WOMS
U code network Medium severity

U0012 Medium Speed CAN Communication Bus (+) Open

The OBD2 code U0012 indicates a fault in the medium speed CAN communication bus, specifically an open circuit in the positive line, which can disrupt data transmission between modules

Definition

The OBD2 code U0012 indicates a fault in the medium speed CAN communication bus, specifically an open circuit in the positive line, which can disrupt data transmission between modules

Common causes

  • Open circuit in the CAN bus wiring
  • Faulty CAN bus connector
  • Damaged or corroded wiring
  • Faulty CAN bus module
  • Poor ground connection
  • Short circuit to ground or power
  • Intermittent connection in the CAN bus network
  • Faulty or incompatible aftermarket accessories

Common misdiagnoses

  • Faulty CAN bus wiring
  • Defective CAN bus module
  • Faulty ECU (Electronic Control Unit)
  • Poor ground connections
  • Malfunctioning sensors
  • Battery or power supply issues
  • Incorrectly configured or programmed modules
  • Intermittent connection issues

Troubleshooting steps

  1. 1. Visual Inspection

    Wiring and Connectors: Inspect the wiring harness and connectors associated with the Medium Speed CAN bus for any signs of damage, corrosion, or loose connections. Pay special attention to the connectors at the ECM (Engine Control Module) and other modules on the bus

  2. 2. Ground Connections

    Ensure that all ground connections are secure and free of corrosion

  3. 3. Check for Other Codes

    Use a scan tool to check for any additional trouble codes that may provide more context or indicate related issues. Address any other codes before focusing on U0012

  4. 4. Test the CAN Bus Voltage

    Use a multimeter to measure the voltage on the CAN High (CAN H) and CAN Low (CAN L) wires. The typical voltage levels should be around 2.5V when the bus is idle. If the voltage is significantly off, it may indicate a problem

  5. 5. Inspect Termination Resistors

    Check the termination resistors at both ends of the CAN bus. A missing or faulty resistor can cause communication issues. The typical value for termination resistors is 120 ohms

  6. 6. Perform a Continuity Test

    Use a multimeter to perform a continuity test on the CAN High and CAN Low wires. Look for any breaks in the wiring that could indicate an open circuit

  7. 7. Check for Short Circuits

    Inspect the wiring for any signs of short circuits to ground or to other wires. A short can cause communication failures

  8. 8. Test Modules on the Bus

    If possible, test the individual modules connected to the Medium Speed CAN bus. A faulty module can disrupt communication. You may need to disconnect modules one at a time to isolate the problem

  9. 9. Use a CAN Bus Analyzer

    If available, use a CAN bus analyzer to monitor the communication on the bus. This can help identify if specific messages are being sent or if there are any anomalies

  10. 10. Check for Software Updates

    Sometimes, software issues can cause communication problems. Check if there are any available updates for the vehicle's modules

  11. 11. Consult Wiring Diagrams

    Refer to the vehicle's wiring diagrams to understand the layout of the CAN bus and identify any potential problem areas.1

  12. 12. Professional Diagnosis

    If the issue persists after performing the above steps, consider seeking help from a professional technician or a dealership with advanced diagnostic tools.Conclusion Troubleshooting OBD-II code U0012 requires a systematic approach to identify and resolve issues with the Medium Speed CAN communication bus. By following these steps, you can often pinpoint the source of the problem and take appropriate corrective action