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U code network High severity

U1397 Communication Bus Off

The OBD2 code U1397 indicates a communication issue where the vehicle's communication bus is offline or not functioning properly, affecting data exchange between modules

Definition

The OBD2 code U1397 indicates a communication issue where the vehicle's communication bus is offline or not functioning properly, affecting data exchange between modules

Common causes

  • Faulty wiring or connectors in the communication bus
  • Malfunctioning control modules
  • Short circuits or open circuits in the communication lines
  • Poor ground connections
  • Interference from aftermarket devices
  • Software or firmware issues in the control modules
  • Low battery voltage or power supply issues

Common misdiagnoses

  • Faulty ABS module
  • Defective engine control module (ECM)
  • Malfunctioning transmission control module (TCM)
  • Bad wiring or connectors
  • Faulty body control module (BCM)
  • Incorrectly diagnosed sensor issues
  • Power supply problems
  • Communication issues with other modules

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 communication bus (CAN bus). Look for signs of damage, corrosion, or loose connections

  3. 3. Pay special attention to the connectors at the control modules and any junction points

  4. 4. Test the Communication Bus

    Use a multimeter or an oscilloscope to check the voltage levels on the CAN bus wires. The typical voltage should be around 2.5V to 2.7V when the vehicle is on

  5. 5. Check for short circuits or open circuits in the communication lines

  6. 6. Check Control Modules

    Identify the control modules that are part of the communication network. This may include the engine control module (ECM), transmission control module (TCM), body control module (BCM), etc

  7. 7. If possible, perform a module scan to see if any specific module is not responding

  8. 8. Look for Ground Issues

    Ensure that all ground connections for the control modules are secure and free of corrosion. Poor grounding can lead to communication issues

  9. 9. Inspect for Interference

    Check for any aftermarket devices or modifications that may interfere with the communication bus, such as alarms, remote starters, or stereo systems

  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 returns

  11. 11. Update or Reprogram Modules

    If a specific control module is identified as the issue, check if there are any software updates or reprogramming procedures available 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. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the U1397 code for your specific vehicle make and model. Manufacturers may have known fixes or recommendations.1

  14. 14. Seek Professional Help

    If the issue persists after performing these steps, it may be best to consult a professional mechanic or technician who has experience with your vehicle's specific systems. By following these troubleshooting steps, you should be able to identify and resolve the underlying issue causing the U1397 code