The increasing use of electronics in the automotive and avionic domain has lead to dramatic improvements with respect to functionality, safety, and cost. However, with this growth of electronics the likelihood of failures due to faults originating from electronic equipment also increases. In order to tackle prevalent diagnostic problems such as the reduction of the fault-not-found ratio, a maintenance-oriented fault model is needed that serves as the basis for the classification of experienced failures. In this paper we introduce such a maintenance-oriented fault model that establishes the conceptual foundation of the diagnostic services of the DECOS integrated architecture. The fault model takes the component-based nature of today's distributed embedded systems into account. According to this model each experienced failure is classified according to the field replaceable units of the system.