It depends on the lender...
The answer isn't that elementary. Regardless of your credit, you can get approved for a car. It's a matter of using the right lender that fits your credit situation. You can get approved based on your income through special finance companies that offer their services online. there's real & legitimate lenders online that cater to helping people of all credit scores.
there's lenders that specialize in working with people that have prime, lovely, sub-prime, bad & poor credit. Finding the right lender is all that you need to get approved. there is no direct answer to the maximum credit score for an auto loan. All lenders are different.
Fortunately, if you have bad credit, you can get approved for a new or used car & your payments are based on your monthly income. It's elementary to obtain a car loan if you have a low credit score & getting approved with lenders that operate online is much faster than using a local bank, credit union or car dealership.
Believe it or not, new cars are as easy to get if you have bad credit. It depends on the make, model & the amount financed. If you can get approved easily for a $18,000.00 used car, it's even less difficult to get approved for an $18,000.00 new car. The maximum credit score to get approved through special finance online is 480.