DISORDER DIAGNOSIS DEVICE OF AIR-FUEL RATIO SENSOR OF INTERNAL COMBUSTION ENGINE

PURPOSE:To improve the diagnosis precision of an air-fuel ratio by equipping a means to detect the operation state of an internal combustion engine and a means to measure or surmise the temperature of an exhaust system, deciding disorder according to the disorder diagnosis of plural operation spheres on the basis of the detection information of the operation state. CONSTITUTION:An engine main body 101 is equipped with a water temperature sensor 102; a ring gear 103; and a crank angle sensor 104, and downstream of it, an air flow sensor 109; a throttle sensor 110; and an idle rotation speed control valve 111 are equipped. A sensor temperature is surmised from an engine operation state to be sought from a rotation number and load, and the operation state of the engine is measured, and it is judged whether a diagnosis sphere is the one where the reliable responsiveness of an air-fuel ratio sensor 118 can be sought or not. If within the diagnosis sphere, deterioration decision is conducted from the responsiveness of the air-fuel ratio sensor 118. It is decided that the responsiveness is deteriorated when a responding time exceeds a threshold value or voltage change is less than a threshold value.