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U code network High severity

U1389 Control Module Communication Bus Off

The OBD2 code U1389 indicates a communication issue where a control module is unable to communicate on the vehicle's communication bus, often due to a fault in the module or wiring

Definition

The OBD2 code U1389 indicates a communication issue where a control module is unable to communicate on the vehicle's communication bus, often due to a fault in the module or wiring

Common causes

  • Faulty control module
  • Poor electrical connections
  • Damaged wiring or connectors
  • Faulty communication bus (CAN bus) components
  • Software issues or programming errors
  • Low battery voltage
  • Interference from aftermarket devices
  • Corroded terminals or connectors

Common misdiagnoses

  • Faulty control module
  • Wiring issues
  • Poor ground connections
  • Corrupted software/firmware
  • Faulty sensors
  • Battery or power supply issues
  • Communication network problems
  • Intermittent connection issues

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 about the issue

  2. 2. Inspect Wiring and Connectors

    Visually inspect the wiring and connectors related to the control modules. Look for signs of damage, corrosion, or loose connections

  3. 3. Pay special attention to the ground connections, as poor grounding can lead to communication issues

  4. 4. Check the Control Modules

    Identify the control module(s) that may be affected. This could include the engine control module (ECM), transmission control module (TCM), or other modules depending on the vehicle

  5. 5. If possible, test the affected module(s) for proper operation. This may involve using a scan tool to check for communication with the module

  6. 6. Test the Communication Bus

    Use a multimeter or an oscilloscope to check the voltage levels and signal integrity on the communication bus (CAN bus, LIN bus, etc.)

  7. 7. Look for short circuits, open circuits, or abnormal voltage levels that could indicate a problem

  8. 8. Check for Interference

    Ensure that there are no aftermarket devices or modifications that could be interfering with the communication bus

  9. 9. Disconnect any non-factory accessories and see if the code persists

  10. 10. Perform a Hard Reset

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

  11. 11. Update or Reprogram Modules

    If the control module is not responding, it may need to be reprogrammed or updated with the latest software from the manufacturer

  12. 12. Replace Faulty Components

    If a specific module is determined to be faulty after testing, it may need to be replaced

  13. 13. If wiring issues are found, repair or replace the damaged wiring or connectors

  14. 14. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the U1389 code for your specific vehicle make and model. Manufacturers may have known fixes or recommendations

  15. 15. Seek Professional Help

    If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with experience in diagnosing communication issues. By following these steps, you should be able to identify and resolve the underlying issue causing the U1389 code