Patent ID: 8393143

Claim:
A method of operating a combustion engine that has in an exhaust gas area at least one SCR-catalyzer with a NH3-filling level, at least one metering device for supplying the SCR-catalyzer with a reactant for reducing nitrous gases, and at least one downstream NH3-sensitive NOx-sensor, the method comprising: determining at least one theoretical NOx-value downstream of the SCR-catalyzer; comparing the at least one theoretical NOx-value to an actual NOx-value downstream of the SCR-catalyzer, wherein an adaptation of the NH3-filling level of the SCR-catalyzer is carried out based on the comparison; and performing a reasonability check of the adaptation by: detecting a first value for at least one comparison parameter that represents a state before a system intervention for adapting the NH3-filling level; performing a first system intervention for adapting the NH3-filling level; detecting a second value of the at least one comparison parameter; performing a second system intervention in an opposite direction of the first system intervention; detecting a third value of the at least one comparison parameter; and comparing the first value, the second value, and the third value, wherein with aid of comparison results of the comparisons of the values, the reasonability, non-reasonability, or non-preciseness of the system interventions are assumed.