Just read this online:
Car manufacturers will let you know upfront what the maximum dollar value of your tax credit will be. Your hybrid tax credit may be reduced by various limitations.
Under guidance released by the IRS, car manufacturers can issue you a written certification specifying the dollar amount of your hybrid tax credit. The IRS mandates that the manufacturer's certification must have the following sixteen elements:
Name, address, and tax identification number of the manufacturer,
Make, model, model year, and other vehicle identification information,
A statement that the vehicle was made by the manufacturer,
The type of credit for which the vehicle qualifies,
The dollar amount of the tax credit (showing all computations),
The gross vehicle weight rating of the vehicle,
The vehicle inertia weight class of the vehicle,
The city fuel economy of the vehicle,
Statement that the vehicle complies with the provisions of the Clean Air Act,
Copy of the certificate that the vehicle meets emission standards under the Clean Air Act,
Statement that the vehicle complies with state air quality control laws.
Statement that the vehicle complies with certain motor vehicle safety provisions,
Statement that the vehicle uses hybrid technology (both internal combustion and a rechargeable energy storage system),
Statement that the vehicle meets or exceeds California low emissions vehicle standards,
Evidence that the vehicle does not exceed maximum power standards.
Perjury statement as follows: "Under penalties of perjury, I declare that I have examined this certification, including accompanying documents, and to the best of my knowledge and belief, the facts presented in support of this certification are true, correct, and complete."
I suspect this will be one long tax document. You should keep this tax certification for at least four years.