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U1900 CAN Communication Bus Fault

The OBD2 code U1900 indicates a fault in the CAN (Controller Area Network) communication bus, suggesting a communication issue between modules in the vehicle's network

Definition

The OBD2 code U1900 indicates a fault in the CAN (Controller Area Network) communication bus, suggesting a communication issue between modules in the vehicle's network

Common causes

  • Faulty CAN bus wiring or connectors
  • Short circuit in the CAN bus
  • Open circuit in the CAN bus
  • Faulty control module
  • Poor ground connections
  • Interference from other electrical components
  • Corroded or damaged connectors
  • Software issues or bugs in the control module
  • Low battery voltage or power supply issues
  • Faulty termination resistors

Common misdiagnoses

  • Faulty Engine Control Module (ECM)
  • Faulty Transmission Control Module (TCM)
  • Bad wiring or connectors
  • Faulty Body Control Module (BCM)
  • Defective sensors
  • Battery or charging system issues
  • Faulty CAN bus termination resistors
  • Software or firmware issues in modules
  • Grounding issues
  • Intermittent electrical connections

Troubleshooting steps

  1. 1. Check for Other Codes

    Use an OBD-II scanner to check for any additional trouble codes. Other codes may provide more context about the issue

  2. 2. Inspect the Wiring and Connectors

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

  3. 3. Connector Integrity

    Ensure that all connectors are securely attached and free of corrosion

  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 levels should be around 2.5V when idle

  5. 5. Scope Test

    If available, use an oscilloscope to check the signal integrity on the CAN bus. Look for clean square wave signals

  6. 6. Check for Short Circuits

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

  7. 7. Inspect Modules

    Module Functionality: Check if any modules on the CAN bus are malfunctioning. A faulty module can disrupt communication

  8. 8. Power and Ground

    Ensure that all modules have proper power and ground connections

  9. 9. Look for Intermittent Issues

    Sometimes, the issue may be intermittent. Pay attention to when the code appears (e.g., during specific driving conditions or after certain actions)

  10. 10. Check for Software Updates

    Verify if there are any software updates available for the vehicle’s modules. Sometimes, manufacturers release updates to fix communication issues

  11. 11. Clear Codes and Test Drive

    After performing inspections and repairs, clear the codes and take the vehicle for a test drive to see if the code returns

  12. 12. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the U1900 code for your specific vehicle make and model. Manufacturers may have specific recommendations for addressing this issue

  13. 13. Professional Diagnosis

    If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with experience in diagnosing CAN bus issues. By following these steps, you should be able to identify and resolve the underlying cause of the U1900 code