This document amends the U.S. Customs and Border Protection (CBP) regulations relating to the importation into the United States of certain vehicles and engines under the Clean Air Act (CAA) in order to harmonize the documentation requirements applicable to different classes of vehicles and engines that are subject to the CAA's emission standards. This document further amends the regulations to permit importers to file the required U.S. Environmental Protection Agency (EPA) Declaration Forms with CBP electronically, and amends non- substantive provisions to update regulatory citations and delete obsolete provisions.