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U1649 Lost Communication with Body Control Module (BCM)"

The OBD2 code U1649 indicates that there is a communication failure between the vehicle's control module and the Body Control Module (BCM), which may affect various electrical systems and functions

Definition

The OBD2 code U1649 indicates that there is a communication failure between the vehicle's control module and the Body Control Module (BCM), which may affect various electrical systems and functions

Common causes

  • Faulty Body Control Module (BCM)
  • Damaged wiring or connectors
  • Poor ground connections
  • Corroded terminals
  • Faulty communication network (CAN bus issues)
  • Blown fuses
  • Software or firmware issues in the BCM
  • Intermittent electrical connections
  • Other module failures affecting communication

Common misdiagnoses

  • Faulty Body Control Module (BCM)
  • Wiring issues or shorts in the communication lines
  • Faulty or corroded connectors
  • Issues with the power supply to the BCM
  • Malfunctioning other control modules
  • Software or firmware issues in the BCM
  • Problems with the vehicle's battery or charging system
  • Faulty ignition switch or related components

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide more context and help identify related issues

  2. 2. Inspect Wiring and Connectors

    Visual Inspection: Check the wiring harness and connectors leading 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, corroded, or pushed back

  4. 4. Test the BCM

    Power and Ground: Verify that the BCM is receiving proper power and ground. Use a multimeter to check voltage at the BCM connector

  5. 5. Communication Lines

    Check the CAN (Controller Area Network) bus lines for continuity and proper voltage levels

  6. 6. Check for Short Circuits

    Inspect the wiring for any short circuits to ground or to other circuits that could affect communication with the BCM

  7. 7. Inspect Related Modules

    Other modules on the CAN bus may be causing communication issues. Check for codes in other modules and ensure they are functioning properly

  8. 8. Perform a Hard Reset

    Disconnect the vehicle's battery for a few minutes to reset the BCM and other modules. Reconnect and see if the code reappears

  9. 9. Update or Reprogram the BCM

    If the BCM is not functioning correctly, it may need to be reprogrammed or updated with the latest software from the manufacturer

  10. 10. Check for Environmental Factors

    Ensure that there are no environmental factors (like water intrusion) affecting the BCM or its connections

  11. 11. Consult Technical Service Bulletins (TSBs)

    Look for any TSBs related to the specific make and model of the vehicle that may address known issues with the BCM

  12. 12. Replace the BCM (if necessary)

    If all other troubleshooting steps fail and the BCM is determined to be faulty, replacement may be necessary. Ensure that the replacement BCM is compatible with the vehicle.1

  13. 13. Professional Diagnosis

    If you are unable to resolve the issue, consider seeking help from a professional mechanic or dealership with experience in diagnosing BCM-related issues.Conclusion Always remember to take safety precautions when working on a vehicle's electrical system. If you're not comfortable performing these steps, it's best to consult with a professional technician