Fault diagnosis method of thermostat

A fault diagnosis method of a thermostat, comprising:

• confirming, by a controller, whether a flow stop valve is equipped in a vehicle;
• when the controller confirms that the flow stop valve is equipped in the vehicle, diagnosing, by the controller, whether an operation of the flow stop valve is normal, wherein the diagnosing of whether the operation of the flow stop valve is normal includes:
• deriving, by the controller, a model value of a temperature of cooling water, and
• deriving an actual temperature value of the cooling water by measuring the temperature of the cooling water using a temperature sensor;
• confirming, by the controller, whether the diagnosing of whether the operation of the flow stop valve is normal ends;
• and
• when the controller confirms that the diagnosing of whether the operation of the flow stop valve is normal ends, diagnosing, by the controller, whether an operation of the thermostat is faulty or normal, wherein the diagnosing of whether the operation of the thermostat is faulty or normal includes:
• comparing, by the controller, the values derived in the deriving of the actual temperature value with values previously input to the controller, wherein the comparing depends on whether the controller diagnoses the operation of the flow stop valve as being normal, and
• when the controller diagnoses the operation of the flow stop valve as being normal and determines that a value obtained by adding a predetermined margin previously input to the controller to the model value is below a minimum value of the actual temperature of the cooling water after the operation of the flow stop valve, diagnosing, by the controller, the operation of the thermostat as being normal.