The catalytic converter has the characteristic that it stores oxygen. The oxygen stored in the lean phase is consumed either fully or in part in the rich phase. Ageing and/or environmental influences reduce the storage capacity of the catalytic converter. With this ageing, the rate of conversion of hydrocarbons is also reduced. Legislation stipulates that the emission of hydrocarbons must not exceed a certain limit. The oxygen storage capacity of the catalytic converter thus enables monitoring of the adherence to limit values.