Advanced passenger car control is based on multiple electronic control units (ECUs), performing complex control algorithms and diagnostic functions for the different power train components like combustion engine, automatic transmission, brakes or chassis. For research and development the engineers need tools to test and verify either the reliability of new control strategies implemented in the ECUs or the interaction of different ECUs in a car. These tests should be done to the highest extent in the laboratory to reduce costs and risks which are involved in test stands or experimental cars. Therefore the optimal solution is the operation of the ECUs in a real-time closed loop environment. In this paper a real-time simulator, called CARTS® (Computer Aided Real-Time Test System) (figure1), is presented which is adaptable by a modular structure in hard- and software and a scaleable computing power to various ECUs or ECU networks, to various user demands, and to different simulation models. The paper gives a survey of the modelling methods, which CARTS offers and the requirements regarding hard- and software due to the real-time conditions.