About using your personal car in Germany:
If you have lived abroad at least twelve months before your stay you may bring your car free of customs duties if you have used it abroad for at least six months. For stays of up to twelve months, a foreign car may continue to be registered in your home country. For longer stays or cars purchased in Germany, you will have to register your car at the Motor Vehicle Registration Office (`Kraftfahrzeug-Zulassungsstelle´) at your place of residence.
Quelle: Karlsruhe Institute of Technology.