if you purchased the vehicle and it was put into service in the same year as the $16K was earned, then your deduction for the vehicle is not the $4K but can be up to the full cost of the vehicle times the % of business use which is determined by business miles to total miles driven during the year. Turbotax can figure the deduction when you go through the questions about the vehicle.
on the other hand, if you are leasing the vehicle then the deduction would be the lease payments times business use. you may need to make an adjustment to the deductible lease payments - referred to as lease inclusion.
see iRS pub 463 starting on page 22
