In late January 2026, the Trump administration announced that it will no longer criminally prosecute manufacturers, distributors and users of so-called “defeat devices” which are used to disable air emissions control systems in diesel-powered vehicles. An example would be removing or disabling diesel exhaust fluid (“DEF”) system. Shortly after that announcement, the Environmental Protection Agency (“EPA”) issued new guidance clarifying that farmers and repair shops may temporarily override emission control systems for the purpose of repairing agricultural vehicles. Although the federal government will no longer pursue criminal violations for the use of defeat devices, civil penalties for the use of such devices remain on the table. Those who own and operate diesel vehicles, particularly in an agricultural setting, should be aware of these developments and their implications.
Background
The Clean Air Act (“CAA”) is the primary federal air quality law in the United States. It was initially enacted in 1963 for the purpose of protecting and enhancing the nation’s air quality and preventing air pollution. 42 U.S.C. § 7401. To accomplish that purpose, the CAA has developed a variety of statutory programs aimed at addressing both specific air pollutants and the various sources of those pollutants. Many of those programs are targeted at reducing mobile source pollutants which are the emissions produced by internal combustion engines in motor vehicles such as cars and trucks.
Under one of the CAA’s provisions regarding mobile source pollutants, EPA is authorized to set limits on the amount of pollutants that motor vehicles, including diesel vehicles, can emit. 42 U.S.C. § 7521(a)(1). Diesel engines are known to emit nitrogen oxides and particulate matter both of which are pollutants that EPA regulates under the CAA. EPA has adopted a variety of regulatory requirements setting limits on how much of each pollutant a diesel engine may emit. To meet these standards, diesel engine manufacturers have developed various emissions control devices to ensure that newly manufactured diesel vehicles comply with the CAA. Additionally, the CAA requires vehicle manufacturers to install on-board diagnostic systems which can help monitor a vehicle’s emissions levels. 42 U.S.C. § 7521(m)(1). These diagnostic systems will alert the driver if a truck’s emissions exceed legal limits and, if the alert is not addressed, the system may either shut the vehicle down or reduce its maximum speed to as low as five miles an hour.
Importantly, it is a violation of the CAA for any person to “remove or render inoperative” any vehicle device or design element that was installed to fulfill CAA requirements. 42 U.S.C. § 7522(a)(3)(A). The CAA also prohibits anyone from manufacturing, selling, or installing any device intended to “bypass, defeat or render inoperative” any component of a vehicle that is designed to facilitate CAA compliance. 42 U.S.C. § 7522(a)(3)(A). This prohibition includes “defeat devices” that can be used to remove or disable on-board diagnostic systems installed in diesel vehicles. The CAA exempts actions to disable or bypass vehicle components necessary to achieve CAA compliance if the action is a “necessary and temporary procedure to repair” any element of the vehicle provided that the action results in proper functioning of any CAA-required vehicle component after the repair is complete. 42 U.S.C. § 7522(a)(5). Such repair actions are not considered violations of the CAA and do not carry any penalties.
Use of a defeat device in a diesel vehicle, such as removing or disabling a DEF system, is subject to both civil and criminal penalties. The CAA assigns civil penalties of up to $25,000 for any vehicle manufacturer or dealer who installs a defeat device, and penalties of up to $2,500 for any other person who installs such a device. 42 U.S.C. § 7524(a). Though not criminal in nature, these civil penalties can be cumbersome. In 2022, EPA reached a settlement agreement with an automotive parts manufacturer and distributor to halt sales of defeat devices and pay civil penalties of $1.6 million.
Use of a defeat device, or any other means of “tamper[ing] with” a vehicle’s emissions monitoring system, is also considered a felony under the CAA and anyone convicted of such a felony may face up to two years in prison. 42 U.S.C. § 7413(c)(2)(C). For example, in 2025, a federal court sentenced a man from Indiana to 4 months in prison and issued him a $25,000 fine for disabling pollution control software on diesel trucks. The sentence was issued after the man pled guilty. Prosecutors had originally sought an 18-month prison sentence and a $100,000 fine.
Recent Developments
Over the past few weeks, the federal government has made important announcements regarding its enforcement of the CAA and its prohibition on disabling or bypassing emission control systems. In late January, the Department of Justice (“DOJ”) announced that it would no longer enforce criminal penalties against those who use defeat devices on diesel vehicles. Then, in early February, EPA released a new guidance document clarifying its position on disabling or bypassing emission control devices for the purpose of making repairs.
On January 21, the DOJ announced on social media that it is exercising its prosecutorial discretion and will no longer bring criminal charges against those who violate the CAA by tampering with or disabling emissions control monitoring systems in motor vehicles. According to reporting on the matter, an internal memorandum was circulated within DOJ announcing the policy change. The document referred to a legal argument raised by a defendant who was indicted by the federal government in 2021 for installing defeat devices on diesel vehicles for clients of the defendant’s autobody shop. The defendant was convicted by a jury in 2024 of eleven felony violations of the CAA and was sentenced to four years of probation and a $10,000 fine. The defendant appealed the conviction to the Ninth Circuit Court of Appeals. On appeal, the defendant argued that the CAA does not require the maintenance of on-board diagnostic systems. The defendant claimed that the government had misinterpreted the provision of the CAA which criminalizes tampering with emissions monitoring devices. The text of the statute assigns criminal penalties to any person who purposefully “falsifies, tampers with, renders in accurate, or fails to install any monitoring device or method required to be maintained or followed under [the CAA].” 42 U.S.C. § 7413(c)(2)(C). The defendant argued that on-board diagnostic systems are not “monitoring devices” under the CAA because the systems do not directly monitor vehicle emissions but instead monitor a vehicle’s emissions control system to detect and report any malfunctions. Because the statutory text of the CAA does not specifically require maintenance of on-board diagnostic systems, the defendant argued that the government could not charge her with a felony for disabling the systems.
According to reporting, DOJ has found this argument persuasive, and it is part of the agency’s reasoning for the policy change. Importantly, the Ninth Circuit has not made a ruling on the defendant’s argument. It is currently not clear whether the Ninth Circuit will hear the argument as the defendant has moved to have the case dismissed following DOJ’s announcement. Although DOJ will no longer seek criminal penalties for the use of defeat devices or other methods to disable on-board diagnostic systems, it did not take civil penalties off the table. EPA may still issue fines for disabling on-board diagnostic systems under its CAA authority. Additionally, it is not clear how long DOJ will hold off on seeking criminal penalties for use of defeat devices. Because DOJ is using its own prosecutorial discretion to cease prosecution, it could reverse its decision in the future. Without a change to the text of the CAA, criminal penalties for the use of defeat devices remain a future possibility.
After DOJ made its announcement, on January 30, EPA released a guidance document clarifying the agency’s policy on temporarily disabling emission control systems to repair or maintain nonroad vehicles such as tractors and other agricultural equipment. The guidance comes in response to a letter that farm equipment manufacturer John Deere sent to EPA in 2025 seeking approval to allow both customers and independent repair technicians to override emission monitoring systems in order to make repairs. In the guidance document, EPA notes that while the CAA prohibits actions to disable or bypass monitoring systems, it also provides an exemption if “the action is for the purpose of repair[.]” Although some manufacturers have interpreted the CAA to prohibit third parties from making vehicle repairs if doing so would require temporary disabling of the emission control system, EPA states that this is a misinterpretation of the statute. According to EPA, the CAA exemption for repairs applies to anyone who is facilitating a repair provided that the monitoring system is restored once the repair is complete.
Going Forward
Both the announcement from DOJ and updated guidance from EPA have created a change in the regulatory landscape for diesel vehicles. While the installation and use of a defeat device in a diesel vehicle is still subject to civil monetary penalties, criminal penalties are off the table at least for now. Those who temporarily disable an emissions monitoring device in a diesel vehicle to make a repair should not face either civil or criminal penalties following EPA’s recent guidance document. The exemption applies not only to vehicle manufacturers, but to anyone who is making the repair. For those who work with diesel vehicles, these announcements provide clarity on what actions are currently considered a violation of the CAA.
To view the text of the CAA, click here.
For more CAA resources from the National Agricultural Law Center, click here.