P0599 OBD II Trouble Code Thermostat Heater Control Circuit High Code

Symptoms of P0599 OBD II Trouble Code

  • The check engine light will illuminate and one of the above codes will be set
  • The temperature gauge may read abnormally high if the thermostat failed in the partially closed position, conversely, it will read lower than normal if the thermostat failed in the full open position

Common Causes of P0599 OBD II Trouble Code

  • A loose or corroded connector on the thermostat
  • A coolant leak will cause the code to set
  • The thermostat itself has failed
  • A short or open has occurred in the wiring harness between the computer and thermostat
  • The Motronic computer has failed