In specific circumstances, self-employed individuals can deduct auto loan interest on their federal income taxes. 

A self-employed individual may deduct on Schedule C interest paid on a loan to acquire a business vehicle even if the loan is consumer debt. This is so even if the standard mileage rate method is used because the standard rate does not include an allowance for interest to purchase the vehicle. If the vehicle is part for business and part personal, the interest must be allocated between the personal (non-deductible) part and the business part (IRC Sec 163).  In addition, the business portion of any taxes paid on the vehicle during the year is also deductible on Schedule C. (Rev Proc 2002-61, Sec. 5.04, 2002-39 IRB 616)