Answer by Wray Rives:
An S corp owner can purchase an auto personally and if you use the vehicle more than 50% for business, then you can take a Section 179 deduction; however, you will probably receive a larger deduction by having the corporation purchase the vehicle.
If you purchase the vehicle personally, then the Sec 179 deduction will be an un-reimbursed employee business expense subject to 2% of AGI limitation. If the corporation purchases the auto, then you don't have the miscellaneous itemized deduction limit to deal with.
However, having a corporation buy a vehicle may not always be the best financial choice, because interest and insurance rates are often more expensive than when a vehicle is purchased personally. You also still have to document the business usage by tracking mileage and keep a record of actual expenses.
If you are going to purchase the vehicle personally, then you may be better to have the corporation provide you a mileage reimbursement under an accountable plan for the business miles, rather than try to deduct depreciation and actual expenses. The mileage reimbursement is a tax deduction for the corporation which reduces your income on your K1 from the corporation and is not income for you personally.