An employer can make an employee, whether hourly, salaried, or commission only, pay costs, such as the maintenance expense (or insurance, or gasoline, etc.) of company vehicles. The law does not require either the company or you to pay this--it depends on the terms of your employent. If the employer wants you to have to pay this cost, you have to, the same way that if you travel for business, the company can make you pay your own airfare, hotel, etc. and not reimburse you.