Questions and Answers

Frequently Asked Questions from 

Owners and Operators of Nonroad 

Engines,Vehicles, and Equipment 

Certified to EPA Standards 

The U.S. Environmental Protection Agency (EPA) has adopted 

emission standards for nearly all types of nonroad engines, vehicles, 

and equipment. This page describes how EPA emission standards affect 

individual owners and operators of these products. 

Why does EPA adopt emission standards for nonroad engines, vehicles, and 

equipment? 

Nonroad engines contribute significantly to air pollution. The emission standards 

address emissions of oxides of nitrogen (NOx), hydrocarbons (HC), particulate 

matter (PM), and carbon monoxide (CO). These emissions help form smog and 

include toxic compounds such as benzene, so reducing them will benefit our health 

and environment. In the Clean Air Act, Congress requires us to set emission standards that address these problems. 

Does my current nonroad engine, vehicle, or equipment need to meet these 

regulations? 

Manufacturers must ensure that each new engine, vehicle, or equipment meets the 

latest emission standards. Once manufacturers sell you a certified product, no further 

effort is required to complete certification. If products were built before EPA emission 

standards started to apply, they are generally not affected by the standards or other 

regulatory requirements. See Table 1 for a listing of when EPA emission standards 

started to apply. We never require owners to retire their old engines, vehicles, or 

equipment. 

Office of Transportation and Air Quality 

EPA-420-F-18-004 

February 2018 
 

Questions and Answers

What requirements apply to owners and operators of certified products? 

A key part of the regulations that applies to you is the tampering prohibition—you may not 

disable any emission controls installed on certified engines, vehicles, or equipment. This would 

apply for removing emission control devices, adding or modifying hardware or software that 

increases emissions (of any pollutant), reprogramming onboard computers, or operating engines 

without any needed supplies such as Diesel Exhaust Fluid. Manufacturers explain in their owner’s manual what type of emission controls exist for each model; they may also specify some 

minor maintenance that must be done to keep emission controls working properly. For restrictions 

and recordkeeping requirements that apply for rebuilding engines and performing maintenance 

on certified products, see “How to Maintain or Rebuild Engines Certified to EPA Standards,” 

(EPA-420-F-18-003, February 2018) which is available at www.epa.gov/regulations-emissionsvehicles-and-engines/regulations-emissions-nonroad-vehicles-and-engines. 

Similarly, EPA regulations prohibit defeat devices—you may not make, sell, or install any part 

that bypasses, impairs, defeats, or disables the control of emissions of any regulated pollutant. 

Since manufacturers have the primary responsibility to meet emission standards for their products, 

you generally have no requirements to achieve a certain level of emission control or to re-certify. 

However, you must meet additional requirements in two special circumstances: 

• You may need to use certified kits or systems when remanufacturing locomotive engines

or marine diesel engines.

• In the case of Marine SI engines (40 CFR part 1045), Recreational vehicles (40 CFR

part 1051), and Small SI engines (40 CFR part 1054), you must re-certify if you upgrade your engine to operate on a different fuel. For fuel conversions with other types of

nonroad engines, vehicles, or equipment, you may need to do testing to show that the

conversion is not considered tampering, but you do not need to re-certify.

What kind of emission controls does EPA require? 

We don’t tell manufacturers what emission controls to use to comply with the regulations, but 

we rely on testing information from engines equipped with specific technologies to establish the 

emission standards. Manufacturers may use these anticipated technologies, or they may find 

better ways to meet emission standards. 

Manufacturers of diesel engines have typically met the standards with more careful control of 

intake air and fuel injection, with some exhaust gas recirculation. Long-term standards for many 

of these engines will generally involve additional use of aftertreatment devices such as diesel 

particulate filters (DPF) and selective catalytic reduction (SCR). 

Most Large SI engines and many Marine SI engines use automotive-type technologies, including 

closed-loop fuel injection and three-way catalytic converters. For other engines, manufacturers 

will optimize air-fuel mixtures and make other internal engine changes. We expect continued 

use of two-stroke engines in the following cases: (1) outboard and personal watercraft marine 

engines may use direct-injection two-stroke engine technology, which avoids the most prob2 
Questions and Answers

lematic aspects of two-stroke combustion; (2) to maintain lightweight performance, Handheld 

Small SI engines will typically continue to use two-stroke engines, though these engines will 

generally have catalysts to reduce the amount of unburned fuel from escaping through the 

exhaust as hydrocarbon emissions; and (3) some two-stroke snowmobile engines will likely continue to be available, depending on ongoing efforts to improve the performance characteristics 

of four-stroke snowmobile engines. 

For gasoline-fueled products, we have also adopted requirements to control permeation emissions from fuel systems. We expect these requirements to lead to the use of improved materials 

to prevent fuel from escaping through fuel tanks and hoses into the atmosphere. This should 

noticeably reduce the smell of gasoline around these vehicles and equipment. 

How will these controls affect performance and safety? 

As part of the rulemaking process, we evaluate potential safety issues related to new standards 

to make sure not to adopt emission standards that would cause manufacturers to use emission 

controls that add new risks to operating vehicles or equipment. As always, it is important to 

take proper precautions when using engine-powered vehicles or equipment. 

Meeting emission standards adds to the engine designer’s challenge. This might lead to some 

trade-offs with respect to power or efficiency; however, there are many examples of design 

engineers coming up with ways to add emission controls in a way that significantly improves 

engine power and efficiency while reducing emissions. Over time, engineers will work to 

improve designs to reduce or eliminate any remaining trade-offs. 

Do EPA regulations affect where I can use my nonroad vehicle or equipment? 

No. These regulations do not include any specific restrictions about where you can use your 

nonroad vehicle or equipment. They address only the permissible emission rates from new, 

certified products. 

State and local governments have limited authority to set emission standards for new products; 

however, they may adopt regulations that restrict the use and operation of most products that 

are no longer new. EPA generally has no involvement with such restrictions. 

Do EPA regulations apply in California? 

California has adopted its own emission standards for certain types of new nonroad engines, 

vehicles, or equipment. In those cases, manufacturers must certify their products with the 

California Air Resources Board; these products are also certified with EPA even if no additional 

requirements apply. 

EPA’s prohibitions against tampering and defeat devices apply to certified products throughout 

the United States, including products that are certified to meet emission standards that apply 

uniquely in California. 

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Questions and Answers

For More Information 

You can access documents related to emission standards for nonroad engines, vehicles, and 

equipment on EPA’s Office of Transportation and Air Quality (OTAQ) website at: 

www.epa.gov/regulations-emissions-vehicles-and-engines/regulations-emissionsnonroad-vehicles-and-engines 

You can also contact the OTAQ library for document information at: 

(734) 214-4311
 

Email: Group_AALibrary@epa.gov
 

Table 1 

Schedule for Application of New Emission Standards for Certifying Engines and Vehicles 

Engine category Engine subcategory Manufacturing date 

after which emission 

standards start to apply 

A. Heavy-duty highway engines — Model year 1970 

B. Locomotives or locomotive 

engines 

— January 1, 1973 

C. Marine compression-ignition 

engines at or above 37 kW 

Commercial: displacement < 0.9 L/cyl Model year 2005 

Commercial: 0.9 < displacement < 2.5 L/cyl Model year 2004 

Commercial: displacement > 2.5 L/cyl Model year 2007 

Recreational: displacement < 0.9 L/cyl Model year 2007 

Recreational: 0.9 < displacement < 2.5 L/cyl Model year 2006 

Recreational: 2.5 < displacement < 5.0 L/cyl Model year 2009 

D. Other nonroad compressionignition engines. Marine compression-ignition engines: Power < 19 kW January 1, 2000 

Marine compression-ignition engines: 19 kW < Power < 37 January 1, 1999 

Nonroad engines: Power < 19 kW January 1, 2000 

Nonroad engines: 19 kW < Power < 37 January 1, 1999 

Nonroad engines: 37 kW < Power < 75 January 1, 1998 

Nonroad engines: 75 kW < Power < 130 January 1, 1997 

Nonroad engines: 130 kW < Power < 560 January 1, 1996 

Nonroad engines: Power > 560 kW January 1, 2000 

E. Marine spark-ignition engines. Outboard Model year 1998 

Personal watercraft Model year 1999 

Sterndrive/inboard Model Year 2010 

F. Recreational spark-ignition 

engines and vehicles 

— Model year 2006 

G. Other nonroad spark-ignition 

engines at or below 19 kW 

— Model year 1997 

H. Other nonroad spark-ignition 

engines above 19 kW 

— Model year 2004 

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