Malfunction diagnostic apparatus and malfunction diagnostic method for intake air temperature sensors

A malfunction diagnostic apparatus for intake air temperature sensors provided in an intake passage of an internal combustion engine at any two different positions in a longitudinal direction of the intake passage, wherein each of the intake air temperature sensors detects an intake air temperature used for a control for the internal combustion engine, and the intake air temperature sensors include a first intake air temperature sensor and a second intake air temperature sensor, the malfunction diagnostic apparatus comprising:

• a coolant temperature sensor that detects a coolant temperature that is a temperature of a coolant of the internal combustion engine;
• a first determination portion that determines that a precondition for performing a malfunction diagnosis is satisfied, if both of a first condition and a second condition are satisfied when a process of starting the internal combustion engine is started, wherein the first condition is a condition that the coolant temperature detected by the coolant temperature sensor is determined to be equal to the intake air temperature detected by the second intake air temperature sensor provided at a portion of the intake passage, which is more likely to be cooled than a portion of the intake passage at which the first intake air temperature sensor is provided, and the second condition is a condition that the coolant temperature decreases by a decrease amount that is equal to or larger than a preset value that is set in advance, during a time period from a time point at which a process of stopping the internal combustion engine is completed, to a time point at which the process of starting the internal combustion engine is started;
• a second determination portion that makes a tentative determination as to whether a malfunction occurs in at least one of the first and second intake air temperature sensors, if the first determination portion determines that the precondition is satisfied when the process of starting the internal combustion engine is started, wherein the second determination portion makes the tentative determination that the first and second intake air temperature sensors normally function, if a difference between the intake air temperatures detected by the first and second intake air temperature sensors is equal to or smaller than a reference value that is set in advance, and the second determination portion makes the tentative determination that a malfunction occurs in at least one of the first and second intake air temperature sensors, if the difference between the intake air temperatures detected by the first and second intake air temperature sensors is larger than the reference value;
• and
• a third determination portion that determines that the tentative determination is an invalid determination, if at least one of the intake air temperatures detected by the first and second intake air temperature sensors changes during a given time period that starts at the time point at which the process of starting the internal combustion engine is started, and determines that the tentative determination is a valid determination, if neither of the intake air temperatures detected by the first and second intake air temperature sensors changes during the given time period.