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U code network High severity

U1079 Communication Bus Off

The OBD2 code U1079 indicates a communication issue where the vehicle's control module is unable to communicate with other modules on the communication bus, often due to a fault in the network or a module failure

Definition

The OBD2 code U1079 indicates a communication issue where the vehicle's control module is unable to communicate with other modules on the communication bus, often due to a fault in the network or a module failure

Common causes

  • Faulty or damaged wiring in the communication bus
  • Failed or malfunctioning control modules
  • Poor connections or corroded terminals in the wiring harness
  • Short circuits in the communication lines
  • Open circuits in the communication lines
  • Interference from aftermarket devices or modifications
  • Low battery voltage or power supply issues
  • Software or firmware issues in the control modules

Common misdiagnoses

  • Faulty ABS module
  • Defective engine control module (ECM)
  • Bad wiring or connectors
  • Malfunctioning body control module (BCM)
  • Issues with the transmission control module (TCM)
  • Faulty sensors
  • Battery or charging system problems
  • Incorrectly diagnosed electrical issues

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

  3. 3. Pay special attention to the connectors for the modules involved in the communication

  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 levels should be around 2.5V to 2.7V when the bus is idle

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

  6. 6. Check for Module Functionality

    Identify the modules that are part of the communication network (e.g., Engine Control Module, Transmission Control Module, Body Control Module)

  7. 7. Test each module for proper operation. If a module is malfunctioning, it may cause communication issues

  8. 8. Inspect for Ground Issues

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

  9. 9. Look for Interference

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

  10. 10. Perform a Network Test

    If available, use a scan tool that can perform a network test to check the status of the communication bus and identify any faults

  11. 11. Clear Codes and Test Drive

    After performing the 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 manufacturer-specific TSBs related to the U1079 code or communication issues. There may be known fixes or updates available

  13. 13. Seek Professional Help

    If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or technician who has experience with automotive electronics and communication systems. By following these troubleshooting steps, you should be able to identify and resolve the underlying issue causing the U1079 code