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Tampering and Aftermarket Defeat Devices

Get more information and resources on tampering & aftermarket defeat devices.

On this page:

What is tampering and why does it matter?

Poster: Emissions Tampering is llegal and pollutes our air
Tampering with a vehicle's emissions control system is illegal under the Clean Air Act (CAA) and causes excess emissions of nitrogen oxides (NOx), particulate matter (PM), and other pollutants to the air we breathe. The CAA also prohibits manufacturing, selling, offering for sale and installing aftermarket devices which effectively defeat those controls.

EPA's current National Compliance Initiative (NCI) for 2020-2023, "Stopping Aftermarket Defeat Devices for Vehicles and Engines," focuses on stopping the manufacture, sale, and installation of defeat devices on vehicles and engines used on public roads as well as on nonroad vehicles and engines. EPA has found that tampering is widespread (pdf) (2.6 MB). Both EPA and states are concerned that engines whose emissions control devices are missing or not working are harming public health and the environment, and that they may contribute to states failing to achieve air quality standards.

Tampering can cause a vehicle to emit hundreds to thousands of times more pollution than it otherwise would. Recent EPA investigations indicate that controls on over 500,000 diesel pickup trucks, or about 13% of those registered that were originally certified with emissions controls, have been fully removed or deleted through tampering. The excess NOx emissions from these vehicles is the equivalent of adding 9 million trucks to our roads. Even more pickups could be tampered with, as well as heavy duty trucks and offroad equipment used in agriculture and construction.

Tampering can take two basic forms:

  • Removing hardware, filters and catalysts in the stock emission control system. This hardware can be located in the engine (e.g. Exhaust Gas Recirculation (EGR)) or in the exhaust system (e.g. Diesel Particulate Filter (DPF) or Selective Catalytic Reduction (SCR)).
  • Replacing or altering the software or calibrations that control engine operation, sometimes referred to as "tuning." Tuning may increase engine emissions, allow a vehicle or engine to operate without emissions controls, or prevent the onboard diagnostic system from recognizing that the vehicle or engine is functioning differently than originally designed and certified.

Demand for aftermarket defeat devices is sometimes said to be driven by a desire for:

  • More power & torque
  • Better fuel economy
  • Customization, including the ability to "roll coal"
  • Reduced maintenance cost
  • Avoiding potential downtime for control device regeneration or failure

Vehicle owners may not realize that tampering can void the vehicle warranty.

How does tampering affect air quality and public health?

A "full delete" of the emission controls on a modern heavy-duty diesel pickup truck can cause it to emit as much harmful pollution as 300 trucks with fully functioning emissions controls! Tampering with only some components also leads to significantly elevated emissions of NOx, PM, carbon monoxide, and hydrocarbons. These pollutants contribute to a variety of public health problems, such as premature death in people with heart or lung disease, heart attacks, irregular heartbeat, aggravated asthma, decreased lung function, and respiratory symptoms such as irritation of the airways, coughing, or difficulty breathing.  NOx reacts with sunlight to cause ground-level ozone pollution (smog), so visibility, discomfort and illness may increase in the summer, when people enjoy being outside and traffic increases with travel to vacation and recreation areas.

What does Federal law prohibit?

The CAA contains two relevant requirements – one related to tampering and the other to defeat devices. The following acts (and causing them to occur) are prohibited:

  • For anyone to knowingly remove or render inoperative any device or element of design that had previously been installed on a motor vehicle or engine in order to comply with CAA regulations.

See CAA § 203(a)(3)(A), 42 U.S.C. § 7522(a)(3)(A)

  • For any person to manufacture or sell, or offer to sell, or install, a part or component for a motor vehicle, where
    • A principle effect of the part or component is to bypass, defeat, or render inoperative any device or element of design that had previously been installed on a motor vehicle or engine in order to comply with CAA regulations, and
    • The person knows or should know that such part or component is being offered for sale or installed for such use or put to such use.

See CAA § 203(a)(3)(B), 42 U.S.C. § 7522(a)(3)(B)

The CAA states that it is a crime to knowingly falsify, tamper with, render inaccurate, or fail to install any "monitoring device or method" required under the CAA.  Vehicle Onboard Diagnostics (OBD) systems are a "monitoring device or method" required under the CAA.

See CAA § 113(c)(2)(C), 42 U.S.C. § 7413(c)(2)(C)

Violations are widespread and financial penalties are significant. Those who sell or install devices to defeat emission controls can be fined over $5,000 per defeat device, and dealers can be fined over $5,000 per tampered vehicle. Nationally, EPA has settled over 100 civil tampering cases to date, and the Department of Justice has won jail terms and high fines in criminal cases.

Federal Enforcement

On November 23 2020, EPA updated the Enforcement Policy on Vehicle and Engine Tampering and Aftermarket Defeat Devices. Recent EPA enforcement activity is highlighted in the December 2020 EPA Enforcement Alert "Aftermarket Defeat Devices and Tampering are Illegal and Undermine Vehicle Emissions Controls (pdf)" (284 KB) and the April 30, 2020 press release EPA Highlights Enforcement Actions Against Those Who Violate The Defeat Device and Tampering Prohibitions under the Clean Air Act. A few examples of resolved cases are described below. To read about other closed cases, organized by year, please visit Clean Air Act Vehicle and Engine Enforcement Case Resolutions. Also see Tampering In The News below for new as well as older cases in the news.

Punch It Performance (Supplier)
On January 10, 2020, DOJ and EPA announced a settlement with Punch It Performance and Tuning and associates, manufacturers and sellers of aftermarket devices primarily designed for diesel pickup trucks. The defendants surrendered all intellectual property to the EPA, including programming, files, software, source code, design, instructions, or other information that could be used to manufacture tunes, and to refuse to provide technical support or honor warranty claims for any of their aftermarket defeat devices. Defendants paid a civil penalty of $850,000 due to their limited financial resources, and said they would raise the funds by selling residential real estate properties that they purchased with profits made from the manufacture and sale of defeat devices.

EPA: Punch It Performance Clean Air Act Settlement

Jan 11, 2020, Orlando Sentinel, Deltona man pays $850K settlement for helping cars evade EPA regulations

E.L.M. Repair and Refrigeration (Repair Shop)
On September 18, 2019, E.L.M. Repair and Refrigeration agreed to pay a penalty of $47,592 to settle EPA's claim that E.L.M. tampered with at least 47 elements of heavy-duty diesel engines and sold at least 61 defeat devices. E.L.M. was also made to recall and repair all tampered vehicles, and to develop and execute a compliance plan. The company agreed to spend at least $142,776 on a supplemental environmental project to replace or upgrade old, inefficient wood stoves that also contributed to particulate matter pollution in the area.

Consent Agreement and Final Order (pdf) (833 KB)

Sparhawk (Heavy Duty Fleet and Repair Service)
On April 29, 2019, Sparhawk Truck and Trailer agreed to pay a penalty of $91,000 and developed a compliance plan to settle allegations that they removed or rendered inoperative the engine control modules on 19 trucks with heavy-duty diesel engines (HDDE), some owned by related company Sparhawk Trucking and some by customers. Sparhawk drilled holes into the engine blocks and crankshafts on some trucks. Prior to entering into the settlement, Sparhawk claimed to have spent more than $1 million returning certain trucks to factory settings, and the agreement gives Sparhawk eighty days to either scrap or repair the remaining trucks.

Consent Agreement and Final Order (pdf) (2.3 MB)

Citizen Suits

The CAA contains a provision whereby citizens can bring suit to enforce its terms. A U.S. District Judge ruled in favor of the citizen plaintiffs in a suit brought by Utah Physicians for a Healthy Environment against reality TV stars the Diesel Brothers for removing pollution control equipment from diesel trucks, installing defective emission control equipment, and selling and operating those trucks. Diesel Brothers was ordered to pay $848,000 for 400 violations that contributed to the failure of some counties in northern Utah to achieve attainment with EPA air quality standards. The case was appealed to the U.S. Court of Appeals for the Tenth Circuit, which upheld the lower court ruling.

Ogden, Utah Standard-Examiner: Judge hits Diesel Brothers with $848,000 in penalties for air pollution violations

National Law Review: Tenth Circuit Decision Could Pave the Way for More Frequent Clean Air Act Enforcement

pickup truck spewing smoke
Credit: EPA

What does state and local law prohibit?

Many state and local agencies in the Northeast and beyond also prohibit tampering. States also often have laws prohibiting the sale of new or used vehicles that have been tampered with, and the operation of those vehicles.

Most Northeast states have annual vehicle inspection requirements for passenger vehicles, and the requirement to have vehicles inspected upon change of ownership.  Inspections typically include visual checks to make sure exhaust systems are intact and that OBD systems are working and not showing error codes. Some states also have emissions inspection programs for heavy duty cargo trucks as well. Inspection standards are more stringent in jurisdictions that do not meet federal air quality standards.

EPA and states are also working together to educate those who own, sell, and service vehicles, and those who sell emissions-related products, on how to comply with federal and state laws regarding tampering.

Find more information on Northeast states' requirements and related programs:




New Hampshire

New Jersey

New York

Rhode Island


Frequently Asked Questions (FAQs)

EPA FAQs, including:

  • What is the federally mandated warranty for emission controls on my car?
  • Do those products that claim to improve fuel economy or lower emissions really work? Some say they are EPA-certified.
  • I just bought a used car and discovered the catalytic converter is missing. Is that legal?

Does EPA have any informational materials I can distribute to my students, employees, peers, or the general public?


Does EPA maintain a list that I can check to see if particular hardware or software is EPA compliant?
EPA does not verify or certify any aftermarket devices, so does not list them.

Note: EPA's Mobile Source Enforcement Memorandum No. 1A: Interim Tampering Enforcement Policy (June 25, 1974) (pdf) (583 KB) states that the EPA typically does not take enforcement action for certain conduct that may appear to be a violation of the CAA if the person performing the conduct has a documented "reasonable basis" demonstrating that the conduct does not adversely affect emissions. The EPA has indicated that an Executive Order issued by the California Air Resources Board ("CARB") may be one way to establish a "reasonable basis." CARB is the air agency under California's Environmental Protection Agency that maintains a certification program for aftermarket parts. You can check the CARB list here.

How can I tell if my vehicle has been tampered with? What should I do if I discover that I have purchased a tampered vehicle?
The Minnesota Pollution Control Agency's website has some some generally-applicable advice for consumers on this topic. Also, all states have "lemon laws" intended to help consumers who find they have purchased a defective vehicle.

I didn't tamper with the vehicle, but can I sell it?
Sales and operation of used tampered vehicles are not covered by the CAA. However, the CAA does prohibit the sale of defeat devices and at least one federal court, in a recent citizen suit, interpreted the prohibitions against selling defeat devices to extend to the sale of a vehicle with a defeat device. Further, many states have laws that prohibit dealers from selling (or offering to sell) vehicles/engines that are tampered.  

If I say my truck is only for racing, is that OK?
There is no exemption under the CAA for vehicles used only offroad or only for racing. If the vehicle or engine was originally certified by EPA, the CAA prohibits tampering with it or installing defeat devices. There is no legal pathway to convert a motor vehicle to a competition-use vehicle exempt from the tampering prohibition. However, EPA has indicated that as a matter of enforcement discretion, it is not interested in bringing enforcement actions against vehicle owners for removing or defeating the emission controls of an EPA-certified motor vehicle for the purpose of permanently converting it to a vehicle that is used solely for competition motorsports, and is never driven on public roads.

March 2020 letter from Susan Bodine, Assistant Administrator for Enforcement and Compliance Assurance, to Senator Reed in response to his December 11, 2019 letter concerning the Clean Air Act and converting motor vehicles into vehicles used for competition motorsports (pdf) (3.2 MB)

Additional Resources

EPA presentation "Stopping Aftermarket Defeat Devices (pdf)" (4.6 MB) (recording, starting at 54’49”) at the Northeast Diesel Collaborative Partners Meeting “Federal Tampering Enforcement Updates” (2021)

EPA presentation with the Specialty Equipment Market Association "EPA Tampering Policy - Overview and Discussion (pdf) (2.7 MB)" and video (February, 2021)

EPA presentation "Tampering & Aftermarket Defeat Devices (pdf) (2.4 MB)" to North Central Texas Council of Governments (November 2019)

Specialty Equipment Market Association – Emissions Compliance Resources

Specialty Equipment Market Association (Legislative and Technical Affairs), "Timely Guidance on Government Regulation of Emissions-Related Aftermarket Parts (pdf) (1.1 MB)" (August 2018)

Whitepaper on Tampering and After Market Defeat Devices: An Analysis of Mid-Atlantic State Compliance and Enforcement Options (pdf) (549 KB)

40 CFR Parts 85 and 86: Final Rule for Clean Alternative Fuel Vehicle and Engine Conversions (effective 4/8/2011) Manufacturers of clean alternative fuel conversion systems may demonstrate that they are exempt from the CAA prohibition against tampering for the conversion of some vehicles and engines to operate on a clean alternative fuel.

Tampering in the News

Below please find links to recent news articles.


Who can I contact for more information and assistance?

In the New England states (Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont), you can contact EPA Region 1 staff:
Abby Swaine ( or 617-918-1841)

In the states of New Jersey and New York, as well as Puerto Rico and the U.S. Virgin Islands, you can contact EPA Region 2 staff:
Reema Loutan ( or 212-637-3760)

How can I report suspected tampering to EPA?
Or use the form at