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P code powertrain High severity

P0686 ECM/PCM Power Relay Control Circuit Short to Battery

The OBD2 code P0686 indicates a short circuit in the ECM/PCM power relay control circuit to the battery, which means there is an electrical issue causing the relay to receive constant power, potentially leading to...

Definition

The OBD2 code P0686 indicates a short circuit in the ECM/PCM power relay control circuit to the battery, which means there is an electrical issue causing the relay to receive constant power, potentially leading to improper operation of the engine control module (ECM) or powertrain control module (PCM)

Common causes

  • Shorted wiring or connectors
  • Faulty ECM/PCM
  • Defective power relay
  • Poor ground connection
  • Corroded or damaged terminals
  • Malfunctioning ignition switch
  • Battery issues or poor battery connections

Common misdiagnoses

  • Faulty ECM/PCM
  • Bad power relay
  • Wiring issues or shorts in the harness
  • Battery problems
  • Faulty ignition switch
  • Corroded connectors
  • Grounding issues

Troubleshooting steps

  1. 1. Check the Code and Freeze Frame Data

    Use an OBD-II scanner to confirm the P0686 code and check for any additional codes that may provide more context

  2. 2. Review freeze frame data to understand the conditions under which the code was set

  3. 3. Inspect the Wiring and Connectors

    Visually inspect the wiring and connectors related to the ECM/PCM power relay. Look for signs of damage, corrosion, or loose connections

  4. 4. Pay special attention to the wiring harness that connects to the ECM/PCM and the power relay

  5. 5. Test the Power Relay

    Locate the ECM/PCM power relay in the fuse box or relay panel

  6. 6. Test the relay using a multimeter to check for continuity and proper operation. You can also swap it with a known good relay to see if the issue persists

  7. 7. Check for Short Circuits

    Use a multimeter to check for continuity between the relay control circuit and battery voltage. A short circuit may exist if there is continuity where there shouldn't be

  8. 8. Inspect the wiring for any signs of fraying or contact with metal surfaces that could cause a short

  9. 9. Inspect the ECM/PCM

    If the wiring and relay are in good condition, the issue may lie within the ECM/PCM itself. Check for any signs of damage or water intrusion

  10. 10. If possible, test the ECM/PCM in another vehicle or replace it with a known good unit to see if the problem resolves

  11. 11. Check Fuses

    Inspect the fuses related to the ECM/PCM and the power relay. Replace any blown fuses and check if the code reappears

  12. 12. Clear the Code and Test Drive

    After performing the above checks and repairs, clear the code using the OBD-II scanner

  13. 13. Take the vehicle for a test drive to see if the code returns. Monitor the vehicle's performance and any warning lights

  14. 14. Consult a Professional

    If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has access to advanced diagnostic tools and equipment.Additional Tips: - Always refer to the vehicle's service manual for specific wiring diagrams and troubleshooting procedures. - Ensure that the battery and charging system are functioning properly, as low voltage can sometimes trigger false codes. By following these steps, you should be able to identify and resolve the issue related to the P0686 code