ABNORMALITY DIAGNOSIS SYSTEM OF AIR-FUEL RATIO SENSOR

An abnormality diagnosis system which can reliably detect a crack of element of an air-fuel ratio sensor. An abnormality diagnosis system of limit current type air-fuel ratio sensors (40, 41) provided in the exhaust passage of the internal combustion engine comprises a current detecting part (61) detecting an output current of an air-fuel ratio sensor and a sensor temperature control device controlling the temperature of the air-fuel ratio sensor. The abnormality diagnosis system uses the current detecting part (61) to detect the output current of the air-fuel ratio sensor when the air-fuel ratio is made the rich air-fuel ratio in the state where temperature of the air-fuel ratio is made the first temperature and when the air-fuel ratio is made the rich air-fuel ratio in the state where the temperature of the air-fuel ratio is made a second temperature higher than the first temperature. It is judged that the air-fuel ratio sensor is abnormal if the output current when the temperature of the air-fuel ratio sensor is the first temperature is larger than the output current when it is the second temperature by a predetermined value or more.