This paper deals with the modelling and the validation of multiple networked embedded computer systems supporting in-vehicle applications. In this context, we developed a modular modelling and simulation technique. This approach allowed the development of reusable component models with clearly defined interfaces. The building of a whole application model is then obtained by integration of these components, so that model construction and result analysis are made easy. In fact, thanks to the formal definition of components, interfaces and composition rules, this step is automatically achieved. In the context of CAROSSE project , we implemented this methodology in the Carosse-Perf tool. Herein, we will detail the methodology together with its modelling principles and the resulting definition of basic components and interfaces. Finally, we will apply it to a case study withdrawn from a PSA Peugeot-Citroën application.r the text in that file's own buffer.