WOMS
U code network High severity

U1644 Lost Communication with Body Control Module (BCM)

The OBD2 code U1644 indicates that there is a communication failure between the vehicle's control module and the Body Control Module (BCM), which may affect various electrical functions and systems

Definition

The OBD2 code U1644 indicates that there is a communication failure between the vehicle's control module and the Body Control Module (BCM), which may affect various electrical functions and systems

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

Common misdiagnoses

  • Faulty Body Control Module (BCM)
  • Wiring issues or shorts in the communication lines
  • Faulty Instrument Cluster
  • Defective Powertrain Control Module (PCM)
  • Issues with the CAN bus system
  • Battery or charging system problems
  • Grounding issues
  • Faulty sensors or actuators connected to 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 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 damaged

  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 at the BCM connector

  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, such as cracks or burn marks

  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 Environmental Factors

    Consider if there are any environmental factors (moisture, extreme temperatures) that could be affecting the BCM or its connections

  12. 12. Perform a Hard Reset

    Disconnect the battery for a few minutes to reset the vehicle’s electronic systems. Reconnect and see if the code reappears

  13. 13. Consult Technical Service Bulletins (TSBs)

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

  14. 14. Replace the BCM (if necessary)

    If all other troubleshooting steps fail and the BCM is determined to be faulty, consider replacing it. Ensure proper programming and configuration after replacement.1

  15. 15. Seek Professional Help

    If you are unable to resolve the issue, it may be best to consult a professional mechanic or dealership with experience in diagnosing and repairing BCM-related issues. By following these steps, you should be able to identify the cause of the U1644 code and take appropriate action to resolve the communication issue with the Body Control Module