Desulfuration of a NOx trap

The method involves setting a long lean period (18) for increasing oxygen storage capacity parameter of a nitrogen oxide trap, where the long lean period has duration that ranges between 20 and 60 seconds. An end of the short lean period (17) is determined by applying a law, where the short lean period has duration that ranges between 5 and 30 seconds. An end of rich period (16) is determined by applying the law for restarting a short lean period. An independent claim is also included for a power train of a motor vehicle.