The invention is directed to a method for protecting a catalyzer against overheating. The method includes the steps of checking whether an injection valve no longer correctly closes by means of a conventional diagnostic process. If the condition is present that an injection valve no longer correctly closes, the air/fuel mixture for all cylinders is enriched and an overrun switchoff is inhibited. The method leads to the condition that in all load ranges, the oxygen quantity reaching the catalyzer is limited so that no damaging afterburning can take place. In this way, the catalyzer is protected against overheating and the affected vehicle is not disabled.