There is described a method for monitoring the functionality of an automation system of a plant comprising at least one main processor, parts of the plant being monitored and controlled using a user software, which is constructed of a number of program modules and which is run on the main processor. A co-processor is assigned to the main processor, and a message is transmitted from the main processor to the co-processor. When received, this message is used by the co-processor to start a monitoring time. When a subsequent message is received, this monitoring time is reset before said monitoring time has elapsed, otherwise a fault is identified once the monitoring time has elapsed.