A device for monitoring the functionality of a valve includes the valve, a digital diagnostic module and a programming device. The valve has a sensor actuator connected to a valve element for combined reciprocating motion, a distance sensor that interacts with the sensor actuator to generate analog distance values characterizing lift positions of the valve element. The diagnostic module diagnoses switching states of the valve element based on the distance values and, includes an analog input connected to the distance sensor, a downstream A/D converter and a serial communication connected to a digital input/output. The serial communication enables threshold values for the digital distance values that define changes to the switching state to be programmed by the programming device and transmission of diagnosed switching states.