Abstract: To estimate an engine cooling water temperature, four learned neural networks (150A, 150B, 150C, and 150D) are stored, in which weights are learned for the four states of whether the grille shutter (50) is opened and whether air blown by the blower (63) circulates through the air-conditioning use heater (65). The engine cooling water temperature is estimated using any one of the learned neural networks selected from among the four learned neural networks (150A, 150B, 150C, and 150D). An abnormality of the engine cooling water recirculation system is detected based on the estimated value of the engine cooling water temperature.

Abstract: To estimate an engine cooling water temperature, four learned neural networks (150A, 150B, 150C, and 150D) are stored, in which weights are learned for the four states of whether the grille shutter (50) is opened and whether air blown by the blower (63) circulates through the air-conditioning use heater (65). The engine cooling water temperature is estimated using any one of the learned neural networks selected from among the four learned neural networks (150A, 150B, 150C, and 150D). An abnormality of the engine cooling water recirculation system is detected based on the estimated value of the engine cooling water temperature.

Abstract: A misfire determination apparatus includes a rotation variation amount acquisition unit that obtains a rotation variation amount (?NE), which is a difference between a first angular velocity variation amount (??1) obtained during an expansion stroke of an arbitrary cylinder of a multi-cylinder internal combustion engine and a second angular velocity variation amount (??2) having been obtained in relation to a cylinder that has reached the expansion stroke N (where N is a positive integer) revolutions of a crankshaft before the arbitrary cylinder reaches the expansion stroke, and a misfire determination unit that, when the obtained rotation variation amount (?NE) exceeds a predetermined threshold (?NEth), determines that a misfire has not occurred in the internal combustion engine when a predetermined condition is established, and determines that a misfire has occurred in the internal combustion engine when the predetermined condition is not established.

Abstract: After a system-off state has continued for a preset, time period since a system-off operation, on satisfaction of abnormality diagnosis prerequisites including a condition that a warm-up determination parameter indicating a degree of warm-up of an engine at a system-off time is equal to or greater than a predetermined value, characteristic abnormality diagnosis is performed to determine whether a characteristic abnormality occurs in a fuel pressure sensor. For a time period from a system-on operation to a system-off operation, the warm-up determination parameter is incremented when the engine is in operation, while being decremented after satisfaction of a predetermined condition when the engine is not in operation.

Abstract: After a system-off state has continued for a preset, time period since a system-off operation, on satisfaction of abnormality diagnosis prerequisites including a condition that a warm-up determination parameter indicating a degree of warm-up of an engine at a system-off time is equal to or greater than a predetermined value, characteristic abnormality diagnosis is performed to determine whether a characteristic abnormality occurs in a fuel pressure sensor. For a time period from a system-on operation to a system-off operation, the warm-up determination parameter is incremented when the engine is in operation, while being decremented after satisfaction of a predetermined condition when the engine is not in operation.

Abstract: A misfire determination apparatus includes a rotation variation amount acquisition unit that obtains a rotation variation amount (?NE), which is a difference between a first angular velocity variation amount (??1) obtained during an expansion stroke of an arbitrary cylinder of a multi-cylinder internal combustion engine and a second angular velocity variation amount (??2) having been obtained in relation to a cylinder that has reached the expansion stroke N (where N is a positive integer) revolutions of a crankshaft before the arbitrary cylinder reaches the expansion stroke, and a misfire determination unit that, when the obtained rotation variation amount (?NE) exceeds a predetermined threshold (?NEth), determines that a misfire has not occurred in the internal combustion engine when a predetermined condition is established, and determines that a misfire has occurred in the internal combustion engine when the predetermined condition is not established.