INTERNAL-COMBUSTION-ENGINE DIAGNOSTIC DEVICE

摘要

This internal combustion engine is equipped with an exhaust purification catalyst (20) and an air-fuel-ratio sensor (41) positioned on the downstream side of the exhaust-purification catalyst, and executes a fuel-cut control for stopping or reducing the supply of fuel, and a post-recovery rich control for controlling, after completing the fuel-cut control, the exhaust air-fuel ratio so as to be a rich air-fuel ratio. On the basis of the output air-fuel ratio outputted from the air-fuel-ratio sensor, a diagnostic device calculates first air-fuel-ratio-change properties and second air-fuel-ratio-change properties at the times when, after completing the fuel-cut control, the output air-fuel ratio first passes through a first air-fuel-ratio region (X) leaner than the theoretical air-fuel ratio and a second air-fuel-ratio region (Y) which includes the theoretical air-fuel ratio. The diagnostic device diagnoses an abnormality of the air-fuel-ratio sensor on the basis of the first air-fuel-ratio-change properties and the second air-fuel-ratio-change properties. As a result, it is possible to minimize the impact of changes to the state of the exhaust purification catalyst, and accurately diagnose a responsiveness-deterioration abnormality of the downstream-side air-fuel-ratio sensor.