| 摘要 |
<P>PROBLEM TO BE SOLVED: To increase abnormality detecting accuracy of a thermostat provided in an engine cooling water circulating circuit. Ž<P>SOLUTION: When such thermostat opening abnormality that the thermostat 19 is not closed and is left open although cooling water temperature is in a non-warmed up temperature range occurs, a relationship that the variation of a cooling water temperature detected value is reduced as vehicle speed is accelerated (the amount of increase is reduced or the amount of decrease is increased) is established between the vehicle speed and the variation of the cooling water temperature detected value detected by a cooling water temperature sensor 20. Taking note of such a characteristic, it is determined whether or not there is a correlation during thermostat abnormality between the vehicle speed and the variation of the cooling water temperature detected value in the non-warmed up water temperature range, thereby performing a first abnormality diagnosis for determining the presence or absence of the thermostat opening abnormality. Further, a second abnormality diagnosis for determining the presence or absence of the thermostat opening abnormality is performed using the cooling water temperature detected value and a cooling water temperature estimate value. When the results of abnormality diagnoses in the first and second abnormality diagnoses are the same, the result of the abnormality diagnosis is fixed as the final result of the abnormality diagnosis. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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