In the vehicle industry the electrical control units has a necessary diagnostic function. As the roles and functions of these units are flaring, the importance of the diagnostic functions growing, and became diversified, and nowadays its role is not only fault finding. For drawing up these abilities several standards can be found, which specify these in details, moreover application related parts became a part of the standards, to ensure the compatibility between units applying the same diagnostic standard. According to communication protocols it has benefits to break it off according to the ISO/OSI layers, making easier to define the roles and functions all of them. While reading the thesis, the UDS – Unified Diagnostic Services – diagnostic standard will be explained. According to the ISO/OSI model the application layer of the standard will be discussed in details, presenting the services and describing the opportunity of testing them. Beside this function, it is necessary to give the opportunity to help the processing of the results, these functions are essential for helping the development, because evaluating hundreds of thousand of test steps would make impossible difficulties for the developers of the control units. Using these results, special features will be described for getting more information about the functionality of the diagnostic services that will be tested. These requirements motivated that a graphical application would be necessary for these methods. The most important aspect of the planning was simplifying the evaluation of the results. For proving the benefits of the test software, all the configuration files will be created, and after these steps solving some issues related to the control unit was a possibility, and it connects to the subject of the thesis, because in the control unit an embedded implementation of the UDS standard can be found. For testing the diagnostic functions a database is necessary, where the functioning of these methods described in details. For interpreting the whole system the ODX – Open Diagnostic Data Exchange file was useful and essential, without this description the testing would not finish successfully.