WOMS
U code network Medium severity

U021A U021A: "Missing Message from Vehicle Communication Network

The OBD2 code U021A indicates that a communication issue has occurred, specifically that a message expected from a vehicle communication network is missing or not being received by the vehicle's control module

Definition

The OBD2 code U021A indicates that a communication issue has occurred, specifically that a message expected from a vehicle communication network is missing or not being received by the vehicle's control module

Common causes

  • Faulty wiring or connectors
  • Malfunctioning control module
  • Communication network issues (e.g., CAN bus problems)
  • Corrupted software or firmware in modules
  • Poor ground connections
  • Intermittent electrical issues
  • Faulty sensors or actuators
  • Aftermarket modifications or installations affecting communication

Common misdiagnoses

  • Faulty wiring or connectors
  • Defective control modules
  • Software issues or updates needed
  • Battery or power supply problems
  • Intermittent communication issues
  • Incorrectly installed aftermarket accessories
  • Faulty sensors or actuators
  • Grounding issues

Troubleshooting steps

  1. 1. Check for Other Codes

    Start by scanning the vehicle for any additional trouble codes. Sometimes, multiple codes can provide more context for the issue

  2. 2. Inspect Wiring and Connectors

    Examine the wiring and connectors associated with the affected modules. Look for signs of damage, corrosion, or loose connections that could disrupt communication

  3. 3. Verify Module Functionality

    Identify the specific module that is reporting the U021A code. Check if the module is functioning correctly. This may involve testing the module's inputs and outputs

  4. 4. Check for Software Updates

    Ensure that all vehicle modules have the latest software updates. Sometimes, communication issues can be resolved with a software update

  5. 5. Perform a Network Scan

    Use a professional-grade scan tool to perform a network scan. This can help identify which modules are communicating properly and which are not

  6. 6. Inspect the CAN Bus

    If the vehicle uses a Controller Area Network (CAN) bus, check the integrity of the bus. Look for shorts, opens, or other issues that could affect communication

  7. 7. Test Power and Ground

    Ensure that the affected module has proper power and ground connections. Use a multimeter to check voltage and ground continuity

  8. 8. Check for Interference

    Look for any aftermarket devices or modifications that may interfere with the vehicle's communication network

  9. 9. Clear Codes and Test Drive

    After performing any repairs or adjustments, clear the trouble codes and take the vehicle for a test drive to see if the code returns

  10. 10. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common communication issues. 1

  11. 11. Professional Diagnosis

    If the issue persists after performing the above steps, consider seeking help from a professional technician or dealership with experience in diagnosing communication issues. By following these steps, you can systematically identify and address the underlying cause of the U021A code