This is a very good question.
You will be in the auto expenses form. You can see where you can enter interest expense. There are 2 date entry. One for when the payments began during the year (01/01/2017) and the other date for when the interest payments ended. Here you enter the day you paid off the loan.
The amount you paid off does not go anywhere on the return. Only the interest is a deductible expense.
