During the system test, the catalytic converter is fed rich exhaust gas. Rich exhaust gas is low in oxygen; this empties the oxygen accumulators of the catalytic converter. The catalytic converter is then fed lean exhaust gas. Lean exhaust gas is rich in oxygen. This refills the oxygen accumulators of the catalytic converter. When the oxygen accumulators are full, the proportion of oxygen in the exhaust gas after the catalytic converter rises once again. During the system test, it is measured how long it takes before the oxygen accumulators are full. The more oxygen can be accumulated, the better the catalytic converter.