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U code network Medium severity

U2391 U2391: Vehicle Communication Bus Malfunction

The OBD2 code U2391: Vehicle Communication Bus Malfunction indicates a problem with the communication network between various control modules in the vehicle, which may affect their ability to exchange data properly

Definition

The OBD2 code U2391: Vehicle Communication Bus Malfunction indicates a problem with the communication network between various control modules in the vehicle, which may affect their ability to exchange data properly

Common causes

  • Faulty wiring or connectors in the communication bus
  • Malfunctioning control modules
  • Corrupted software or firmware in the modules
  • Poor ground connections
  • Interference from aftermarket devices
  • Damaged or shorted communication lines
  • Low battery voltage or power supply issues
  • Faulty or incompatible OBD-II scanner or tool

Common misdiagnoses

  • Faulty Engine Control Module (ECM)
  • Defective Body Control Module (BCM)
  • Wiring issues or shorts in the communication bus
  • Bad connectors or terminals
  • Malfunctioning sensors
  • Issues with the powertrain control module (PCM)
  • Problems with the diagnostic connector
  • Software glitches or outdated firmware in modules

Troubleshooting steps

  1. 1. Check for Other Codes

    Use an OBD-II scanner to check for any additional trouble codes. Sometimes, related codes can provide more context for the issue

  2. 2. Inspect the Wiring and Connectors

    Visual Inspection: Look for damaged, frayed, or corroded wiring and connectors related to the communication bus (CAN bus)

  3. 3. Connector Integrity

    Ensure that all connectors are securely attached and free of corrosion

  4. 4. Check the Battery and Ground Connections

    Ensure that the vehicle's battery is in good condition and fully charged

  5. 5. Inspect ground connections for corrosion or looseness, as poor grounding can affect communication

  6. 6. 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 when the bus is idle

  7. 7. Look for any short circuits or open circuits in the communication lines

  8. 8. Inspect Control Modules

    Check if any control modules (ECU, TCM, BCM, etc.) are malfunctioning. A faulty module can disrupt communication

  9. 9. If possible, perform a software update or reset on the control modules

  10. 10. Check for Interference

    Look for any aftermarket devices or modifications that may interfere with the vehicle's communication systems, such as alarms, remote starters, or audio systems

  11. 11. Perform a Network Test

    If available, use a scan tool that can perform a network test to check the communication between modules. This can help identify which module is not communicating properly

  12. 12. Clear Codes and Test Drive

    After performing the above checks and repairs, clear the trouble codes using the OBD-II scanner

  13. 13. Take the vehicle for a test drive to see if the code reappears

  14. 14. Consult Technical Service Bulletins (TSBs)

    Check for any manufacturer-specific TSBs related to U2391 or communication issues for your vehicle make and model

  15. 15. Seek Professional Help

    If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who specializes in automotive electronics. By following these troubleshooting steps, you can systematically identify and resolve the underlying cause of the U2391 code