Because of environmentally based legislative regulations, diagnosis of automotive engines has become increasingly important. In the design of diagnosis systems, it is important to strive for optimum performance and at the same time, minimize the amount of engineering work required. Therefore, it is desirable to have a highly automated design procedure, in which diagnosis performance is optimized. It is discussed how a diagnosis system for the air-intake system of an SI-engine, can be constructed with the help of automated tools. In particular the problem of residual and threshold selection is addressed. For this a fully automatic algorithm is proposed and it is experimentally shown that the algorithm successfully manage to generate a well functioning diagnosis system.