Patent ID: 8145409

Claim:
A method for determining degradation of an exhaust gas sensor positioned in an exhaust system for an internal combustion engine of a vehicle, comprising: modulating an air/fuel ratio of gas exhausted by the internal combustion engine to the exhaust gas sensor through at least one rich-to-lean transition and at least one lean-to-rich transition; indicating a degradation condition of the exhaust gas sensor in response to at least both a delayed response of the exhaust gas sensor to one of the transitions and asymmetry of the exhaust gas sensor response among a rich-to-lean response duration and a lean-to-rich response duration of the exhaust gas sensor; indicating the degradation condition of the exhaust gas sensor in response to at least one of a rich-to-lean response duration of the exhaust gas sensor and a lean-to-rich response duration of the exhaust gas sensor being greater than a delay threshold; and indicating the degradation condition of the exhaust gas sensor in response to a ratio of the rich-to-lean response duration to the lean-to-rich response duration being greater than an asymmetry threshold that is relative to an axis of symmetry of the rich-to-lean response duration versus the lean-to-rich response duration.