INTERNAL-COMBUSTION-ENGINE DIAGNOSTIC DEVICE

摘要

This internal combustion engine is equipped with an exhaust purification catalyst (20) capable of occluding oxygen in introduced exhaust gas and positioned in the exhaust channel of the internal combustion engine, and an air-fuel-ratio sensor (41) for detecting the air-fuel ratio of the exhaust gas discharged from the exhaust purification catalyst and positioned on the downstream side of the exhaust-purification catalyst in the direction of exhaust flow. The internal combustion engine executes a fuel-cut control for stopping or reducing the supply of fuel to a fuel chamber (5). An abnormality diagnostic device calculates air-fuel-ratio-change properties on the basis of the output air-fuel ratio at the times when, after completing the fuel-cut control, the output air-fuel ratio outputted by the air-fuel-ratio sensor first passes through a part of an air-fuel-ratio region at or above the theoretical air-fuel ratio. The abnormality diagnostic device diagnoses an abnormality of the air-fuel-ratio sensor on the basis of the air-fuel-ratio-change properties. As a result, it is possible to definitively diagnose a responsiveness-deterioration abnormality of the downstream-side air-fuel-ratio sensor if necessary when the fuel-cut control has been performed.