Failure determination device for humidity sensor and control system for exhaust passage changeover valve

There are provided a failure determination device for determining failure of a humidity sensor that detects the humidity of exhaust gases from an internal combustion engine and a control system for an exhaust passage changeover valve. In one form of the invention, it is judged based on a detected operating condition of the engine whether or not the engine is in an operating condition in which failure determination of the humidity sensor can be executed. It is then determined whether or not the humidity sensor has failed, based on a result of detection by the humidity sensor. In another form of the invention, a changeover valve switches an exhaust passage having a catalytic device arranged therein, between a main exhaust passage and a bypass exhaust passage and having an adsorber arranged therein which is capable of adsorbing hydrocarbons and water. A humidity sensor is arranged at a location downstream of the adsorber in the bypass exhaust passage, for detecting humidity of the exhaust gases guided into the bypass exhaust passage. The changeover valve is driven based on a result of the detection.