Patent ID: 7954364

Claim:
A malfunction diagnosis apparatus for performing a malfunction diagnosis of an exhaust gas sensor, which is for detecting at least one of an air-fuel ratio and a rich-lean state and provided on a downstream side of a catalyst, which is for purifying exhaust gas of an internal combustion engine, the malfunction diagnosis apparatus comprising: dead time determination means for determining a dead time between a first time point, at which fuel cut of the internal combustion engine is started, and a second time point, at which the fuel cut starts exerting effect on an output of the exhaust gas sensor; output change time measurement means for measuring an output change time between the first time point and a third time point, at which the output of the exhaust gas sensor changes to a leaner side than a threshold; and malfunction determination means for determining whether a malfunction is caused in the exhaust gas sensor on the basis of a response time of the exhaust gas sensor obtained by subtracting the dead time from the output change time.