Good question! While there is no universal minimum score, lenders have their own standards below which they will not approve an auto loan.
Improving your credit score can save you money on a car loan. At the time of this writing, a borrower with a good credit score (700-749) will likely be approved for a rate around 5.3%. Someone with poor credit (450-649) will pay interest over 17% if they can get approved.
If you want to think of the minimum as 450, you can, but you will need to search far and wide for a lender to accept that score and provide loan terms that you can reasonably afford.
If you have poor credit, your best bet is to hold off on borrowing money and do all you can to get your credit score up.