Conversion and Tampering Regulations
All vehicle and engine conversions must meet standards instituted by the U.S. Environmental Protection Agency (EPA), the National Highway Traffic Safety Administration (NHTSA), and state agencies like the California Air Resources Board (CARB).
This section provides information on:
Under the Clean Air Act, EPA has the authority to regulate vehicle emissions. Light-duty vehicles and medium- and heavy-duty engines from original equipment manufacturers (OEMs) must be certified to meet applicable emissions standards. Regulations are in place to ensure emissions do not increase as a result of changes made to a vehicle or engine, including a conversion. The Clean Air Act prohibits anyone from knowingly removing or rendering inoperative any device or design element installed on a certified vehicle or engine. These actions could be considered tampering, a violation that carries a significant fine.
EPA issued Enforcement Policy on Vehicle and Engine Tampering and Aftermarket Defeat Devices in 2020, superseding all previous EPA tampering guidance memorandums, to help clarify what qualifies as tampering of emissions monitoring devices to prevent air pollution. The requirements in 40 CFR 85 specify that if a conversion system is compliant with EPA or CARB regulations, the manufacturer is exempt from the tampering prohibition for that particular system. Emissions standards are fuel neutral, which means that the same emissions requirements must be met no matter which fuel or technology powers the engine or vehicle. Conversion systems must meet the same emissions standards that gasoline or diesel products do.
Refer to EPA's Vehicle and Engine Alternative Fuel Conversions website for the complete regulations, compliance procedures, and related information.
Manufacturers selling conversion systems for use in California must meet CARB requirements and obtain approval from CARB. EPA Certificates of Conformity or tampering exemptions are not required, nor will they take the place of CARB certification. For information on CARB procedures and requirements, visit the Certification of Alternative Fuel Retrofit Systems section of the CARB website.
Vehicle conversions that require the addition of heavy battery systems or additional fuel tanks that may alter a vehicle's center of gravity, payload capacity, or handling characteristics may need to be safety crash tested and certified to comply with Federal Motor Vehicle Safety Standards and other NHTSA regulations.
Demonstrating Compliance with EPA Regulations
All manufacturers must prove that a given vehicle or engine conversion complies with EPA regulations. Required demonstration and notification procedures differ according to the age of the converted vehicle or engine.
Vehicle owners and fleet managers interested in converting vehicles must work with the manufacturer or an authorized representative. Best practices dictate that the actual conversion work must be performed by a technician associated with the manufacturer that holds the relevant emissions-related certifications and tampering exemptions.
New and Relatively New Vehicles and Engines: This category includes conversions that take place within a calendar year and not more than one year after the original model year of the vehicle or engine. Conversion kit manufacturers must submit applications to the EPA, including test data, certification fees, and other information. Vehicles and engines in this category need an EPA or CARB Certificate of Conformity to qualify for an exemption from the EPA’s tampering prohibition. The EPA or CARB then issues a certificate to verify that the appropriate regulations and requirements have been met.
Certificate documentation indicates the following:
- The original test group, as determined and provided by the manufacturer
- The evaporative emissions family
- The state(s) in which the test group is certified
- The "car line," which includes the model and engine size
- The model year of the vehicles included in the test group
- The emissions standards met.
A certificate is valid for the specified certification year (referred to as the Model Year at the top of the certificate) and can be renewed. When they do expire, tampering exemptions remain in place as long as the conditions under which a certificate was issued do not change.
Intermediate Age Vehicles and Engines: This category includes conversions of vehicles or engines that are no longer "new or relatively new" but still fall within EPA's definition of useful life. Manufacturers of conversion systems within this category must demonstrate that the conversion meets emissions standards for the year in which the vehicle/engine was manufactured. The EPA does not issue certificates for this category but lists the compliant conversion kits. Annual renewal is not required to maintain a tampering exemption.
Vehicles and Engines Outside Their Full Useful Life: This category includes conversions of vehicles or engines that are outside EPA's definition of useful life. Manufacturers must submit information showing the system is technically sound. As with the intermediate age category, EPA does not issue certificates but will publicly list the compliant conversion systems as having satisfied the requirements. Annual renewal is not required to maintain a tampering exemption, as long as the conditions under which the exemption was granted do not change. Fleets should take note that some conversion kits are only certified for use on vehicles that are outside of useful life, and it is illegal to install these kits onto new or intermediate age vehicles.
See the Federal and State Incentives and Laws section to find incentives and other programs that could help offset conversion costs.