ah i see. if you owe more then what you can get for it, the left over would go on your new cars loan, or you would have to pay it outright.
if your buying a different car the rest of the money would go on the new cars loan. if your selling the car private party, you would have to take care of the loan
at the time of sale. you cant sell the car private party and not pay the amount due, it has to be paid at the time of sale at the lean holder.
if your wanting to trade your car in, then the rest of the loan left over would get tacked on to the new cars loan. if you owe 15 and they only give you 12k for it, 3k gets tacked onto
your new cars loan. hopefully your credit is very good, getting dealership to take a car with negative equity is kinda difficult.
your better off selling it private party and getting rid of that loan entirely.