This legislation proposes to amend Section 202(a)(2) of the Clean Air Act, specifically targeting tailpipe emissions regulations. Its core purpose is to ensure that any regulation proposed or prescribed on or after January 1, 2021, does not mandate the use of any specific technology in new motor vehicles. Furthermore, the bill prohibits these regulations from causing a limited availability of new motor vehicles based on their engine type. The Administrator of the Environmental Protection Agency is directed to promulgate necessary revisions to existing regulations within 24 months of the Act's enactment to conform with these new statutory requirements.