Patent attributes
A gas sensor diagnostic method includes the steps of counting the reversal number of times that a target air-fuel ratio for an air-fuel mixture to be supplied to an internal combustion engine reverses from a rich side to a lean side or from the lean side to the rich side through a specific air-fuel ratio defined as a boundary of the rich and lean sides; obtaining a detection signal of a gas sensor at constant time intervals during a diagnosis period between a timing when the count for the reversal number is started and a timing when the reversal number reaches a predetermined number; calculating a moderated signal by applying a moderation calculation using a predetermined moderation coefficient to the obtained detection signal; calculating a deviation between the obtained detection signal and the calculated moderated signal; and determining whether the gas sensor is in an abnormal state or not on the basis of the deviation.
