Abnormality detecting system for oxygen sensor and abnormality detecting method

摘要

An abnormality detecting system and method detect an abnormality in an oxygen sensor provided on a downstream side of a catalyst for purifying exhaust gas released from an internal combustion engine. An upstream side sensor is provided on an upstream side of the catalyst, and produces an output corresponding to an exhaust air-fuel ratio. A theoretical oxygen storage capacity of the catalyst is obtained, for example, by determining an amount of oxygen in the exhaust gas flowing into the catalyst during a period in which the oxygen sensor produces a rich output and the upstream side sensor produces a lean output. An abnormality in the oxygen sensor is detected to exist when the theoretical oxygen storage capacity has exceeded a maximum oxygen storage amount of the catalyst.