Importance

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Abstract

In a thermostat failure diagnosis apparatus for an internal combustion engine in which a failure diagnosis of a thermostat can be effectively made, in the case where, after starting of the engine, an intake air quantity of the engine or a parameter related to the intake air quantity is equal to or higher than a predetermined value, and a cooling water temperature is equal to or higher than an intake air temperature (outside air temperature), on the basis of a time in which a rising quantity in the cooling water temperature at an upstream side of the thermostat reaches a predetermined value, or a time in which the cooling water temperature rises to a predetermined temperature, the failure of the thermostat is judged. By this, the failure diagnosis is not made in the state where an engine generating heat quantity is small so that there is a fear that an erroneous diagnosis occurs, and the failure diagnosis of the thermostat can be rationally made only in the state where the engine generating heat quantity is large to some degree so that there is no fear of erroneous diagnosis.

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First Claim