ABNORMALITY DIAGNOSIS SYSTEM OF AIR-FUEL RATIO SENSOR

An abnormality diagnosis system of an air-fuel ratio sensor 40 or 41 provided in an exhaust passage of an internal combustion engine and generating a limit current corresponding to an air-fuel ratio, comprises a current detecting part 61 detecting an output current of the air-fuel ratio sensor and an applied voltage control device 60 controlling a voltage applied to the air-fuel ratio sensor. The abnormality diagnosis system applies a voltage inside a limit current region where a limit current is generated and a voltage outside the limit current region to the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas circulating around the air-fuel ratio sensor is made a predetermined constant air-fuel ratio, and judges a type of abnormality occurring at the air-fuel ratio sensor based on an output current of the air-fuel ratio sensor detected by the current detecting part at this time.