If you donate a qualified vehicle to a qualified organization you must send the IRS form 1098-C.
Per IRS Publication 17 Your Federal Income Tax (For Individuals), page 167:
Cars, boats, and airplanes. The following rules apply to any donation of a qualified vehicle.
A qualified vehicle is:
Form 1098-C. You must attach to your return Copy B of the Form 1098-C, Contributions of Motor Vehicles, Boats, and Airplanes, (or other statement containing the same information as Form 1098-C) you received from the organization. The Form 1098-C (or other statement) will show the gross proceeds from the sale of the vehicle.
If you e-file your return, you must:
If you don't attach Form 1098-C (or other statement), you can't deduct your contribution.
You must get Form 1098-C (or other statement) within 30 days of the sale of the vehicle. But if exception 1 or 2 (described later) applies, you must get Form 1098-C (or other statement) within 30 days of your donation.
Please see IRS Publication 17 for more information.
If you need to submit supporting documentation and would like to electronically file your return, you must mail the documents to the IRS along with Form 8453.
First, enter the information from Form 1098-C in the TaxAct program:
If you provide information for the contribution of a vehicle, you will be prompted to print Form 8453 in the filing steps. Attach the supporting documentation to Form 8453 and mail this information to the IRS, as directed in the Federal Electronic Filing Instructions (which can be viewed or printed later in the e-file screens).
Form 8453 and the required forms or supporting documents must be mailed to the IRS within three business days after receiving acknowledgement that your return was accepted. An electronically transmitted return will not be considered complete until a Form 8453 is received by the IRS.