Abnormality diagnosis device of thermostat

An abnormality diagnosis device of a thermostat that opens and closes a cooling water passage, according to a temperature of cooling water of an engine, and switches between availability and unavailability of flow of the cooling water to a heat release device, comprising:

• circuitry configured to
• detect the temperature of the cooling water on a basis of a sensor signal of a cooling water temperature sensor,
• detect an abnormality of the thermostat, when the temperature of the cooling water reaches a first reference temperature at which warm-up of the engine is completed and thereafter decreases from the first reference temperature to fall below an abnormality determination reference temperature that is lower than the first reference temperature, and
• prevent decrease of the temperature of the cooling water to the abnormality determination reference temperature before the temperature of the cooling water reaches the abnormality determination reference temperature, when the temperature of the cooling water first reaches the first reference temperature at which the warm-up of the engine is completed and thereafter decreases from the first reference temperature to fall below a second reference temperature, wherein
• the second reference temperature is set to start a control to prevent the decrease of the temperature of the cooling water, and
• the second reference temperature is lower than the first reference temperature and is higher than the abnormality determination reference temperature.

An abnormality diagnosis device of a thermostat that opens and closes a cooling water passage, according to a temperature of cooling water of an engine, and switches between availability and unavailability of flow of the cooling water to a heat release device, comprising:

• a temperature detection module that detects the temperature of the cooling water on a basis of a sensor signal of a cooling water temperature sensor;
• an abnormality determination module that detects an abnormality of the thermostat, when the temperature of the cooling water reaches a first reference temperature at which warm-up of the engine is completed and thereafter decreases from the first reference temperature to fall below an abnormality determination reference temperature that is lower than the first reference temperature;
• and
• a cooling water temperature adjustment module that halts a fuel cut control for preventing temperature decrease of the cooling water before the temperature of the cooling water reaches the abnormality determination reference temperature, when the temperature of the cooling water first reaches the first reference temperature at which the warm-up of the engine is completed and thereafter decreases from the first reference temperature to fall below a second reference temperature in a fuel cut control state of the engine,
• wherein
• the second reference temperature is set to start a control to prevent the decrease of the temperature of the cooling water, and
• the second reference temperature is lower than the first reference temperature and higher than the abnormality determination reference temperature.