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U code network Medium severity

U1703 CAN Communication Bus - Missing Message

The OBD2 code U1703 indicates a communication issue in the CAN bus system, specifically that a required message is missing from the network

Definition

The OBD2 code U1703 indicates a communication issue in the CAN bus system, specifically that a required message is missing from the network

Common causes

  • Faulty CAN bus wiring or connectors
  • Malfunctioning CAN bus module
  • Short circuit or open circuit in the CAN bus
  • Faulty or damaged sensors or actuators on the CAN bus
  • Software or firmware issues in the control modules
  • Interference from aftermarket devices
  • Low battery voltage or poor ground connections
  • Corroded or loose connections in the CAN network

Common misdiagnoses

  • Faulty Engine Control Module (ECM)
  • Defective Transmission Control Module (TCM)
  • Bad wiring or connectors
  • Faulty Body Control Module (BCM)
  • Malfunctioning sensors
  • Battery or charging system issues
  • Incorrectly programmed modules
  • Faulty CAN bus transceiver

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 pinpoint the issue

  2. 2. Inspect the Wiring and Connectors

    Visually inspect the wiring and connectors associated with the CAN bus. Look for signs of damage, corrosion, or loose connections

  3. 3. Pay special attention to the connectors at the ECM (Engine Control Module) and other modules on the CAN bus

  4. 4. Test the CAN Bus Voltage

    Use a multimeter to measure the voltage on the CAN High and CAN Low wires. The typical voltage levels should be around 2.5V when idle and should vary when data is being transmitted

  5. 5. If the voltage levels are outside the expected range, there may be a fault in the wiring or a module

  6. 6. Check for Short Circuits or Open Circuits

    Use a multimeter to check for continuity in the CAN bus wiring. Look for any short circuits to ground or open circuits that could disrupt communication

  7. 7. Inspect Modules on the CAN Bus

    Identify all modules connected to the CAN bus and check for any that may be malfunctioning. A faulty module can disrupt communication

  8. 8. Disconnect each module one at a time and check if the code clears or if communication is restored

  9. 9. Check for Interference

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

  10. 10. Update or Reprogram Modules

    Sometimes, a software update or reprogramming of the affected modules may resolve communication issues. Check with the manufacturer for any available updates

  11. 11. Perform a Network Test

    If available, use a professional scan tool to perform a network test. This can help identify which module is not communicating properly

  12. 12. Inspect Ground Connections

    Ensure that all ground connections related to the CAN bus are secure and free of corrosion. Poor grounding can lead to communication issues

  13. 13. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the U1703 code for your specific vehicle make and model. Manufacturers may have specific fixes or recommendations.1

  14. 14. Replace Faulty Components

    If a specific module is identified as faulty, replace it. If wiring issues are found, repair or replace the damaged sections.1

  15. 15. Clear Codes and Test Drive

    After performing repairs, clear the trouble codes and take the vehicle for a test drive to see if the code returns.Conclusion If the issue persists after following these steps, it may be necessary to consult a professional mechanic or technician with experience in automotive electronics and CAN bus systems. They may have access to specialized diagnostic tools and resources to further diagnose the problem