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U code network High severity

U1981 Lost Communication with the Body Control Module (BCM)

The OBD2 code U1981 indicates that there is a lost communication issue between the vehicle's control module and the Body Control Module (BCM), which may affect various electrical systems and functions

Definition

The OBD2 code U1981 indicates that there is a lost communication issue 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
  • Corroded terminals
  • Blown fuses
  • Faulty communication network (CAN bus issues)
  • Low battery voltage
  • Intermittent electrical connections
  • Software issues or programming errors

Common misdiagnoses

  • Faulty Body Control Module (BCM)
  • Wiring issues or shorts in the communication lines
  • Faulty or corroded connectors
  • Issues with the Powertrain Control Module (PCM)
  • Malfunctioning Instrument Cluster
  • Battery or charging system problems
  • Faulty fuses related to the BCM
  • Software or firmware issues in the BCM
  • Grounding issues in the electrical system
  • Other module communication failures (e.g., ABS, HVAC)

Troubleshooting steps

  1. 1. Check for Other Codes

    Use an OBD-II scanner to check for any additional trouble codes. Sometimes, other codes can provide context or indicate 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 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 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 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: If your vehicle uses a CAN bus system, check the communication lines for continuity and proper voltage levels

  9. 9. Scan Tool

    Use a scan tool to see if you can communicate with the BCM. If you can’t, it may indicate a problem with the BCM itself or the communication lines

  10. 10. Check for Intermittent Issues

    Temperature Sensitivity: Sometimes, issues can be temperature-related. Check if the problem occurs only under certain conditions (e.g., when the vehicle is hot or cold)

  11. 11. Vibration

    Check if the issue occurs when the vehicle is in motion or over bumps

  12. 12. Look for Related Modules

    Other Modules: Check if other modules (like the PCM, ABS, etc.) are communicating properly. A failure in one module can sometimes affect communication with the BCM

  13. 13. 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

  14. 14. 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

  15. 15. 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

  16. 16. 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 U1981 code and take appropriate action to resolve it