Patent ID: 7725247

Claim:
An abnormality diagnostic device for an air-fuel ratio sensor that detects an air-fuel ratio of an exhaust gas of an internal combustion engine, comprising: an Electronic Control Unit (ECU) including: an identification portion that models a system extending from a fuel injection valve to the air-fuel ratio sensor by using a first order response delay element, and that identifies at least one parameter of the first order response delay element based on an input based on an input air-fuel ratio given to the air-fuel ratio sensor which occurs when the input air-fuel ratio is sharply changed in accordance with an engine operation requirement, and an output of the air-fuel ratio sensor that changes in response to a change in the input air-fuel ratio; and an abnormality determination portion that determines abnormalities of a response rate and an output of the air-fuel ratio sensor based on the parameter identified by the identification portion.