In control systems (5) for internal combustion engines (14) in motor vehicles it is known that fault diagnoses are carried out to ensure the functional reliability of the internal combustion engine (14) or the motor vehicle even in the event of a fault. If a fault symptom (1) occurs, the cause of the fault is determined and a diagnosis manager (3) is used as a rule to deactivate the defective control system (5) completely or to initiate an emergency operation function. It is proposed that all information relating to fault symptoms should be listed, the actual cause should be determined by comparison with stored fault profiles and as a result only the smallest possible restriction of the functions of the relevant control systems (5) should be initiated. This has the advantage that the control system (5) can as a rule continue to be operated despite their restricted functional scope.