Virginia does not have a crime called "grand theft auto." Virginia law generally refers to stealing offenses as larceny - and then separates larceny into misdemeanor larceny (petit larceny) and felony larceny (grand larceny) depending on the value of the property stolen. The act of stealing a car generally falls into the Grand Larceny category because of the value of the car stolen.
If you are convicted of the felony offense of Grand Larceny, you may be incarcerated for up to twenty (20) years.
However, even in the limited information you provided, I see possible avenues of defense which suggest that you may not be guilty of any crime at all. Of course, in order to fully pursue these matters you are going to need the assistance of an experienced Virginia Criminal Defense Lawyer.
DISCLAIMER: This answer is provided as general information and is not to be considered legal advice, nor does it constitute the creation of an attorney-client relationship.
T. Kevin Wilson, Esq.
The Wilson Law Firm
DUI, Criminal & Traffic Defense...When Results Matter
9300 Grant Avenue, Suite 301
Manassas, Virginia 20110