Sounds Like OBD-II Performance Tuners Aren't Illegal Anymore

The Department of Justice says it will no longer seek criminal charges tied specifically to tampering with a vehicle’s onboard diagnostics system.

The announcement is effectively an about-face in how the government will approach enforcing action against the automotive aftermarket, after years of overzealous enforcement under the Clean Air Act.

The DOJ’s statement suggests that criminal prosecution for OBD-related violations will no longer be part of its enforcement toolbox. Industry advocates and enthusiasts have long argued that penalties were disproportionate to the actual crime, but the federal government was adament that OBD tampering undermined the entire emissions compliance framework—until now.

The newly announced enforcement discretion follows years of aggressive enforcement—including jail time and seven-figure criminal fines—aimed at shops and manufacturers accused of selling “off-road-use only” components that violate the Clean Air Act.

The decision is especially relevant to the diesel aftermarket, where emissions-related modifications have been most common. Owners of heavy-duty pickups have long moaned about diesel particulate filters and exhaust gas recirculation systems for robbing their trucks of performance, fuel economy, and long-term durability.

The DOJ’s announcement, made on social media, leaves key details unresolved. It suggests that existing criminal cases based solely on OBD tampering may be dropped or paused, though the department stopped short of clearly saying how ongoing prosecutions will be handled.

However, civil enforcement under the Clean Air Act will remain fully powered. Companies or individuals accused of violating emissions rules can still face substantial financial penalties, similar to the $1.7 billion civil settlement Cummins reached in 2024 over alleged defeat devices in its diesel engines. But it's not just diesel enthusiasts—remember when COBB Tuning agreed to a $2.9 million civil penalty for selling 90,000 "defeat devices" which were simply plug-and-play OBD performance tuners.

Do keep in mind that the DOJ did not signal any easing around removing or bypassing physical emissions hardware such as DPFs or EGR systems. Physically modifying those systems still remains illegal under federal law.

SEMA president and CEO Mike Spagnola acknowledged the distinction, welcoming the end of criminal penalties for OBD-related violations while reaffirming that emissions tampering itself is still prohibited.

“This is a welcome end to overly harsh penalties for violations that are otherwise addressed through civil enforcement. SEMA believes in following the law, and federal law is clear with regard to tampering of emissions systems or profiting from the sales of products that enable such behavior," said SEMA president and CEO Mike Spagnola.

"SEMA remains committed to working with federal regulators at the U.S. Environmental Protection Agency to ensure our industry has a voice in the development of policies impacting compliance with federal and state laws with regard to emissions and safety, and creating a path for our industry to continue its innovation.”

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