Abstract: A self diagnostic system is integrated into an application program for controlling a machine or process. The application program is comprised of various logical segments that have to be solved by a logic solving engine. The diagnostic program will annunciate an event when the application program cannot execute a desired response by monitoring certain preselected and marked segments of the application program and allocating memory to save the result. When an abnormal occurrence in these segments results in the desired event not occurring, the diagnostic system will determine what part of the logic expression controlling the event could not be completed. This information will be saved and used for annunciating the reason for the desired event not happening. The diagnostic system includes a special control module that is added to the application program.