Patent Number: 6,167,695

Title: Method and system for diagnosing deterioration of NOx catalyst

Abstract: A system and method for diagnosing deterioration of a nitrogen oxide (NOx) catalyst for an internal combustion engine. An output signal indicative of concentration of nitrogen oxides (NOx) in exhaust gas passing through the NOx catalyst is generated from a NOx sensor. Rates of change in the detected NOx concentration are calculated a plurality of times over a predetermined period of time after an air/fuel ratio becomes less than a stoichiometric air/fuel ratio. A representative value derived from the calculated rates of change in the detected NOx concentration is compared with a predetermined reference value for determining that the NOx catalyst is deteriorated.

Inventors: Itou; Yasuyuki (Yokohama, JP), Itou; Hidetoshi (Yokohama, JP), Ishihara; Kouji (Yokohama, JP)

Assignee: Nissan Motor Co., Ltd.

International Classification: B01D 53/94 (20060101); F01N 3/08 (20060101); F01N 11/00 (20060101); F01N 003/00 ()

Expiration Date: 01/02/2018