A methodology for improving quality and reducing life cycle costs of mechanical systems is described. The principle concept is that a system can be designed, in the conceptual stages, to be easier to diagnose for failures. To perform this, functional decomposition and form to function mapping are utilized both as a model of design and to demonstrate the relation of diagnosis to design. Design guidelines from other disciplines of engineering and concurrent engineering principles are applied to enhance the concept. The affects of the different elements of concurrent engineering on each other are explored. Of the elements of concurrent engineering, design for manufacturability affects the others the greatest. Design for manufacturability principles impact the size of field replaceable units and can improve the ease of failure diagnosis of a system. For a hypothetical case, form to function mapping that would create a difficult to diagnose system is redesigned to reduce the difficulty of failure diagnosis. Further, three diagnosability metrics are developed and four hypothetical conceptual designs are evaluated for diagnosability and compared The area of design for diagnosis offers promise in improving system quality and reducing life cycle cost; research is continuing to refine and integrate the procedures with other components of the concurrent engineering design process.