Automotive sub-systems, from security and energy, to comfort and entertainment, include several examples of entanglement between electronics andmechanics (H. Casier & Appeltans, 1998). Their correct modeling is of key importance during the design cycle, and, from conception to test, real critical conditions due to mechanic, thermal and electromagnetic stress sources must be taken into account. Typical design and test methodologies are both electronic and electro-thermo-mechanical, but they focus on a single fault source at a time. Moreover in most of the cases they are applied late in the design cycle. Accurately emulating a multi-disciplinary system during both design and test phases is of great importance when reliability is the first concern as in the automotive scenario case. The methodology tackled in this chapter, based on the VHDL-AMS language, can be applied both during design and performance or fault analysis and allows to focus on electronic devices internal parameters at a detailed level, and, meanwhile, to evaluate the influence of other electronics devices in the car system, the electro-mechanics of the vehicle and the static and dynamic usage conditions. One of the language/simulator used by system engineers in this field is Matlab/Simulink (Friedman, 2005) which allows modeling both electronic and mechanical systems at a very high hierarchical level, thus allowing to understand relations between the two fields from a system perspective. Problems arise when designers need to accurately model both electronic and mechanical devices. VHDL-AMS (1076.1, 1999) is a superset of VHDL, thus not only digital constructs are supported but electrical quantities, differential equations and algebraic constraints can be modeled as well. The effect is the possibility to describe mixed-technology systems, ranging from mechanics to optics, from thermodynamics to chemistry without the need to change simulation tool. Its suitability for automotive electro-mechanical systems modeling results in the effectiveness in capturing the impacts of electronic blocks at the system level, and, on the other hand, in achieving a good understanding of impact mechanics on electronic design choices as well. Multi-resolution is a further relevant VHDL-AMS characteristic: It allows to describe different blocks in the system using different levels of abstraction, depending on the focus needed for different devices. In the automotive context this is a great improvement as it implies, for example, that critical electronic blocks can be accurately described, while the thermo-mechanical car environment can be only approximately represented. This favours a lightweight simulation in terms of required CPU time. A further important achievement consists in the possibility to capture the effects of electronic details at the system level, and, on 27