Patent ID: 8215098

Claim:
A system for diagnosing operation of an exhaust gas aftertreatment component for an internal combustion engine, the system comprising: a NOx sensor producing a NOx signal indicative of NOx content of exhaust gas exiting the aftertreatment component, and a control circuit estimating as a function of a number of engine operating conditions a NOx inlet content corresponding to a NOx content of exhaust gas produced by the engine and entering the aftertreatment component, the control circuit determining a lean NOx conversion efficiency of the aftertreatment component as a function of the NOx signal and of the NOx inlet content and determining that the aftertreatment component is not saturated if the lean NOx conversion efficiency is greater than a first minimum efficiency value and the lean NOx conversion efficiency does not drop below a second minimum efficiency value for more than a first predefined time period, the control circuit responsive to an indicator indicating that regeneration of the aftertreatment component is occurring to determine a NOx conversion efficiency of the aftertreatment component as a function of the NOx signal and of the NOx inlet content and to determine that the aftertreatment component is degraded if the NOx conversion efficiency is below a threshold value, only if the aftertreatment component is not saturated.