Abstract In the scientific literature, it is generally assumed that models can be completely established before the diagnosis analysis. However, in the actual maintenance problems, such models appear difficult to be reached in one step. It is indeed difficult to formalize a whole complex system. Usually, understanding, modelling and diagnosis are interactive processes where systems are partially depicted and some parts are refined step by step. Therefore, a diagnosis analysis that manages t abstraction levels and partly modelled components would be relevant to actual needs. This paper proposes a diagnosis tool managing different modelling ion levels and partly depicted systems.