Aftermarket, Performance and Add-On Parts Regulations

This page last reviewed June 26, 2014

Certification of Alternative Fuel Retrofit Systems
California regulations prohibit the conversion of emission-controlled vehicles with retrofit systems to operate on an alternative fuel, such as natural gas, propane, or ethanol, in lieu of the original gasoline or diesel fuel unless the retrofit systems have been evaluated and certified by the Air Resources Board (ARB). The certification of an alternative fuel retrofit system must be obtained by its manufacturer. Certification is issued by ARB once the manufacturer demonstrates compliance with the emission, warranty, and durability requirements. A manufacturer is defined as a person who manufactures or assembles an alternative fuel retrofit system for sale in California. An individual who wishes to convert a vehicle for personal use does not fall under this definition and cannot certify a retrofit system in California.

The United States Environmental Protection Agency (U.S. EPA) recently streamlined its rules for alternative fuel converters using a 3-tier approach based on vehicle age/useful life (published April 8, 2011).  This has prompted numerous inquiries regarding their applicability in California.  As clarified in U.S. EPA guidance letter CISD-10-24 (Q&A # 9), California’s requirements for alternative fuel converters are different than U.S. EPA’s requirements.  Revisions to California’s Alternative Fuel Conversion regulation and test procedures were approved by the Board on September 26, 2013.  2003 model year and earlier vehicles were not affected by these changes.  The revisions provided for streamlining of the conversion approval process for 2004 Model year and later vehicles/engines.  Small volume manufacturers were given some additional relief which sunsets after the 2017 model year.  ARB will allow use of the new regulations on a conditional basis until they are officially adopted.  Details and status of this regulatory item may be followed at the Alternative Fuel Conversion webpage.

Individuals interested in converting their vehicles to operate on an alternative fuel must ensure that the alternative fuel retrofit systems used for their vehicles have been certified by ARB. The list of certified retrofit systems for various vehicle makes and models are available online. You may view a list of certified retrofit systems for 1994 and newer model year vehicles (PDF - 125K), or for 1993 and older vehicles (PDF - 1.50MB).

View the procedures for certifying retrofit systems designed to convert vehicles to operate on natural gas, propane, or ethanol fuel at (PDF - 1.95MB). To obtain information on certification requirements for retrofit systems using other alternative fuels such as hydrogen, plug-in hybrids, biodiesel, please contact Antonio Martino, Manager Aftermarket Parts Section at (626) 575-6848 or

What's New:

The Board has approved amendments to the Alternative Fuel Conversion Certification Procedures for 2004 and newer and in-use vehicles and engines.