Here is a post that I found that sounded like it would be helpful to you:
Question: In filling out form 2106 the system keeps asking me when I sold my vehicle. I didn't sell the vehicle, I have corrected this is my deductions section multiple times and it still wants to know when I sold the vehicle. Please help!
Reply: I ran into this exact problem as well. What i did was enter the last day of the year..the description of that section reads so as to lead me to believe that it is when you sold OR stopped using the vehicle...so to me that meant that I stopped using it for business during this tax year as of the last day of the year.