Abstract: A diagnostic device for at least one pneumatic valve actuator arrangement comprises a pressure sensor, a volumetric flow sensor, a control means for producing control signals for the valve actuator arrangement and position sensors for detecting the position of at least one moving actuator member. The diagnostic device also includes a first diagnostic module for leak detection, a second diagnostic module for the detection of a choking effect in pneumatic supply and venting lines and at least one third diagnostic module for the detection of load and friction changes in the case of the moving actuator member and/or of valve switching faults, switching means being provided for deactivating the at least one third diagnostic module in the case of the detection of a fault by the first and/or second diagnostic module.