Immediate Sale

If the charity sells your car without modifying it or using it, your deduction is limited to the amount your car sells for instead of the fair market value.

Significant Intervening Use

If the charity uses your vehicle to further the mission of the charity, such as delivering meals, you can claim the fair market value of the car.

Donation to Needy Families

If the charity sells your car at a reduced price to a needy family to further the mission of the charity, you are allowed to claim the market value of the car. For example, if the charity's mission is to provide transportation to low-income families and it sells your $4,000 car to a needy family for $1,000, you can deduct $4,000. However, if the charity sold your donated $4,000 car at auction for the general public, and the winning bid was only $1,000, you would be able to deduct only $1,000.

Documentation

You must include a copy of the receipt you receive from the charity with your tax return. The charity has 30 days to provide you with this documentation, either from the date you turn over your car for the charity to use to further its mission, or from the date of the sale.

Filing

To claim the tax deduction for a donated car, you must itemize your deductions. You must also file your taxes using Form 1040 and attaching Schedule A. If your deduction is between $500 and $5,000, you must fill out Section A of Form 8283. If your deduction exceeds $5,000, you must fill out Section B of Form 8283.

Source:

Edmunds: Does Charity Car Donation Still Make Sense Under Tougher IRS Rules?

Bankrate: Donating a Vehicle to Charity

IRS: A Donor's Guide to Vehicle Donations