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P code powertrain Medium severity

P066C Cylinder 2 Glow Plug Control Circuit Low

The OBD2 code P066C indicates a low voltage or malfunction in the glow plug control circuit for cylinder 2, which can affect the engine's ability to start and run efficiently in cold conditions

Definition

The OBD2 code P066C indicates a low voltage or malfunction in the glow plug control circuit for cylinder 2, which can affect the engine's ability to start and run efficiently in cold conditions

Common causes

  • Faulty glow plug
  • Damaged wiring or connectors
  • Failed glow plug control module
  • Short circuit in the glow plug circuit
  • Open circuit in the glow plug circuit
  • Poor ground connection
  • Faulty engine control module (ECM)

Common misdiagnoses

  • Faulty glow plug
  • Bad glow plug relay
  • Wiring issues or shorts in the circuit
  • Faulty engine control module (ECM)
  • Incorrectly installed or damaged glow plug harness
  • Fuel system issues
  • Injector problems
  • Compression issues in the cylinder

Troubleshooting steps

  1. 1. Check for Additional Codes

    Before proceeding, check for any other related trouble codes that may provide more context to the issue. Addressing all codes can help in diagnosing the problem more effectively

  2. 2. Inspect the Glow Plug

  3. 3. Remove the glow plug for cylinder 2 and inspect it for damage or excessive wear. A faulty glow plug can cause low voltage readings

  4. 4. Test the glow plug with a multimeter to ensure it has the correct resistance (typically around 0.5 to 2 ohms, but check the specifications for your vehicle)

  5. 5. Check the Glow Plug Control Module

  6. 6. Inspect the glow plug control module (if equipped) for any signs of damage or corrosion

  7. 7. Ensure that the module is receiving the correct voltage and is functioning properly

  8. 8. Inspect Wiring and Connectors

  9. 9. Check the wiring and connectors leading to the glow plug and the control module for any signs of damage, corrosion, or loose connections

  10. 10. Look for frayed wires, broken connectors, or any signs of short circuits

  11. 11. Test the Glow Plug Relay

  12. 12. If your vehicle uses a relay to control the glow plugs, test the relay to ensure it is functioning correctly. A faulty relay can prevent the glow plugs from receiving power

  13. 13. Check Power and Ground

  14. 14. Use a multimeter to check for proper voltage at the glow plug connector when the ignition is turned on. You should see battery voltage

  15. 15. Ensure that the ground connection for the glow plug circuit is solid and free of corrosion

  16. 16. Inspect Engine Control Module (ECM)

  17. 17. If all other components check out, there may be an issue with the ECM. Ensure that the ECM is functioning properly and is not sending incorrect signals to the glow plug circuit

  18. 18. Clear Codes and Test Drive

  19. 19. After performing the necessary repairs, clear the trouble codes using an OBD-II scanner and take the vehicle for a test drive to see if the code returns

  20. 20. Consult a Professional

  21. 21. If you are unable to diagnose or fix the issue after these steps, it may be best to consult a professional mechanic who has experience with diesel engines and glow plug systems. By following these steps, you should be able to identify and resolve the issue related to the P066C code. Always refer to your vehicle's service manual for specific procedures and specifications