The U.S. Department of Justice has ordered federal prosecutors to stop pursuing criminal cases tied to diesel emissions “defeat devices," but that doesn't mean heavy-duty truck owners and aftermarket shops should start making plans for "diesel delete" kits.

On the social media platform X on January 21, the DOJ Environment and Natural Resources Division announced that the department "is exercising its enforcement discretion to no longer pursue criminal charges under the Clean Air Act based on allegations of tampering with onboard diagnostic devices in motor vehicles."

CBS News reported that it had reviewed a memo from Deputy Attorney General Todd Blanche that told prosecutors to drop all pending criminal cases and halt new prosecutions related to tampering with emissions control software under the Clean Air Act. 

This Does Not Mean Emissions Tampering is Legal

The decision marks a sharp departure from enforcement priorities that, for nearly a decade, placed diesel emissions deletes squarely in the DOJ’s criminal crosshairs.

Importantly, the memo does not legalize emissions deletes, nor does it eliminate civil enforcement by the Environmental Protection Agency or state regulators. 

But it does remove the threat of federal criminal prosecution for cases centered on software-based emissions tampering, including many involving diesel particulate filter deletes and aftermarket tuners.

Allen Schaeffer, executive director of the Engine Technology Forum, told Heavy Duty Trucking in an email that this is an important distinction.

DOJ is committed to sound enforcement principles, efficient use of government resources, and avoiding overcriminalization of federal environmental law. In partnership with the @EPA, DOJ will still pursue civil enforcement for these violations when appropriate.

— DOJ Environment and Natural Resources Division (@DOJEnvironment) January 21, 2026

How Prevalent are Diesel Deletes in Heavy Duty Fleets?

Much of the attention to the "diesel delete" issue has focused on pickup trucks, and the EPA study on this practice is limited to Class 2b and Class 3 pickup trucks.

"I have seen other EPA enforcement commentary that suggests that …..'while tampering data is limited to HD pickup trucks, it is reasonable to believe that tampering exists across other vehicle, engine and equipment types,'" Schaeffer said, adding, "I would agree."

"It is hard to say at what level tampering might exist in commercial trucks," he said. "However, given the ready availability of aftermarket devices and published guides on the internet, it is reasonable to assume that it occurs at some level, with economics being the main motivation."

Schaeffer warned of other consequences for heavy-duty trucking fleets of ignoring the emissions regulations regarding tampering.

"The inability to sell a used truck that has been tampered with seems like a reasonable deterrent if nothing else is," he told HDT. "And we may see states step up their activity in this vacuum, 

"Also, I have heard anecdotally that insurers have some general questions that could trip up vehicle insurance if OEM systems have been tampered with."

A Pardon in a Heavy-Duty Emissions Tampering Case

The move follows President Trump's pardon last fall of Troy Lake, the owner of Elite Diesel Service Inc., who had pleaded guilty in 2024 to conspiring to violate the Clean Air Act by disabling the monitoring components of the emissions control systems on hundreds of heavy-duty commercial trucks. He was sentenced to one year and a day and ordered to pay a fine.

Eight co-conspirators located in seven different states had previously been sentenced for their role in the conspiracy.

Between 2017 and 2020, Elite and Lake instructed employees to disable the computerized on-board diagnostic systems on at least 344 heavy-duty commercial trucks. OBDs are required under the Clean Air Act to monitor emissions-control hardware on vehicles and make sure it's working properly.

Elite’s co-conspirators, companies that operated diesel truck garages or diesel truck fleets, had disabled the emissions control hardware on these trucks and hired Elite and Lake to manipulate the OBDs so that the OBDs would not detect the malfunctions. This violated the Clean Air Act’s prohibition against tampering with monitoring devices.

A Long-Running Flashpoint in Trucking

Since the EPA’s 2007–2010 clean diesel rules took effect, emissions systems such as diesel particulate filters, selective catalytic reduction, and onboard diagnostic software have often been a frustrating part of heavy-duty truck ownership.

For fleets and owner-operators, the systems have delivered real air-quality benefits but also introduced new costs, complexity, and downtime. 

Over the years, that tension fueled a black market for emissions delete kits, particularly among vocational operators and long-haul fleets running older equipment.These kits allow mechanics to deactivate a diesel particulate filter. 

A DPF delete kit contains an exhaust that physically replaces the existing DPF, and a "tuner," which is software that enables the system to bypass the sensors and allow the engine to operate without a DPF.

Federal enforcement intensified after the Volkswagen diesel scandal in 2017, with EPA and DOJ investigators increasingly targeting diesel trucks and aftermarket suppliers. Criminal cases followed. Some resulted in prison sentences for shop owners and six- and seven-figure fines for businesses accused of selling or installing defeat devices.

That era now appears to be ending.

DOJ Shifts Strategy on Emissions Cases

In explaining the policy change, Blanche wrote that the department is exercising enforcement discretion to ensure “consistent and fair prosecution” and better allocation of resources, according to CBS. 

CBS also reported that the Justice Department is using a legal argument that tampering with emissions-related software (specifically onboard diagnostic systems) may not meet the Clean Air Act’s threshold for criminal liability, even if it remains a civil violation. The argument that OBD software is not "required to be maintained" under the Clean Air Act. 

Republican lawmakers, particularly from rural states, have long argued that such prosecutions unfairly targeted small businesses and tradespeople rather than large-scale polluters.

What It Means for Fleets and Shops

For trucking fleets, repair facilities, and technicians, the change lowers — but does not eliminate — the risk when deleting diesel emission systems on vehicles.

Emissions deletes and tampering are still illegal under federal law. 

Civil penalties can still reach tens of thousands of dollars per vehicle, and warranties can still be voided. And it's worth noting that state enforcement, especially in California and other CARB-aligned states, remains aggressive. 

EPA civil investigations are also unaffected by the DOJ memo.

What changes is the criminal exposure. Shop owners and technicians accused of software-based emissions tampering are far less likely to face federal indictments, prison sentences, or criminal records tied to Clean Air Act violations.

That distinction matters in a service environment already strained by technician shortages, rising repair costs, and increasingly complex powertrains. 

According to industry analysts, fear of criminal liability has had a chilling effect on some repair operations, even when dealing with used trucks that arrive already modified.

Uncertainty Remains 

Not everyone agrees with the DOJ’s legal reasoning. 

EPA attorneys have warned internally that emissions software must be maintained under the Clean Air Act and that weakening criminal enforcement could undermine long-term compliance.

Environmental advocates also point to EPA estimates that more than 550,000 diesel trucks had their emissions controls removed over the past decade, contributing hundreds of thousands of tons of excess nitrogen oxide emissions.

Editor's Note: This story was updated at 6:50 p.m. Eastern time to add comments from Allen Schaeffer.