Auto loan uses auto-enhanced FICO score most of the time. This FICO score is different than the score you get from myFICO or from credit card application. It weighs more on existing auto loan history and less on everything else. If you don't have auto loan history before and a so-so 650 FICO score you may need a co-signer.
Usually it is better to get an auto loan outside of dealership first. If approved lender will give you a check which you then use it to pay for a car like you would for cash. Amount written on the check is your loan amount.