if this is the first year that you have claimed the vehicle, you enter "0". If, however, you have claimed the vehicle in the past, you must enter the amounts you have claimed for depreciation in the past. That amount will be on your past tax forms (if you used TurboTax in the past, it should be automatically transferred). It could be that you have never declared depreciation despite using the vehicle over more than the past year, in which case you enter "0". In future, Turbotax will automatically enter the total claimed past depreciaition.
