WOMS
U code network Medium severity

U0018 Medium Speed CAN Communication Bus (-) shorted to Bus (+)

The OBD2 code U0018 indicates a fault in the medium speed CAN communication bus, specifically that the negative line of the bus is shorted to the positive line, which can disrupt communication between modules

Definition

The OBD2 code U0018 indicates a fault in the medium speed CAN communication bus, specifically that the negative line of the bus is shorted to the positive line, which can disrupt communication between modules

Common causes

  • Damaged wiring or connectors
  • Short circuit in the CAN bus wiring
  • Faulty CAN bus module
  • Corroded or loose connections
  • Grounding issues
  • Faulty sensors or actuators on the CAN bus
  • Interference from other electrical components

Common misdiagnoses

  • Faulty CAN bus wiring
  • Defective CAN bus module
  • Shorted wiring harness
  • Malfunctioning ECU
  • Incorrectly configured or programmed modules
  • Grounding issues
  • Faulty sensors connected to the CAN bus
  • Intermittent electrical connections

Troubleshooting steps

  1. 1. Scan for Additional Codes

    Use an OBD-II scanner to check for any other related trouble codes. This can provide more context and help identify if other systems are affected

  2. 2. Visual Inspection

    Inspect the wiring and connectors associated with the Medium Speed CAN bus. Look for signs of damage, fraying, corrosion, or loose connections

  3. 3. Check the integrity of the connectors and ensure they are securely connected

  4. 4. Check for Shorts

    Use a multimeter to check for continuity between the CAN High (CAN+) and CAN Low (CAN-) wires. There should be no continuity; if there is, it indicates a short

  5. 5. Inspect the wiring harness for pinched or damaged wires that could be causing a short

  6. 6. Test the CAN Bus Voltage

    Measure the voltage on the CAN High and CAN Low wires with the ignition on (engine off). The typical voltage levels should be around 2.5V to 2.8V for both lines. If they are significantly different, it may indicate a problem

  7. 7. Check Termination Resistors

    Ensure that the termination resistors (typically 120 ohms) are present and functioning correctly at both ends of the CAN bus. A missing or faulty resistor can cause communication issues

  8. 8. Inspect Modules on the Bus

    Identify all modules connected to the Medium Speed CAN bus. Check for any modules that may be malfunctioning or have internal faults, as they can affect the entire bus

  9. 9. Disconnect modules one at a time to see if the code clears or if communication is restored

  10. 10. Check for Ground Issues

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

  11. 11. Use an Oscilloscope

    If available, use an oscilloscope to monitor the CAN signals. This can help identify if the signals are being transmitted correctly and if there are any anomalies

  12. 12. Repair or Replace Damaged Components

    If any damaged wiring, connectors, or modules are found during the inspection, repair or replace them as necessary

  13. 13. 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.1

  14. 14. Seek Professional Help

    If the issue persists after following these steps, consider seeking assistance from a professional mechanic or automotive technician who has experience with CAN bus systems. By following these steps, you should be able to diagnose and potentially resolve the issue related to the U0018 code