Aftermarket, Performance and Add-On Parts Regulations

This page last reviewed March 10, 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 aftermarket fuel converters are different than U.S. EPA’s requirements.  California’s requirements remain the same as those adopted in 1995 (specified in the procedures below) and apply to all vehicles, regardless of their age.  Manufacturers wishing to sell and install their alternative fuel conversion systems in California must first obtain certification from ARB.

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 the Help Line at (800) 242-4450.

What's New:


ARB is currently considering amendments to the Alternative Fuel Conversion Certification Procedures for new and in-use vehicles and engines.

preload