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U1704 CAN Communication Bus Fault

The OBD2 code U1704 indicates a fault in the CAN (Controller Area Network) communication bus, suggesting a problem with data transmission between modules in the vehicle's network

Definition

The OBD2 code U1704 indicates a fault in the CAN (Controller Area Network) communication bus, suggesting a problem with data transmission between modules in the vehicle's network

Common causes

  • Faulty CAN bus wiring or connectors
  • Defective CAN bus module
  • Short circuit in the CAN bus
  • Open circuit in the CAN bus
  • Interference from other electrical components
  • Faulty or incompatible aftermarket accessories
  • Software or firmware issues in the control modules
  • Low battery voltage or poor ground connections

Common misdiagnoses

  • Faulty Engine Control Module (ECM)
  • Defective Transmission Control Module (TCM)
  • Bad wiring or connectors
  • Faulty sensors (e.g., wheel speed sensors)
  • Battery or charging system issues
  • Faulty body control module (BCM)
  • Incorrectly programmed modules
  • Grounding issues
  • Faulty CAN bus transceiver
  • Software glitches or updates needed

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other related trouble codes. This can provide more context about the issue

  2. 2. Inspect the Wiring and Connectors

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

  3. 3. Repair or Replace

    If any damaged wires or connectors are found, repair or replace them as necessary

  4. 4. Test the CAN Bus

    Multimeter Test: Use a multimeter to check the voltage levels on the CAN High (CAN H) and CAN Low (CAN L) wires. The typical voltage should be around 2.5V when the bus is idle

  5. 5. Scope Test

    If available, use an oscilloscope to analyze the CAN signals for proper waveform patterns

  6. 6. Check for Short Circuits

    Inspect the CAN bus wiring for any short circuits to ground or to each other. This can cause communication failures

  7. 7. Inspect Modules

    Module Functionality: Check the functionality of the modules connected to the CAN bus. A malfunctioning module can disrupt communication

  8. 8. Reprogram or Replace

    If a specific module is found to be faulty, consider reprogramming or replacing it

  9. 9. Check for Interference

    Ensure that there are no aftermarket devices or modifications that could be interfering with the CAN bus communication

  10. 10. Clear Codes and Test Drive

    After performing repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

  11. 11. Professional Diagnosis

    If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with advanced diagnostic tools

  12. 12. Check Battery and Ground Connections

    Ensure that the vehicle's battery is in good condition and that all ground connections are secure, as poor power supply can affect module communication. By following these steps, you should be able to identify and resolve the issue causing the U1704 code. Always remember to take safety precautions when working on a vehicle's electrical system