EPA and Conversions

In June 1974 the U.S. Environmental Protection Agency (EPA) issued Mobile Source Enforcement Memorandum 1A (Memo 1A). The original purpose of Memo 1A was to enforce the tampering prohibitions under Section 203(a)(3) of the Clean Air Act with respect to maintenance and use of aftermarket parts. Memo 1A and its subsequent revisions also outline procedures for converting vehicles to operate on alternative fuels while still complying with the Clean Air Act's tampering prohibitions and ensuring that emissions are not degraded through the conversion process. Below is a timeline and information about subsequent revisions to Memo 1A.

In the mid 1990s, testing determined that some vehicles that had been converted to operate on alternative fuels, specifically propane and natural gas, produced emissions that were worse than those of baseline gasoline vehicles. EPA issued an Addendum to Memorandum 1A in September 1997, requiring more stringent emissions testing for alternative fuel vehicle (AFV) conversions. The addendum specified three options through which a manufacturer can demonstrate that it has a "reasonable basis" to believe that its aftermarket part, vehicle add-on, or alteration to the vehicle would not adversely affect vehicle emissions performance. In order to promote initial growth of the alternative fuels industry, Option 3 outlined less stringent requirements than obtaining a Federal Certificate of Conformity required under Option 1 or the California Air Resources Board retrofit system certification required under Option 2.

Due to comments received from industry, and concerns about the testing process and timeline, EPA issued a Revision to the Addendum to Memo 1A in June 1998. The revision clarified certain points and extended the timeline for performing conversions according to the guidelines specified under Option 3 to June 30, 2000. Additional concerns from the small alternative fuels industry related to the costs of "full certification" under Options 1 and 2 led to another extension of Option 3, which was issued in May 2000 and extended the deadline for performing conversions without full certification to December 31, 2001. Finally, on January 24, 2002, EPA extended Option 3 through March 31, 2002 in order to allow time for a new set of certification procedures for fuels converters to be fully developed by EPA.

Following these three extensions, Option 3 of the addendum to Memo 1A officially expired on March 31, 2002. Option 3 had permitted the use of alternative fuel conversion systems or "kits," which were designed for specific engine families, provided that the aftermarket conversion company performed satisfactory emission testing demonstrating that the converted vehicles conformed with EPA emissions standards. Options 1 and 2 remain in effect, and EPA now certifies converted vehicles, rather than conversion systems or "kits." For more information about current conversion certification procedures, please see Conversions 101.

For more information about Memorandum 1A and mobile source emissions standards, please visit the following Web pages:

• Light-Duty Vehicle and Engine Emission Certification
• Vehicle Standards and Regulations
• A Guide to the Emissions Certification Procedures for Alternative Fuel Aftermarket Conversions (PDF 2 MB) Download Acrobat Reader. (This document should be referred to for historical and background purposes only.)
• Mobile Source Enforcement Memorandum No. 1A: Interim Tampering Enforcement Policy (PDF 292 KB)
• Addendum to Mobile Source Enforcement Memorandum 1A (PDF 32 KB)
• Revision to Addendum to Mobile Source Enforcement Memorandum 1A (PDF 380 KB)