UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY 

2565 PLYMOUTH ROAD 

ANN ARBOR, MICHIGAN 48105-2498

 OFFICE OF 

AIR AND RADIATION 

 CISD-09-14 (LD-AFC, LDV, LDT, HDV, HDE) 

June 20, 2009 

SUBJECT: Updated Certification Guidance for Alternative Fuel Converters 

Dear Manufacturer: 

This guidance letter, with its Attachment, supplements the guidance contained in EPA 

Dear Manufacturer Letter CISD-06-02, dated February 3, 2006, which may be viewed at: 

http://www.epa.gov/otaq/cert/dearmfr/cisd0602.pdf. Information in today’s document 

supersedes the earlier guidance, but CISD-06-02 remains relevant on topics not addressed here. 

The content of this guidance responds to inquiries that EPA received since publication of 

CISD-06-02. In particular, there have been many questions about how to use Verify, EPA’s new 

certification data system; how to find documents on the EPA web site; how to certify 

conversions for gasoline vehicles to operate on vegetable oil and hydrogen; how to convert 

vehicles originally certified for gasoline to now operate on ethanol, E85 or intermediate E85-

gasoline blends as flexible fuel vehicles (FFVs); and how to convert heavy-duty engines. The 

guidance also presents new information about establishing test groups for the purpose of 

certifying alternative fuel conversion technologies and about converting vehicles that have 

exceeded their regulatory useful life. 

In keeping with the format of earlier letters on this topic, EPA presents this new 

information in a series of questions and answers. 

EPA has initiated a rulemaking process to update the current alternative fuels conversion 

policy. Under current policy converters must obtain a certificate of conformity to avoid violating 

the anti-tampering provisions of the Clean Air Act. Should EPA change this policy through 

rulemaking, the policies described in this guidance letter and/or in CISD-06-02 could potentially 

change. If you would like to receive information about EPA's rulemaking activity or other 

changes related to our alternative fuels conversions policy, please visit: 

http://epa.gov/otaq/consumer/fuels/altfuels/altfuels.htm and sign-up for e-mail updates using the 

link to “Enviroflash” and selecting “Alternative Fuel Vehicle Conversions.” 
Questions regarding this letter and its Attachment pertaining to light-duty vehicle 

conversions should be directed to Martin Reineman at reineman.martin@epa.gov. Questions 

regarding heavy-duty vehicle and nonroad engine conversions should be directed to Greg 

Orehowsky at: orehowsky.gregory@epa.gov. 

Sincerely, 

Karl J. Simon, Director 

Compliance and Innovative Strategies Division 

Office of Transportation and Air Quality 

Enclosure 
Enclosure to CISD-09-14 

Questions and Answers 

The answers to the questions presented here are based on 40 CFR Parts 80, 85, 86, 88, 600 and 

the Clean Air Act as Amended. 

Questions applicable to all types of fuel conversions 

1. What is the distinction between vehicle certification and engine certification for 

aftermarket fuel conversions? Are the EPA contacts different? 

Ans. Vehicle certification is required for new vehicles up to 14,000 pounds gross vehicle 

weight (GVW) using Otto cycle engines. Vehicle certification is also required for new 

diesel cycle vehicles with GVW up to 8,500 pounds. New diesel vehicles between 8,500 

and 14,000 pounds may be optionally certified using either chassis test standards and test 

procedures, or engine test standards and test procedures. Engines in vehicles of any fuel 

type with a GVW over 14,000 pounds GVW must be engine dynamometer certified. 

Since the certification weight class requirements have changed over time, fuel converters 

should examine the Original Equipment Manufacturer’s (OEM) application for 

certification to determine if a given vehicle or engine was originally vehicle or engine 

certified. Fuel conversions must be certified in a manner consistent with how the OEM 

certified the vehicle or engine. If the vehicle was chassis certified the fuel conversion 

must also be chassis certified. If the vehicle has an engine certification, the fuel 

conversion must be engine certified. 

Vehicle certification of fuel conversions is administered by EPA’s National Vehicle and 

Fuel Emissions Laboratory in Ann Arbor, MI. The EPA vehicle certification contact is 

Martin Reineman. His e-mail address is: reineman.martin@epa.gov. Engine certification 

of fuel conversion is administered in EPA’s Washington, DC office. The EPA engine 

certification contact is Greg Orehowsky. His e-mail address is: 

orehowsky.gregory@epa.gov. 

2. When must vehicle fuel converters begin certifying through EPA’s Verify data system? 

Ans. Vehicle converters are required to submit applications for certification through the Verify 

data system beginning with the 2010 model year. For most converters, applications for 

2009 model year certificates of conformity will continue to be processed outside of 

Verify. Information on the Verify data entry process may be found at: 

www.epa.gov/otaq/verify/publications.htm. To receive information and updates about 

the Verify data system sign up for the Verify Listserver at: 

http://www.epa.gov/otaq/verify/documents/420b07002.pdf. 
3. Is the EPA certification and data entry process for converting engines to alternative fuels 

the same for converting vehicles to alternative fuels? 

Ans. No. Heavy-duty highway engines are currently certified though the FileMaker based 

Information Management System (IMS). Information on the engine certification and 

data entry process can be found at: http://www.epa.gov/otaq/hd-hwy.htm. 

4. The Verify data entry process is complex as are the EPA vehicle and engine certification 

processes. Does EPA provide assistance to fuel converters who are new to both 

processes? 

Ans. Yes. The Verify helpline is available to assist with Verify data entry issues and may be 

contacted by e-mail at: verifyhelp@csc.com or by phone at: 888-890-1995. The EPA 

certification staff can address many questions about the certification process, but fuel 

converters new to the process may well benefit from the assistance of technical 

consultants who are familiar with certification testing requirements and with preparation 

of the documentation required for EPA applications for certification. 

5. Where does one find information on federal or state tax credit or rebate policies for 

aftermarket fuel conversions? 

Ans. Information on federal tax credit policies may be found at the Internal Revenue Service 

web site: http://www.irs.gov. When at that website, search for “alternative fueled 

vehicles.” Information on individual states’ policies with respect to credits and rebates 

must be addressed to the state in question, likely through that state’s tax or revenue 

agency. 

6. What are the OEM's positions on warranty coverage for vehicles converted to operate on 

alternative fuels? 

Ans. The OEMs differ on this issue, and warranty coverage may change over time. Therefore, 

vehicle owners should examine the language in their OEM warranty to understand the 

specific warranty coverage and responsibilities applicable to their vehicle. 

7. Is the certification process the same for any aftermarket conversion, regardless of 

alternative fuel type? 

Ans. Yes. Fuel conversions of OEM vehicles to any alternative fuel must follow the 

requirements in Part 86 of the Code of Federal Regulations (CFR). However, there are 

inherent differences among fuels that can affect test procedures and other detailed fuelspecific requirements that are not explicit in the regulations. For example, test fuel 

specifications for E10 and E85 are not defined in Part 86, Subpart B. Therefore, it is 

important to discuss specific testing issues that are not explicitly described in the CFR in 

advance with an EPA certification representative. 
8. Have there been any changes to the EPA onboard diagnostics (OBD) approval process 

for aftermarket fuels converters? Why is OBD compliance for fuel converted vehicles so 

important? 

Ans. No. Fuel converters are responsible for meeting the EPA OBD regulations in 40 CFR § 

86.1806-05 and 86.007-17. Converters must demonstrate that aftermarket changes to the 

OEM fuel control system have not affected MIL (malfunction indicator light) 

illumination thresholds and that the OBD system will continue to function properly while 

operating on the new fuel. Converters may contact EPA with specific OBD questions. 

A functional OBD system is important in any vehicle, including a converted vehicle, to 

alert the vehicle owner to malfunctions that could cause excessive emissions. States with 

vehicle inspection programs rely almost completely on interrogating the OBD system to 

ensure that there are no emissions problems. 

9. Is the EPA certification process for aftermarket fuel converters the same in California or 

states that have adopted California vehicle emission standards? 

Ans. No. California has it's own requirements for aftermarket fuel conversions. Conversions 

of new vehicles in California are administered through California’s light-duty vehicle and 

truck certification staff. The contact for new vehicle certification in California is Duc 

Nguyen, who may be contacted at: dnguyen@arb.ca.gov. Conversions of in-use vehicles 

are administered through a different department. The contact for these vehicle 

conversions is Rose Castro, who may be contacted at: rcastro@arb.ca.gov. For states 

other than California that have adopted provisions or standards from the California 

vehicle emissions program, contact the individual state in question to learn the specifics 

regarding their policies on fuel conversions. 

10. How does the EPA “test group” concept relate to the real world vehicles? 

Ans. The concept of “test group” was created for vehicle certification purposes and is not 

necessarily easy to associate with “real-world” groupings of vehicles. Test groups 

typically include vehicles with nearly identical engine, emission control, and fuel system 

design characteristics. OEMs designate test groups at the time of certification. The 

characteristics OEMs must evaluate when placing vehicles in test groups can be found in 

40 CFR § 86.1827. Examples of OEM test groups are listed in the Green Vehicle Guide 

under the column heading “Underhood ID.” You can download the guide at: 

http://www.epa.gov/greenvehicles/Download.do 

11. Given that converters may use the same basic fuel system design across multiple model 

years, various manufacturers, and various model types, is it possible to certify a product 

for several OEM test groups or engine families? 
Ans. Yes. Under certain circumstances EPA will now allow fuel converters to combine 

certain OEM test groups into a single fuel converter test group on a case-by-case basis. 

EPA will allow converters to combine OEM test groups if criteria in 40 CFR §§ 86.1820-

01 and 86.1827-01 are followed. EPA will consider allowing OEM test groups to be 

combined if the following criteria are met for each fuel converted test group: 

1) Same original manufacturer and model year 

2) Same OBD group 

3) Same vehicle classification (e.g. LDV, LDT, HDV) 

4) Same combustion cycle 

5) Same engine type (e.g. piston, rotary) 

6) Engine displacements within 15% of largest displacement or 50 CID, whichever is 

largest 

7) Same number of cylinders 

8) Same arrangement of cylinders 

9) Same fuel type (e.g. diesel/gasoline) 

10) Same fuel metering system (e.g. throttle body injection vs. port injection) 

11) Same basic catalyst construction (e.g. metal vs. ceramic substrate) 

12) All converted vehicles are subject to the most stringent emission standards used in 

certifying the OEM test groups. 

13) The fuel converter exercised good engineering judgment when combining OEM test 

groups. 

Advance EPA approval is required for fuel converters to combine OEM vehicle test 

groups. EPA must also approve the selection of a worst case test vehicle among the 

combined OEM test groups. Fuel converters may need to contact EPA to determine if 

the OEM test groups are in the same OBD test group because this information is not 

typically publically available. 

EPA will also allow fuel converters to combine certain OEM heavy-duty engine families 

into a single fuel conversion test group. EPA will allow converters to combine OEM 

engine families if the following criteria are met for each fuel converted test group: 

1) Same original manufacturer 

2) All converted vehicles are subject to the most stringent emission standards. For 

example, 2005 and 2007 heavy-duty diesel engines may be in the same family if they 

meet the most stringent (2007) standards. 

3) Same service class (e.g. LHDDE, MHDDE, HHDE) 

4) Same combustion cycle 

5) Method of air aspiration 

6) Engine displacements within 15% of largest displacement or 50 CID, whichever is 

largest 

7) Same number of cylinders 

8) Same arrangement of cylinders 

9) Same fuel type (e.g. diesel/gasoline) 
10) Same fuel metering system (e.g. mechanical direct or electronic direct injection) 

11) Same basic catalyst/filter construction (e.g. metal vs. ceramic substrate) 

12) The fuel converter must use good engineering judgment when combining OEM 

engine families 

13) Same OBD group after 2013. 

14) Same emission control technology (e.g., internal or external EGR) 

Once you have identified the engines to be included in the conversion test group, select 

the highest emitting engine, pre-conversion, to be the test engine for the group. 

12. Where can one find which manufacturers have been issued EPA certificates for 

aftermarket vehicle and engine fuel conversions? 

Ans. Certificates for aftermarket vehicle conversions may be viewed on the EPA Document 

Index System (DIS). The DIS search field called “model year” refers to the year in 

which the certificate is valid. Therefore, multiple EPA model year searches may be 

necessary to find conversion certificates for a particular OEM model year vehicle. 

Information on the DIS is updated periodically but you may need to contact EPA or the 

fuel converter directly for more recent certification information. Aftermarket alternative 

fuel certificate holders for a particular EPA model year may be viewed by going to: 

www.epa.gov/dis. When at the DIS: 

Select “Certificates of Conformity” in the list of Document types 

Select “Alternative Fuel Conversions” in the list of Industry types 

Select the desired EPA certificate (not vehicle) model year from the Model Year list 

Select “All” in the Manufacturers list 

 Select “Search” 

OEM certificates may be accessed in a similar manner by selecting “Light-Duty Vehicles 

and Trucks” in the list of industry types instead of “Alternative Fuel Conversions,” and 

by selecting the desired vehicle manufacturer instead of “All” in the Manufacturer list. 

Certificates for aftermarket engine conversions may be found at: 

www.epa.gov/otaq/certdata.htm. 

13. Where can one find the OEM or fuel converters’ applications for certification? 

At present, applications for aftermarket conversion certificates are not on the DIS, but 

will be in the near future. OEM applications are posted on the DIS and may be accessed 

as follows: 
Select “Applications” in the list of Document types 

Select “Light-Duty Vehicles and Trucks” in the list of Industry types 

Select the desired EPA model year from the Model Year list 

Select the desired OEM manufacturer from the Manufacturers list 

Select “Search” 

Vehicle certificates and applications not found on the DIS may be obtained by contacting 

EPA’s Freedom of Information officer Fred Hart at hart.frederick@epa.gov. Information 

on heavy-duty engines not published on an EPA website may be obtained through the 

Freedom of Information Act by contacting Robert Doyle at doyle.robert@epa.gov. 

14. Does EPA have authority to conduct in-use testing on fuel converted vehicles and 

engines? 

Ans. Yes. 

15. Is a Vehicle Emission Control Information (VECI) label required to be displayed under 

hood for an EPA certified fuel converted vehicle? Is there a similar requirement for 

Engine Family labeling of fuel converted engines? 

Ans. Yes. The conversion kit installer must apply a second VECI label next to or near the 

original OEM underhood VECI label, which should remain in place. The secondary 

VECI label is a requirement for all EPA-certified fuel converted vehicles. States that 

have vehicle inspection programs may deny registration if there is not a valid VECI label 

which links the fuel converted vehicle to an EPA certificate. The label should clearly 

indicate which fuel the converted vehicle operates on, the name of the manufacturer of 

the fuel conversion system, the installer of the aftermarket fuel system if different from 

the fuel system manufacturer, the converter’s test group name for the specific vehicle, 

and the date the conversion system was installed. There are analogous labeling 

requirements for converted engines. 

16. Do you need to obtain a certificate of conformity to convert nonroad equipment and 

stationary engines to alternative fuels? 

Ans. Yes. Since EPA’s certification policies for non-road sources and stationary sources 

ensure compliance with emission standards for the full useful life of the regulated 

emission source, certification is required to demonstrate compliance with emission 

standards when converting a vehicle to operate on an alternative fuel. 

17. What are EPA’s fuel conversion policies with respect to vehicles outside of EPA’s 

defined full useful life? 
Ans. EPA policy exempts alternative fuel converters from the Clean Air Act prohibition 

against tampering if they obtain a certificate of conformity for the conversion. However, 

the certification process may not be appropriate for vehicles outside their regulatory full 

useful life. EPA recognizes this inconsistency and has initiated a rulemaking process to 

update the policy. The rulemaking will identify alternate regulatory pathways for 

exemption of legitimate alternative fuel conversions from the prohibition on tampering. 

During this interim period while we reconsider our existing regulations, current policy 

remains in place. This means that until a new policy is finalized, no certain protection 

against a tampering charge exists for converters of outside useful life vehicles. A prudent 

course of action for such converters may be to demonstrate through reliable testing that 

the conversion does not increase emissions, and to maintain records documenting test 

results. We recommend that converters with further questions about the Clean Air Act 

tampering prohibition contact EPA’s Office of Compliance and Enforcement Assistance 

at: http://www.epa.gov/compliance/basics/index.html. 

Questions about conversion to specific fuel types and about fuel additives 

Fuel Additives 

18.1 What is a fuel additive? 

Ans. 40 CFR Part 79.2 defines a fuel additive as “... any substance, other than one composed 

solely of carbon and/or hydrogen that is intentionally added to a fuel...” Fuel additives 

to on-road gasoline and diesel fuels must be registered with the EPA. 

18.2 Does adding a registered fuel additive to gasoline or diesel fuel require vehicle fuel 

conversion certification? 

Ans. No, as long as 1) there are no changes to the vehicle's engine or emission system, 2) the 

additive is registered by EPA, and 3) you only add the quantity allowed under additive 

registration. 

18.3 How do I register a fuel additive? 

Ans. The registration requirements depend on the specifics of the additive. Please see EPA 

Form 3520-13 for further information. The form and additional information are available 

at: http://www.epa.gov/otaq/regs/fuels/ffarsfrms.htm. 

Ethanol 

19.1 What concerns does EPA have about aftermarket fuel conversions to E85? 

Ans. OEM E85 flexible fuel vehicles (FFVs) frequently use E85 fuel system components that 

differ in fuel delivery capacity, calibration, and material composition from the fuel 

system components used in gasoline-only vehicles. In some cases OEMs will use E85-

compatible materials and design specifications in gasoline-only vehicles to avoid the 
extra costs associated with maintaining two types of part inventories. If these OEM 

vehicle-specific design differences are not understood and taken into consideration when 

converting a gasoline vehicle to E85, emission and vehicle performance problems may 

result. 

19.2 What components differ between OEM gasoline and E85 fueled vehicles? 

Ans. The component differences between OEM gasoline and E85 FFVs vary as a function of 

manufacturer, model year, and test group. Since the 1996 model year, all light-duty 

vehicles have been designed to accommodate E10 – a mixture of 10% denatured ethanol 

and 90% gasoline. However, unlike a vehicle designed to accommodate E10 fuels, a 

vehicle designed to use E85 and intermediate blends may require design changes in any 

or all of the metals, elastomers, and polymers used in the fuel supply system from the 

fuel pipe inlet to the fuel injectors and intake manifold. Software calibration changes to 

the computer controlled fuel supply are also necessary to account for ethanol’s reduced 

volumetric energy content and unique stoichiometry. Depending on the test group, fuel 

pumps, fuel injectors, and other key components in the fuel supply system may need to 

be changed to accommodate the need for greater fuel delivery when using E85. 

19.3 What are the considerations that go into designing E85 vehicles? 

Ans. The challenge of properly designing E85 vehicles or converting gasoline-fueled vehicles 

to E85 begins with understanding ethanol’s unique chemical and physical properties 

relative to gasoline. The principal design considerations which must be properly 

managed include ethanol’s solvency of organic materials, the potential for galvanic 

corrosion of dissimilar metals due to ethanol’s high electrical conductivity relative to 

gasoline, hydrocarbon permeation, and seal failure if swelling of gaskets and O-rings 

occurs. 

19.4 How do aftermarket fuel converters assure EPA that proper components are being used 

when converting a gasoline-fueled vehicle to E85? 

Ans. On a test group specific basis there are four ways: 

1) A converter could use the same OEM parts that the OEM used in the E85 FFV. 

2) A converter could provide information to demonstrate that the fuel system part 

numbers for the OEM gasoline vehicle and a similar vehicle which the OEM sells as an 

E85 FFV are identical. Identical part numbers demonstrates that the gasoline-fueled 

vehicle was also designed with E85 compatible parts. The comparison between part 

numbers is best performed by comparing dealer or OEM part numbers. 

3) The fuel converter could provide whole vehicle durability data using EPA standard 

durability testing protocols published in 40 CFR Part 86, Subpart S. For example, having 

passing emission data and knowing that the emission control system, fuel system, and 

other powertrain components did not experience failure of components during the 

durability aging would be adequate. 
4) Proof of component durability may be accepted by EPA in the form of an analysis 

demonstrating that the components in the gasoline-fuel system are E85 compatible. Such 

a document would need to come from an OEM or a Tier 1 parts supplier, or the 

equivalent. Documentation or analyses should include references to recognized standard 

industry practices, for example, reference to testing methods for metallic materials or 

polymers described by the Society of Automotive Engineers. 

19.5 Would EPA be satisfied if the converter extends the OEM’s base vehicle warranty to 

cover any concerns due to the installation of the conversion kit or the use of ethanol in 

the OEM gasoline-fueled vehicle? 

Ans. No. Simply extending the base-vehicle warranty does not completely address concerns 

about component compatibility. The concern with offering a limited warranty extension 

of time or mileage to the OEM base vehicle warranty is that a component problem may 

occur outside of the extended warranty limits. 

19.6 Does EPA share the same concerns it has regarding component compatibility in E85 

conversions with other types of fuel conversions, such as gasoline-to-CNG or gasolineto-LPG conversions? 

Ans. Yes. Ensuring that fuel conversions use components that are durable for the full useful 

life of the vehicle is important for any alternative fuel because, unlike conventional large 

volume OEMs, fuel converters are a type of small volume manufacturer. As such, they 

have neither upfront durability demonstration requirements nor in-use testing 

requirements. EPA recommends that converters resolve component compatibility issues 

before conducting emission or OBD testing. For example, if a conversion to CNG 

requires changes to the powertrain, such as installing a different type of intake or exhaust 

valve or valve seat, EPA would expect such modifications to be part of the fuel 

conversion requirements. 

19.7 What emission tests does EPA recommend for certification of an E85 conversion? 

Ans. The types of emission tests EPA recommends will depend on the configuration of the 

OEM vehicle and on the nature of modifications involved in its conversion. If the 

converted vehicle operates as a flexible fuel vehicle (e.g. capable of operating on 

gasoline, E85, or any blend of the two), exhaust testing will be required on both E85 and 

on the original fuel. Testing for evaporative emissions could be required on E10, which 

is the worst-case fuel for evaporative emissions. If the converted vehicle operates only as 

a dedicated E85 vehicle testing would only be required on E85. 

At minimum, recommended testing would include running FTP and Highway test cycles. 

However, as indicated above, the appropriate testing protocol will be technology specific 

and other exhaust as well as evaporative emissions cycles might be recommended. E85 

converters should examine the OEM application and discuss with EPA any planned 

modifications to the OEM configuration before establishing testing plans. Decisions 
regarding what tests are required must be approved by EPA in advance. 

19.8 Have there been any test procedure changes with respect to measuring NMOG (nonmethane organic gas) exhaust or OMHCE (organic material hydrocarbon equivalent) for 

the evaporative emission, running loss, or ORVR tests? 

Ans. EPA regulations still reference California Air Resources Board test procedures for 

determining NMOG. EPA regulations allow the use of equivalent or better practices 

when supported by data and approved in advance by the EPA Administrator. Since the 

California NMOG procedures were proposed, OEMs have been granted approval to use a 

photo acoustic multi-gas analyzer called an Innova to measure alcohols from an E85 

vehicle. EPA uses the Innova methodology for measuring alcohols at its Ann Arbor 

laboratory. 

Vegetable Oil 

20.1 What are EPA’s policies with respect to diesel-to-vegetable oil conversions? Are they the 

same for virgin and waste vegetable oil? 

Ans. EPA’s policy is the same for both virgin and waste vegetable oil. Like other fuel 

conversions, aftermarket systems that allow diesel vehicles to run on either virgin or 

waste vegetable oil fuel must be certified. This is necessary because diesel engines 

cannot operate on vegetable oil without significant modification to the fueling system. 

As part of the certification application, EPA would expect the fuel converter to 

demonstrate that the converted vehicle will meet standards despite potential variation in 

vegetable oil fuel properties. 

20.2 Can pure vegetable oil be “registered” as a diesel fuel with EPA? 

Ans. No. Vegetable oil is not classified as a type of diesel fuel. Vegetable oil and diesel fuel 

differ substantially in their chemical and physical properties. It may be possible to 

register vegetable oil as a diesel fuel additive if the additive volume is less than 5%. 

20.3 Can I add a small amount of vegetable oil to my diesel fuel as a diesel fuel additive? 

Ans. Yes, assuming that you meet the following two criteria: 

1) There are no engine or emission control system modifications to your vehicle. 

2) The vegetable oil is registered with EPA as a diesel fuel additive. EPA may register 

vegetable oil as a diesel fuel additive at a volume of 5% or less. For information about 

registering vegetable oil as a diesel fuel additive, please visit EPA’s fuel registration web 

site at http://epa.gov/otaq/regs/fuels/ffarsfrms.htm. 
Hydrogen 

21.1 What are EPA’s policies with respect to converting OEM vehicles to 100% hydrogen? 

Ans. Aftermarket conversions to hydrogen must certify under the appropriate standards and 

testing requirements in 40 CFR Part 86. However, a few test procedures are not required 

since hydrogen-powered vehicles use a closed fueling system no evaporative emission 

data submissions are necessary. Additionally, because a pure hydrogen-powered vehicle 

has no compounds in the fuel that contain carbon, there are no reporting requirements for 

CO or NMOG. 

21.2 What are EPA’s policies on adding hydrogen generator systems, such as hydrolysis 

systems (often referred to as HHO systems) to an OEM certified vehicle or engine? 

Ans. EPA’s policy depends on the design of the HHO system and whether modification to the 

OEM configuration is involved. Any HHO kit that requires engine or fueling system 

modifications, or that includes components that alter the emission control system, would 

require EPA certification to avoid a potential violation of anti-tampering provisions of 

the Clean Air Act. In addition, if the system introduces into the engine any elements 

other than carbon and/or hydrogen, fuel additive registration would be required. See 

questions 18.1-18.3 for more information. 

Most hydrogen generator systems produce less than 1% of total engine fueling 

requirements and many less than 0.1%. EPA does not view these systems as a type of 

fuel switching, but rather considers them a type of aftermarket device. EPA does not 

certify aftermarket devices. Manufacturers may voluntarily choose to have their 

aftermarket system evaluated under EPA’s “511 Program,” which refers to EPA’s testing 

program of aftermarket devices, formerly conducted under authority of Section 511 of the 

Motor Vehicle Information and Cost Savings Act. More information on the 511 Program 

may be found at: http://www.epa.gov/otaq/consumer/reports.htm. 

Electricity 

22.1 What are EPA’s policies with respect to converting hybrid electric vehicles to plug-in 

hybrid electric vehicles? 

Ans. EPA’s conversion policy applies to hybrid electric-to-plug-in conversions. Certification is 

required to ensure that the converted plug-in hybrid will meet applicable emission standards 

and will remain clean and durable for its full useful life. This is necessary because any 

change to an OEM-certified configuration could affect the emission control system and 

could be considered a tampering violation. In the case of an aftermarket plug-in hybrid 

conversion, for example, it is possible that the altered interaction between the internal 

combustion engine and the battery electric system could cause more “cold starts” of the 

internal combustion engine, thereby increasing emissions relative to the OEM vehicle.