The Nickel Report

The US Department of Justice (DOJ) recently announced it is “exercising its enforcement discretion to no longer pursue criminal charges . . . on allegations of tampering with onboard diagnostic devices in motor vehicles” under the Clean Air Act (CAA or Act). According to DOJ, this exercise of discretion not to criminally prosecute is based on “sound enforcement principles, efficient use of government resources[,] and avoiding overcriminalization of federal environmental law.” DOJ’s announcement is an about-face from years of criminal prosecutions for identical conduct, including an increase of these prosecutions under the first Trump administration. As a result of this new policy, DOJ is now dismissing existing CAA criminal tampering cases—more than a dozen prosecutions thus far—and the decision may impact some 20 or more ongoing investigations. DOJ stated in its announcement that it intends to continue to pursue civil enforcement for tampering cases under the Act in partnership with EPA.

DOJ’s announcement represents the current administration’s latest significant policy shift concerning environmental enforcement. In December 2025, EPA’s Office of Enforcement and Compliance Assurance (OECA) announced the agency’s “Compliance First” approach to environmental enforcement, emphasizing swift, efficient achievement of compliance over punitive or expansive enforcement measures.

The CAA prohibits anyone from manufacturing, offering for sale, selling, or installing any part or component that bypasses or defeats emissions controls. It is also unlawful to knowingly falsify, tamper with, render inaccurate, or fail to install any required “monitoring device or method,” which EPA and DOJ have interpreted in criminal prosecutions to include a vehicle’s on-board diagnostic system. EPA regulations establish the same prohibitions on tampering and defeat devices for nonroad vehicles, engines, and equipment. Historically, DOJ and EPA have investigated and prosecuted such conduct, with the facts and circumstances of the violation determining the nature of the action (i.e., administrative, civil, or criminal).

Civil or Administrative Enforcement

For years, EPA and DOJ have maintained a robust CAA vehicle and engine enforcement portfolio, addressing myriad forms of noncompliance across supply chains and users. That portfolio has included, among other things, the manufacture or sale (including importation) of nonconforming engines or parts; distribution of aftermarket defeat devices; and emissions control tampering through the use of software and altering or “deleting” hardware components. Since 2016, the vast majority of CAA tampering, defeat device, and related cases have been brought administratively by EPA or through civil enforcement by DOJ with EPA’s support. In that time, the government has imposed hundreds of millions of dollars in civil penalties across hundreds of cases, not including some of the largest settlements against major automobile manufacturers.

EPA upped its enforcement efforts by selecting aftermarket defeat devices as a National Enforcement and Compliance Initiative (NECI) for FY2020 through FY2023. NECIs represent the agency’s top enforcement priorities and receive additional resources during the four-year cycle for which they are selected. During this NECI, EPA finalized 189 defeat device cases, totaling over $61 million in penalties. Criminal enforcement was a small part of EPA’s initiative, accounting for about 9% of total cases (17 criminal cases) and about 9% of total penalties ($5.6 million). The criminal cases also totaled $1.2 million in restitution, $438,000 in environmental projects, and 54 months of incarceration. In comparison, EPA concluded 172 civil enforcement cases, resulting in civil penalties totaling $55.5 million. This data makes clear that the vast majority of motor vehicle enforcement cases by EPA and DOJ have historically been administrative or civil-judicial.

Implications for Regulated Entities

Like OECA’s “Compliance First” policy, the decision not to criminally prosecute motor vehicle tampering cases marks an important and notable shift in DOJ’s (and EPA’s) enforcement approach. Regulated entities must realize, however, that changes in enforcement policy do not change the underlying law or regulations. Entities remain obligated to comply with all applicable laws and regulations.

Further, there are several important caveats to this new policy. First, the risk of criminal enforcement may currently be removed, but the policy could be amended, supplemented, or revoked entirely once the current administration ends. With a five-year statute of limitations under the CAA, violations committed during this administration could be prosecuted by a successor administration. Moreover, DOJ has signaled its intent to continue civil enforcement, and, if past is prelude, administrative and civil-judicial enforcement may remain a significant emphasis for EPA and a risk for those who choose to flout the law. While DOJ staffing reductions and a decrease in civil referrals from EPA may have caused a decrease in civil-judicial matters in 2025, it is simply too early to tell how this may relate to enforcement work and trends over the next three years. And, even if the likelihood of enforcement action is lower now than it was previously, the potential financial consequences of noncompliance could still be severe.

Second, the policy has limits, as exhibited in at least two cases. Less than one month after DOJ’s announcement, the US Court of Appeals for the Eighth Circuit upheld a vehicle tampering conviction where (1) the defendant did not appeal the conviction on CAA grounds and (2) there were several other criminal charges unrelated to tampering. In a second case currently pending in the Eastern District of Washington, the original indictment included CAA tampering charges and charges related to the unlawful smuggling of goods into the United States. In that case, the government has not moved to dismiss the indictment but, according to a document filed by defense counsel in the case, instead intends to seek a new indictment. These two cases indicate that DOJ is willing to pursue prosecutions of tampering conduct when that conduct is combined with violations of another criminal statute.

Third, regulated entities should not ignore that many states also have prohibitions on tampering and aftermarket defeat devices, and many states currently are ramping up their enforcement efforts. It remains imperative to pay attention to internal compliance and to be prepared for inspections and other interactions with regulators, including federal and state regulators. Entities should ensure robust compliance programs are in place no matter where located and especially in states that have signaled increased enforcement efforts in the past year.