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 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 first moderated signal by applying a first moderation calculation to the detection signal, and a second moderated signal by applying a second moderation calculation to the detection signal; calculating a deviation between the first and second moderated signals; and determining whether the gas sensor is in the abnormal state on the basis of the deviation obtained during the diagnosis period.
