causes For: U1920 U1920: “Module Communication Failure”

• Faulty Body Control Module (BCM)
• Damaged wiring or connectors
• Poor ground connections
• Corroded terminals
• Faulty communication network (CAN bus)
• Software issues or bugs in the BCM
• Low battery voltage or power supply issues
• Interference from aftermarket accessories or modifications

Common misdiagnosis for U1921 U1921: Body Control Module Communication Error

• Faulty Body Control Module (BCM)
• Wiring issues or shorts in the communication lines
• Faulty or corroded connectors
• Malfunctioning Engine Control Module (ECM)
• Issues with other control modules (e.g., Transmission Control Module)
• Battery or charging system problems
• Software or firmware issues in the BCM or other modules
• Grounding issues in the electrical system

Common Troubleshooting Steps

When dealing with OBD-II code U1921, which indicates a Body Control Module (BCM) communication error, there are several common troubleshooting steps you can follow to diagnose and potentially resolve the issue. Here’s a structured approach:

• Check for Additional Codes: Use an OBD-II scanner to check for any other trouble codes that may be present. Sometimes, multiple codes can provide more context for the issue.
• Inspect Wiring and Connectors: **Visual Inspection: Check the wiring and connectors related to the BCM for any signs of damage, corrosion, or loose connections.
• **Connector Pins: Ensure that the pins in the connectors are not bent or corroded.
• Check Power and Ground: **Power Supply: Verify that the BCM is receiving the correct voltage. Use a multimeter to check the power supply to the BCM.
• **Ground Connections: Ensure that the ground connections for the BCM are secure and free of corrosion.
• Inspect the BCM: **Physical Condition: Check the BCM for any signs of physical damage or water intrusion.
• **Reprogramming: If the BCM has been replaced, ensure that it has been properly programmed to the vehicle.
• Check Communication Lines: **CAN Bus: If your vehicle uses a Controller Area Network (CAN) bus, check the communication lines for continuity and proper resistance.
• **Network Issues: Look for any other modules on the network that may be causing communication issues. Disconnecting other modules one at a time can help isolate the problem.
• Test the BCM: If possible, test the BCM using a scan tool that can communicate with it. Check for any response or data that the BCM should provide.
• If you have access to a known good BCM, you can swap it temporarily to see if the issue resolves.
• Check for Software Updates: Sometimes, manufacturers release software updates for the BCM. Check with the dealership or manufacturer to see if there are any updates available.
• 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 returns.
• Consult a Professional: If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with your specific vehicle make and model.Additional Tips: – Always refer to the vehicle’s service manual for specific diagnostic procedures and specifications. – Ensure that you have the proper tools and safety equipment when working on the vehicle. By following these steps, you should be able to diagnose and potentially resolve the U1921 code related to the Body Control Module communication error.