| 摘要 |
PROBLEM TO BE SOLVED: To diagnose whether a thermostat failure is present. SOLUTION: An engine cooling water side temperature sensor 20 is installed in a cooling water circulation line toward the engine 11 side from a thermostat 13, and a radiator side cooling water temperature sensor 21 is installed in the cooling water circulation line on the radiator 15 side. Based on a temperature difference between an engine side cooling water temperature and a radiator side cooling water temperature or temperature variation rate, it is diagnosed whether an opening trouble in which the thermostat 13 is not closed and kept open is present or not in a temperature range in which the thermostat 13 in a normal state is closed. Also, based on the temperature difference between the engine side cooling water temperature and the radiator side cooling water temperature or temperature variation rate, it is diagnosed whether a closed trouble in which the thermostat 13 is not opened and kept closed is present or not in a temperature range in which the thermostat 13 in a normal state is opened. In this case, a determination reference value for trouble determination may be set based on at least one of engine operating state, outside atmospheric temperature, an intake air temperature, and the operating state of an air conditioner. COPYRIGHT: (C)2005,JPO&NCIPI
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