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U code network High severity

U1674 Control Module Communication Bus Off

The OBD2 code U1674 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 U1674 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
  • Damaged wiring or connectors
  • Poor ground connections
  • Communication bus interference
  • Faulty or disconnected sensors
  • Software issues or programming errors
  • Low battery voltage or power supply issues
  • Corroded terminals or connectors

Common misdiagnoses

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

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 additional context for the issue

  2. 2. Inspect Wiring and Connectors

    Visually inspect the wiring and connectors related to the control modules on the communication bus. 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 that is reporting the U1674 code. This may require consulting the vehicle's service manual

  5. 5. If possible, test the control module for proper operation. This may involve checking for power and ground at the module and ensuring it is functioning correctly

  6. 6. Test the Communication Bus

    Use a multimeter or an oscilloscope to check the communication signals on the bus. Look for proper voltage levels and signal integrity

  7. 7. If you have access to a scan tool that can monitor live data, check for communication with other modules on the bus

  8. 8. Check for Short Circuits or Open Circuits

    Perform a continuity test on the communication lines to ensure there are no breaks or shorts in the wiring

  9. 9. Check for any shorts to ground or power that could affect communication

  10. 10. Inspect for Interference

    Look for any aftermarket devices or modifications that may interfere with the communication bus. This includes alarms, stereo systems, or other electronic devices

  11. 11. Reset the Codes

    After performing inspections and repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

  12. 12. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the U1674 code for your specific vehicle make and model. Manufacturers may have known issues and recommended fixes

  13. 13. Replace Faulty Components

    If a specific control module is determined to be faulty after testing, it may need to be replaced. Ensure that any replacement module is properly programmed and configured for your vehicle

  14. 14. Seek Professional Help

    If the issue persists after performing these steps, consider seeking help from a professional mechanic or dealership with experience in diagnosing communication issues. By following these troubleshooting steps, you should be able to identify and resolve the underlying issue causing the U1674 code