WOMS
U code network Medium severity

U1921 U1921: Body Control Module Communication Error

The OBD2 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

Definition

The OBD2 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

Common causes

  • 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 misdiagnoses

  • 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

Troubleshooting steps

  1. 1. 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

  2. 2. Inspect Wiring and Connectors

    Visual Inspection: Check the wiring and connectors related to the BCM for any signs of damage, corrosion, or loose connections

  3. 3. Connector Pins

    Ensure that the pins in the connectors are not bent or corroded

  4. 4. 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

  5. 5. Ground Connections

    Ensure that the ground connections for the BCM are secure and free of corrosion

  6. 6. Inspect the BCM

    Physical Condition: Check the BCM for any signs of physical damage or water intrusion

  7. 7. Reprogramming

    If the BCM has been replaced, ensure that it has been properly programmed to the vehicle

  8. 8. Check Communication Lines

    CAN Bus: If your vehicle uses a Controller Area Network (CAN) bus, check the communication lines for continuity and proper resistance

  9. 9. 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

  10. 10. 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

  11. 11. If you have access to a known good BCM, you can swap it temporarily to see if the issue resolves

  12. 12. 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

  13. 13. 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

  14. 14. 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