Have you downloaded a trial version of System Modeler?

https://www.wolfram.com/system-modeler/trial/

If you have a concrete question about system modeler while trying to use it, contact them or the sales department and they'll be happy to answer your question. They usually can't answer open ended questions or requests for programming help, but if you have specific questions, they are usually able to help people using the trial version.

Thank you very much for your help. It is much appreciated.

I would also like to know how Models built with SystemModeler can be used and examined in Mathematica. Thank you.

What is a full body car model? Is that a technical term or are you just looking for a very complete mathematical model of a car?

What kind of Mathematical model?

SystemModeler is more often used by the industry for modeling automotive parts: http://www.wolfram.com/system-modeler/industry-examples/automotive-transportation/

Models built with SystemModeler can be used and examined in Mathematica.