Patent ID: 6925796
Filing Date: 2005-08-09
Classification: F01N,F02D,G01N,Y02T

Abstract:
1. A method for diagnosing degradation of an emission control system coupled downstream of an internal combustion engine, the system including a NOx catalyst having a first NOx sensor coupled upstream of the catalyst and a second NOx sensor coupled downstream of the catalyst, the method comprising: providing an indication of an operating condition; in response to said indication diagnosing the first NOx sensor degradation if a difference between a first NOx sensor signal and an estimated amount of NOx in an exhaust gas mixture upstream of the catalyst is greater than a first predetermined value; and diagnosing the second NOx sensor degradation if a difference between a first NOx sensor signal and an estimated amount of NOx in an exhaust gas mixture upstream of the catalyst is less than said first predetermined value and a difference between said first NOx sensor signal and a second NOx sensor signal is greater than a second predetermined value.