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U1955 Lost Communication with Body Control Module (BCM)

The OBD2 code U1955 indicates a loss of communication between the vehicle's control module and the Body Control Module (BCM), suggesting a potential issue with wiring, connectors, or the BCM itself

Definition

The OBD2 code U1955 indicates a loss of communication between the vehicle's control module and the Body Control Module (BCM), suggesting a potential issue with wiring, connectors, or the BCM itself

Common causes

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

Common misdiagnoses

  • Faulty Body Control Module (BCM)
  • Wiring issues or damaged connectors
  • Faulty or corroded ground connections
  • Malfunctioning ignition switch
  • Issues with the power supply to the BCM
  • Other communication network failures (e.g., CAN bus issues)
  • Faulty sensors or actuators connected to the BCM
  • Software or firmware issues in the BCM

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 the Wiring and Connectors

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

  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. Test Communication Lines

    CAN Bus: Use a scan tool to check the communication on the CAN bus. If other modules are not communicating, there may be a fault in the bus itself

  9. 9. Scope Testing

    If available, use an oscilloscope to check for proper signal patterns on the communication lines

  10. 10. Check for Short Circuits

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

  11. 11. Look for Intermittent Issues

    If the code is intermittent, try to replicate the conditions under which the code appears. This could involve checking for specific vehicle conditions (e.g., temperature, humidity, etc.)

  12. 12. Reset the Codes

    Clear the trouble codes using the OBD-II scanner and see if the code returns. If it does, further investigation is needed

  13. 13. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the BCM or communication issues for your specific vehicle make and model. Manufacturers may have known fixes for common problems

  14. 14. Professional Diagnosis

    If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership. They may have specialized tools and knowledge to diagnose complex communication issues.Conclusion Troubleshooting a U1955 code can be complex, as it often involves multiple systems and components. Following these steps systematically can help isolate the problem and lead to a resolution. Always ensure safety and proper procedures when working on vehicle electronics