WOMS
P code powertrain Medium severity

P0599 Thermostat Control Circuit Intermittent

The OBD2 code P0599 indicates that there is an intermittent issue with the thermostat control circuit, which may affect the engine's ability to regulate temperature properly

Definition

The OBD2 code P0599 indicates that there is an intermittent issue with the thermostat control circuit, which may affect the engine's ability to regulate temperature properly

Common causes

  • Faulty thermostat
  • Wiring issues (damaged or corroded wires)
  • Poor connections or loose connectors
  • Malfunctioning engine control module (ECM)
  • Failed thermostat housing
  • Short circuit in the thermostat control circuit
  • Faulty temperature sensor

Common misdiagnoses

  • Faulty thermostat
  • Wiring issues
  • Engine coolant temperature sensor failure
  • PCM (Powertrain Control Module) malfunction
  • Cooling system leaks
  • Radiator issues
  • Faulty temperature gauge
  • Air pockets in the cooling system

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide more context and help identify related issues

  2. 2. Inspect the Thermostat

  3. 3. Check the thermostat for proper operation. A stuck open or closed thermostat can cause temperature regulation issues

  4. 4. If the thermostat is faulty, replace it

  5. 5. Examine the Wiring and Connectors

  6. 6. Inspect the wiring and connectors associated with the thermostat and the thermostat control circuit for any signs of damage, corrosion, or loose connections

  7. 7. Repair or replace any damaged wiring or connectors

  8. 8. Test the Thermostat Sensor

  9. 9. If the vehicle has a separate temperature sensor for the thermostat, test it for proper resistance and functionality

  10. 10. Replace the sensor if it is found to be faulty

  11. 11. Check the Engine Coolant Level

  12. 12. Ensure that the engine coolant is at the proper level. Low coolant levels can affect thermostat operation and lead to erroneous readings

  13. 13. Inspect the Engine Control Module (ECM)

  14. 14. If all other components check out, there may be an issue with the ECM itself. Check for software updates or reprogramming if necessary

  15. 15. In some cases, the ECM may need to be replaced if it is determined to be faulty

  16. 16. Clear the Codes and Test Drive

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

  18. 18. Monitor Live Data

  19. 19. Use the OBD-II scanner to monitor live data while the engine is running. Check the coolant temperature readings and thermostat operation to ensure they are within normal ranges

  20. 20. Consult Technical Service Bulletins (TSBs)

  21. 21. Check for any TSBs related to the P0599 code for your specific vehicle make and model. Manufacturers may have specific recommendations or known issues

  22. 22. Seek Professional Help

  23. 23. If you are unable to diagnose or resolve the issue, consider seeking help from a qualified mechanic or automotive technician who has experience with OBD-II diagnostics. By following these steps, you should be able to identify the cause of the P0599 code and take appropriate action to resolve the issue