When you donate a car you may deduct the fair market value when filing your taxes, this may be different than the Kelly Blue Book Value, as vehicle worth varies depending on the type of re-sale marketplace.
The actual amount you are able to deduct is dependent on what the charity does with the donated vehicle. Once your charity sells the vehicle, your deduction is limited to the gross proceeds the charity receives from selling the vehicle. If that amount is less than $500, you may be able to deduct the fair market value up to $500.
Sample Scenario from Cars.com:
On April 1, 2013, you donated your car to the local food bank. When you donated the car, you had determined that the fair market value was $4,300. On April 15, 2013, the charity sold your car (to someone other than a needy individual), without any significant intervening use or material improvement, and received gross proceeds of $3,700. Your deduction may not exceed $3,700.