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U1117 Control Module Communication Bus Off

The OBD2 code U1117 indicates a communication issue where a control module is not responding or is offline on the communication bus, potentially due to a fault in the module or wiring

Definition

The OBD2 code U1117 indicates a communication issue where a control module is not responding or is offline on the communication bus, potentially due to a fault in the module or wiring

Common causes

  • Faulty control module
  • Damaged wiring or connectors
  • Poor ground connections
  • Communication bus short circuit
  • Open circuit in the communication bus
  • Intermittent electrical connections
  • Faulty or incompatible aftermarket components
  • Software or firmware issues in the control module

Common misdiagnoses

  • Faulty control module
  • Wiring issues
  • Poor ground connections
  • Faulty sensors
  • Battery or charging system problems
  • Corrupted software or firmware
  • Communication network 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. Other codes can provide context and help identify the root cause of the communication issue

  2. 2. Inspect Wiring and Connectors

    Visually inspect the wiring and connectors associated with the control module that is reporting the U1117 code. Look for signs of damage, corrosion, or loose connections

  3. 3. Pay special attention to the CAN bus wiring, which typically consists of a twisted pair of wires

  4. 4. Test the Control Module

    If possible, test the control module that is reporting the U1117 code. This may involve checking for proper power and ground at the module

  5. 5. If the module is removable, consider swapping it with a known good module to see if the problem persists

  6. 6. Check for Short Circuits or Open Circuits

    Use a multimeter to check for short circuits or open circuits in the CAN bus wiring. Ensure that the resistance between the CAN High and CAN Low wires is within specifications

  7. 7. Inspect Other Modules

    Check other control modules on the CAN bus for faults. A malfunctioning module can cause communication issues for the entire bus

  8. 8. Disconnect other modules one at a time to see if the U1117 code clears, indicating that one of the other modules may be causing the issue

  9. 9. Check for Interference

    Look for any aftermarket devices or modifications that may be interfering with the CAN bus communication. This includes things like alarm systems, stereo systems, or other electronic accessories

  10. 10. Update or Reprogram Modules

    In some cases, a software update or reprogramming of the control module may be necessary. Check with the manufacturer for any available updates

  11. 11. Scan Tool Communication

    Ensure that your OBD-II scanner is functioning properly and can communicate with all modules. Sometimes, a faulty scanner can give misleading information

  12. 12. Battery and Ground Connections

    Check the vehicle's battery and ground connections. A weak battery or poor ground can lead to communication issues

  13. 13. Consult Technical Service Bulletins (TSBs)

    Look for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to the U1117 code.1

  14. 14. Professional Diagnosis

    If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership. They may have specialized tools and knowledge to diagnose complex communication issues. By following these steps, you should be able to identify and resolve the underlying issue causing the U1117 code