Ethanol Flexible Fuel Vehicle Conversions

Updated July 29, 2011

Vehicle manufacturers currently offer E85 (85% ethanol, 15% gasoline)-compatible flexible fuel vehicles (FFVs) in a wide variety of makes and models at little or no extra cost. In spite of the availability of new and used FFVs, many consumers are curious about the prospects for converting their existing gasoline vehicles to operate on E85.


The U.S. Environmental Protection Agency (EPA) implements regulations under the Clean Air Act that require vehicles to be certified as compliant with emissions requirements (see the Code of Federal Regulations (CFR), Title 40, Parts 85-88). Certification is granted to the manufacturer for specific vehicle configurations operating on specific fuels according to an established test protocol. Installing or modifying a fuel system to allow a vehicle to operate on a fuel or technology other than that for which it was originally certified may be considered tampering—a violation of federal regulations that carries a significant fine.

EPA oversees the process by which manufacturers of conversion systems can obtain a Certificate of Conformity or an exemption from the federal tampering prohibition, depending on the age of the converted vehicle. This process certifies the converted vehicle, not the conversion system by itself. EPA testing procedures for FFV conversions ensure that the converted vehicle meets emissions standards and all vehicle components and materials will be compatible with E85 for as long as the vehicle remains on the road.

The specific design changes required for FFV conversions vary among original equipment manufacturers (OEMs), model years, and vehicle test groups. In addition to replacing metallic components, elastomers, and polymers with materials that are compatible with ethanol, key components in the fuel supply system may need to be changed to accommodate the need for greater fuel delivery when using E85.

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Regulatory Requirements

Regulations requiring aftermarket fuel conversion manufacturers to certify their conversions are found in 40 CFR Parts 85 and 86. FFV conversion systems must be certified by EPA or granted a federal tampering exemption, depending on the age of the vehicle. Conversion systems are not considered to be a type of "device," as has been suggested by some manufacturers, which might otherwise allow conversion manufacturers to sell their systems without obtaining EPA certificates or tampering exemptions. This situation is sometimes the case with devices such as high-performance air filters, free-flow mufflers and exhaust systems, and some other aftermarket accessories.

Certification Process Overview

Certification of fuel conversions closely follows the process OEMs use when certifying new model year vehicles. For new vehicles, EPA issues certificates for specific vehicle groupings, called an engine family or test group. A test group, designated by the OEM, contains vehicles with common design elements (such as the number of cylinders or a specific engine and transmission configuration) and similar emission components (such as a similar size catalyst and precious metal loading). There are many test groups for a particular OEM for a given model year, and there are often different test groups for what might appear to be the same kind of vehicle. For example, a pickup truck may be available with either two-wheel or four-wheel drive or with different engine and transmission combinations, each of which might require a separate series of tests and individual certificates or tampering exemptions.

The process for new FFV conversions takes a similar approach. Each test group of a specific vehicle type with a specific conversion system is tested and considered for certification. The tests ensure that the converted vehicle meets emissions standards when operated on any blend of ethanol and gasoline, from 0% ethanol to 85% ethanol (E85), for the full useful life of the vehicle. It also ensures that the OEM's gasoline vehicle components and materials will be compatible with E85 throughout the life of the vehicle.

EPA revised the conversion regulations found in 40 CFR Parts 85 and 86, effective April 8, 2011, to establish three age-based categories for compliance demonstration and notification. For converted vehicles "new or relatively new," as defined by EPA, the certification process is summarized above. Older vehicles require exemptions from EPA.s tampering prohibitions, and EPA does not issue a certificate. The table below summarizes the requirements; see the EPA Alternative Fuel Conversion website for more information.

Summary of EPA Age-Based Demonstration and Notification Requirements

Category Applicability Demonstration Notification Certificate Issued?
New and Relatively New Model year greater than or equal to current calendar year minus one Testing Certification application Yes
Intermediate Age Model year greater than or equal to current calendar year minus two and within useful life Testing Electronic submission No
Outside Useful Life Exceeds useful life Technical justification and limited testing Electronic submission No

There is no "one size fits all" category or universal EPA certificate or tampering exemption for a conversion system that would allow it to be legally installed on any vehicle type or engine configuration. How the specific fuel and emissions control systems work together determines compliance with EPA emissions standards for a particular vehicle.

If a company wants to sell FFV conversion systems in California, similar procedures must be followed to obtain approval from the California Air Resources Board (CARB).

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Emissions Standards

Emissions standards are fuel neutral, which means that the same emissions requirements apply no matter the fuel type. Therefore, to prove compliance with emissions standards, converted vehicles must demonstrate they meet the standards when using the alternative fuel. For FFV conversions, manufacturer must prove emissions compliance with exhaust standards when vehicles are operating on gasoline as well as E85.

On-board Diagnostics

A vehicle's on-board diagnostic (OBD) system performs constant checks to ensure that all emissions-related components operate correctly. The OBD system notifies drivers of any issues or problems by illuminating a malfunction indicator light on the dashboard (sometimes called the check-engine light). Meeting EPA OBD requirements is a fundamental part of the certification process, and these requirements are described in detail in EPA's conversion regulations.

Obtaining an OBD approval letter from EPA is just one step in the overall certification process and is not by itself an approval from EPA for the sale of conversion systems. The approval letter only documents that EPA has reviewed the operation of the fuel-converted vehicle's OBD system, including any necessary supporting data, and finds that it meets EPA's OBD regulatory requirements.

Conversions sold in California must receive an OBD approval from CARB.

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Technology Information:

EPA Guidance:

CARB Guidance:

Federal Regulations: