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P0685 ECM/PCM Power Relay Control Circuit Short to Ground

The OBD2 code P0685 indicates a short circuit to ground in the power relay control circuit for the Engine Control Module (ECM) or Powertrain Control Module (PCM), which can prevent the ECM/PCM from receiving the...

Definition

The OBD2 code P0685 indicates a short circuit to ground in the power relay control circuit for the Engine Control Module (ECM) or Powertrain Control Module (PCM), which can prevent the ECM/PCM from receiving the necessary power to operate properly

Common causes

  • Shorted wiring or connectors
  • Faulty ECM/PCM
  • Failed power relay
  • Corroded or damaged ground connections
  • Malfunctioning ignition switch
  • Faulty fuses or fuse box issues
  • Poor electrical connections or solder joints

Common misdiagnoses

  • Faulty ECM/PCM
  • Bad power relay
  • Wiring issues or shorts in the harness
  • Battery or charging system problems
  • Ignition switch failure
  • Grounding issues
  • Faulty fuses or fuse box problems
  • Sensor malfunctions

Troubleshooting steps

  1. 1. Check the Code and Freeze Frame Data

    Use an OBD-II scanner to confirm the P0685 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 harness and connectors related to the ECM/PCM power relay. Look for signs of damage, fraying, corrosion, or loose connections

  4. 4. Pay special attention to the ground connections, as a short to ground can often be caused by damaged wires or poor connections

  5. 5. Test the ECM/PCM 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 the Power Supply

    Verify that the ECM/PCM is receiving the correct voltage. Use a multimeter to check the voltage at the relay and the ECM/PCM

  8. 8. Ensure that the battery voltage is adequate and that there are no blown fuses in the circuit

  9. 9. Inspect Ground Connections

    Check the ground connections for the ECM/PCM and the relay. Ensure they are clean, tight, and free of corrosion

  10. 10. Use a multimeter to test for continuity between the ground points and the battery negative terminal

  11. 11. Check for Short Circuits

    Use a multimeter to check for shorts in the wiring harness. Disconnect the ECM/PCM and check the resistance between the power and ground circuits

  12. 12. If you find a short, trace the wiring to locate the source of the short

  13. 13. Examine the ECM/PCM

    If all other components check out, the ECM/PCM itself may be faulty. Consider testing the module or having it reprogrammed or replaced if necessary

  14. 14. Clear the Codes and Test Drive

    After performing repairs, clear the trouble codes using the OBD-II scanner

  15. 15. Take the vehicle for a test drive to see if the code returns. Monitor the vehicle's performance and check for any related symptoms

  16. 16. Consult a Professional

    If you are unable to resolve the issue after these steps, it may be best to consult a professional mechanic or technician who has experience with your specific vehicle make and model.Additional Tips: - Always refer to the vehicle's service manual for specific wiring diagrams and troubleshooting procedures. - Safety first: Disconnect the battery before working on electrical components to avoid shorts or shocks. By following these steps, you should be able to diagnose and potentially resolve the P0685 code effectively