In the current article, the reasons are find out why computer diagnostics of technical objects by traditional algorithms does not work correctly. The new approach is offered on how to form a diagnosing algorithm by using the theory of pattern recognition. The recognition models as part of diagnosing algorithm may be built on the base of analytic forms. This results in efficiency algorithms, especially in test procedures. Incorrect mathematical forms are avoided in calculation operations. This allows getting able-bodied computer diagnosing programs for technical objects with checking and diagnosing systems, which operate automatically.