Patent ID: 8794056

Claim:
An abnormality determination device for an air-fuel ratio sensor, comprising: a differential value calculator configured to calculate a differential value of an output value of the air-fuel ratio sensor which is configured to detect an air-fuel ratio of exhaust gas; and an abnormality determiner configured to determine abnormality of the air-fuel ratio sensor based on a result of comparison between a reference output value of the air-fuel ratio sensor and a predetermined threshold, the reference output value being obtained by the air-fuel ratio sensor when the differential value calculated by the differential value calculator becomes a predetermined value, wherein the abnormality determiner determines abnormality of the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas changes from rich to lean with respect to a theoretical exhaust gas air-fuel ratio which is an exhaust gas air-fuel ratio corresponding to a theoretical air-fuel ratio of air-fuel mixture, passing through the theoretical exhaust gas air-fuel ratio, in accordance with at least one of start and termination of a fuel-cut operation that stops supply of fuel to an internal combustion engine.