TurboTax is not set up to report the sale of an asset (including a vehicle) that has varied in business percentage from year to year.
Did you purchase the vehicle in 2013 (when you started using for business)? If so, at first glance you have a LOSS, not a gain. However, because you sold it to a "related party", the loss is not allowed.
Because you don't have a gain or a deductible loss, I would just tell TurboTax that you converted it to personal use, which will get it off your tax return and property give you no gain or deductible loss.
