| Presented By Rav Chaim Weg
Answer: It is clear from the Gemara and Shulchan Aruch that it is assur to benefit from stolen goods. Thus, one may not enter a house that was stolen or use an animal for work in the fields that was stolen. In fact, the sefer Toldos Chafetz Chaim comments that the Chafetz Chaim never walked on the wooden boards placed on top of the snow and mud in the unpaved streets of Radin in the winter because he was afraid that they may have been stolen.
However, it seems from the details of this case that the car was not actually stolen. Rather, the price was paid in full to the car dealer by the bank, which financed the deal, and the owner of the car is now obligated to repay the money to the bank. If he does not do so and cheats the bank from the money he owes, he may be stealing from the bank and violate the prohibition of Lo Sa'ashok (withholding money from someone else who is entitled to it). But the car is not considered stolen, and no issur hana'ah would exist forbidding anyone from benefiting from the car.
Even if the one who purchased the car received a loan from the car dealer himself in order to finance the sale, not returning the loan would still not render the car to be stolen goods, since nowadays car dealers generally outsource loans and financing. Thus, whatever loan the car dealer extends to the buyer likely comes from a bank or similar institution, which has already paid the dealer in full. Here too, the buyer's transgression of not returning the money does not render the car stolen. | 
