INTERNAL-COMBUSTION-ENGINE DIAGNOSTIC DEVICE

摘要

An internal combustion engine comprises an exhaust purification catalyst (20) and an air-fuel ratio sensor (41) arranged at a downstream side of the exhaust purification catalyst, stops or decreases a feed of fuel as fuel cut control, and controls an air-fuel ratio of exhaust gas to a rich air-fuel ratio after the end of the fuel cut control as post reset rich control. A first characteristic of change of air-fuel ratio at the time the output air-fuel ratio first passes a first air-fuel ratio region X and a second characteristic of change of air-fuel ratio at the time when the output air-fuel ratio first passes a second air-fuel ratio region Y different from the first air-fuel ratio region X are calculated. The diagnosis system judges any one of normality, abnormality, and whether a hold should be put on judgment for the state of the air-fuel ratio sensor, based on the first characteristic of change of air-fuel ratio and, if it is judged that a hold should be put on judgment, judges if the state of the air-fuel ratio sensor is normal or abnormal based on the second characteristic of change of air-fuel ratio. As a result, it is possible to suppress the effects of the change of state of the exhaust purification catalyst while accurately diagnosing the abnormality of deterioration of response of a downstream side air-fuel ratio sensor.