Using quantitative models of simple mechanisms as an example domain, we show how the basic principles of consistency-based diagnosis can be implemented using description logics with expressive concrete domains. In addition, description logics provide the inference services necessary to organize and validate model libraries, an aspect that is neglected in consistency-based diagnosis until now. 1 Description Logics for Diagnosis Consistency-based diagnosis1 [7; 10] is a method for the diagnosis of technical devices based on descriptions of the correct and faulty behavior of components. Therefore, for representing, simulating and diagnosing the simple bike drive train in Fig.1 at least the following knowledge must be represented within such a system: