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U code network High severity

U1521 U1521: Control Module Communication Failure

The OBD2 code U1521 indicates a communication failure between control modules in a vehicle, suggesting that one or more modules are not properly communicating with each other

Definition

The OBD2 code U1521 indicates a communication failure between control modules in a vehicle, suggesting that one or more modules are not properly communicating with each other

Common causes

  • Faulty control module
  • Damaged wiring or connectors
  • Poor ground connections
  • Corrupted software or firmware
  • Communication network issues (CAN bus problems)
  • Intermittent electrical connections
  • Low battery voltage or power supply issues
  • Faulty sensors or actuators affecting communication

Common misdiagnoses

  • Faulty control module
  • Wiring issues or shorts
  • Poor ground connections
  • Corrupted software or firmware
  • Faulty sensors
  • Communication network issues (CAN bus problems)
  • Battery or power supply issues
  • 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. Sometimes, multiple codes can provide more context for the issue

  2. 2. Inspect Wiring and Connectors

    Visual Inspection: Check the wiring and connectors related to the control modules for any signs of damage, corrosion, or loose connections

  3. 3. Repair or Replace

    Repair any damaged wires or connectors and ensure that all connections are secure

  4. 4. Check Power and Ground

    Power Supply: Verify that the control module has the proper power supply. Use a multimeter to check voltage at the module's power pins

  5. 5. Ground Connections

    Ensure that the ground connections are clean and secure. A poor ground can lead to communication issues

  6. 6. Inspect the Control Modules

    Module Functionality: If possible, test the control module in question to ensure it is functioning correctly. This may involve swapping it with a known good module

  7. 7. Software Updates

    Check if there are any software updates available for the control module. Sometimes, manufacturers release updates to fix communication issues

  8. 8. Check for Interference

    Aftermarket Accessories: If any aftermarket accessories have been installed, they may interfere with the communication between modules. Temporarily disconnect them to see if the issue resolves

  9. 9. Signal Interference

    Ensure that there are no sources of electromagnetic interference near the vehicle's wiring

  10. 10. Perform a Network Test

    Use a scan tool capable of performing a network test to check the communication between modules. This can help identify which module is not communicating properly

  11. 11. Clear Codes and Test Drive

    After performing the above checks 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 specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to U1521

  13. 13. Seek Professional Help

    If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or dealership for further diagnosis. They may have specialized tools and knowledge to address complex communication issues. By following these troubleshooting steps, you can systematically identify and resolve the underlying cause of the U1521 code