VDI/VDE 2650 part 7 lists the most important application-specific faults and fault conditions for actuators (electric, pneumatic and hydraulic drives, positioners, solenoid valves and valves as well as their complete assembly) and their occurrence from the users' point of view. Occurrence 1 means essential for the development of diagnosis measures, Occurrence 4 means less required. In this context application-specific faults may not be understood as device failures. Fault conditions indicate deviations from the intended operating modes. The technical feasibility of a diagnosis method has not been taken into consideration in the list of faults/fault conditions. No statements are made here about the cost-value ratio of a specific diagnosis method. Tools and methods which can be used to draw conclusions about the condition of an actuator are listed here also albeit these tools and methods cannot be assigned to a certain fault. Prior to a diagnosis of faults in operating mode is the prevention of faults by a proper selection and dimensioning of the actuator suitable for the particular process. Depending on chosen type of actuator or chosen construction some of the listed faults don't arise. Moreover accurate installation and verification before and during the commissioning should obtain a top priority to avoid further fault conditions. For optimisation of the plant operating the feasibility of diagnosis is of importance also.