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Vehicle and Engine Certification

Vehicle and Engine Alternative Fuel Conversions

On this page:

Overview of Conversions

Consumer Information

If you are interested in modifying your vehicle or purchasing a modified vehicle, see:
For general information, see:

Conversion systems modify vehicles and engines so that they can run on different fuels than the ones for which they were originally designed.

Any change to the manufacturer’s original vehicle or engine design is a potential violation of the Clean Air Act and can cause problems, including increased emissions.
Therefore, EPA has established protocols through which conversion manufacturers can demonstrate that:
  • Emission controls in the converted vehicle or engine will continue to function properly; and
  • Pollution will not increase as a result of conversion.
These protocols are conveyed through the following rules and guidance:

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Related Guidance Letters

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How to Submit Information to EPA to Demonstrate Compliance

EPA's Final Rule for Clean Alternative Fuel Vehicle and Engine Conversions spells out processes through which conversion manufacturers may demonstrate compliance with vehicle and engine emissions requirements. The processes differ depending on the age of the vehicle or engine to be converted.

There are three age-based demonstration categories:
  • Conversion systems to be used on new and relatively new vehicles/engines;
  • Conversion systems to be used on intermediate-age vehicles/engines; and
  • Conversion systems to be used on outside useful life vehicles/engines.

The following information summarizes the requirements.  Regulated parties should always refer to the regulations for compliance purposes.

Conversion Systems to be used on New and Relatively New Vehicles

The compliance demonstration for conversion systems intended for use on new vehicles and engines is a certification process similar to the original engine manufacturer certification process. Use the applicable link below.

Conversion Systems to be used on Intermediate Age and Outside Useful Life Vehicles

The compliance demonstration for conversion systems intended for use on intermediate age and outside useful life vehicles and engines is described in regulations and guidance. Please follow the link provided below for information about how to submit the applicable templates and information:

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Lists of EPA-Compliant Conversion Systems

Once a manufacturer has demonstrated compliance, the conversion system will appear on the applicable list:

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