Auto loans are closed-end credit and the rule is that you may not state a simple rate without also stating (with equal prominence) the (properly calculated) APR. With no fees and an interest basis of 365/365, the simple rate and APR should differ only when you use the U.S. Rule to compute your interest and payment schedule, and then switch to the actuarial method for the APR. Unless the interest rate is sky high, this difference will only be a few basis points--never enough to worry about being out of tolerance.
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...gone fishing.