| 摘要 |
PROBLEM TO BE SOLVED: To appropriately curb an erroneous diagnosis in a thermostat failure diagnosis process.SOLUTION: An ECU 200 performs a thermostat opening failure diagnosis process when a thermostat diagnosis prerequisite is met. The ECU determines whether or not a detection value of an engine outlet water temperature ECT is shifted from an increase to a decrease not only by whether or not a first water temperature change rate &Dgr;ECT1 with a short calculation cycle is less than a predetermined value α (S22) but also by whether or not a second water temperature change rate &Dgr;ECT2 with a long calculation cycle is less than a predetermined value &bgr; (&bgr;<α) (S23). When at least either of the determination results shows that an ECT detection value is shifted from the increase to the decrease, the ECU determines that the thermostat diagnosis prerequisite is not met (S25) and prohibits the thermostat opening failure diagnosis process. |
