Method to control the exhaust gas treating of a direct injection Otto engine and of a lean-burn engine

Exhaust gas temperature (1) is measured. In lean running, this provides an indication of storage catalyst loading. Preferred features: One or more further operational parameters are used in forming the indication of storage catalyst loading. These include time since last rich-to-lean running transition, torque/Pme fluctuation, or injection timing. Exhaust gas temperature differential, measured between rich- and lean running, gives the required indication. A further parameter employed, is as cited previously. Temperature and temperature gradient of the exhaust gases are measured, the latter forming the required indication. A further operational parameter is selected as before.