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Vehicle and Engine Certification

Information for Consumers about Alternative Fuel Conversions

Manufacturer Information

If you are a manufacturer interested in modifying vehicles, see:

The benefits of conversion will vary depending on your situation and your objectives. Please educate yourself thoroughly before altering your vehicle or engine to run on an alternative fuel or before buying a converted vehicle or engine. Here are some factors to be aware of if you are considering fuel conversion.

Environmental Impact and Benefits

Some fuels have a reputation of being inherently “clean” but in today’s vehicles and engines, it is not the fuel alone but rather the sophisticated integration of engine, fueling, exhaust and evaporative emission control system designs that determine how clean a vehicle will be. Fuel conversion systems must retain a sophisticated and integrated design logic and functionality in order for emissions to remain low. Conversion to alternative fuels can be environmentally beneficial, but conversion does not necessarily reduce pollution. Manufacturers of EPA-compliant fuel conversion systems must demonstrate that the converted vehicle or engine meets the same standards as the original vehicle or engine, or, for older vehicles and engines, that emissions do not increase as a result of conversion.

Cost and Range

The cost of running a vehicle on an alternative fuel will depend on fuel price and on how far you can travel on each unit of fuel. The amount of fuel you need will depend on the fuel’s energy density, and on whether the converted vehicle is optimized to take advantage of the alternative fuel characteristics. Operating costs may be either higher or lower for a conversion than for the original configuration. Alternative fuel prices tend to fluctuate considerably more from region to region than gasoline and diesel fuel prices. The U.S. Department of Energy maintains an up-to-date report on alternative fuel prices around the country at

Electricity, gaseous fuels, and alcohol fuels are generally less energy dense than gasoline and diesel fuel. Depending on how much alternative fuel you can store onboard, you may not be able to travel as many miles on a “fill-up” and may need to refuel more frequently.

Fuel Availability

As with fuel price, alternative fuel availability varies greatly from region to region. The U.S. Department of Energy maintains an alternative fueling station locator.


Consumers considering conversion should investigate warranty implications in advance. Warranty liability for certain failed components in a converted vehicle or engine may transfer from the original equipment manufacturer to the conversion manufacturer. Generally, the conversion manufacturer maintains liability for problems that occur as a result of conversion, while the original manufacturer retains responsibility for the performance of any covered parts or systems that retain their original function following conversion and are unaffected by the conversion. Consumers should be aware that liability in a given conversion situation may not be clear, creating potential for confusion and even for dispute over which manufacturer is responsible for repair.