EPA turns up the heat on truck emission rules

The Environmental Protection Agency hit the ground running in 2026, taking a sledgehammer to truck emission rules, including diesel exhaust fluid (DEF) and California regulations.

When it comes to truck emission standards, drivers will probably bring up two things to complain about: DEF and California. The EPA heard those complaints and is taking action.

Within one week, the EPA gutted California’s Clean Truck Check rules and teed itself up to do the same to the latest DEF regulations. It’s not as cut-and-dried as it sounds. Here’s everything you need to know.

Clean Truck Check can’t cross the state line

For several years, trucks with a 2009 or older engine have not been allowed inside California … until now … maybe.

California’s heavy-duty vehicle inspection and maintenance (HD I/M) regulation requires trucks over 14,000 pounds to pass an emission test. That test essentially disqualifies any engine that doesn’t have a DEF system. Better known as Clean Truck Check, the program applies to any truck operating in the state, including those registered outside the state.

By applying the rules to out-of-state trucks, Clean Truck Check turned more into a national regulation than a state regulation. At least for anyone wanting to do business in the Golden State. That could all change.

In January, the EPA issued a final rule disapproving of Clean Truck Check’s requirements on out-of-state trucks. Effectively, any truck – no matter what is underneath the hood or coming out of the tailpipe – can operate in California.

“The Trump EPA will never back down from holding California accountable and stopping them from imposing unnecessary regulations on the entire nation,” EPA Administrator Lee Zeldin said in a statement. “If California had its way, prices would skyrocket for truckers and businesses across America. Affordable trucks are vital for keeping food and goods moving and prices low for families. Americans didn’t vote for California’s policies to be imposed nationwide. They voted for President Trump’s policies that put working families first.”

Before carriers who normally stray away from California start doing business on the West Coast, the California Air Resources Board shot back with a message to the EPA: stay in your lane. In a statement to Land Line, CARB said it will continue to apply the program to all trucks, including those registered out of state.

“This announcement is a whole lot of bluster about bean counting,” a CARB spokesperson said in a statement. “EPA has no authority over this program, and we will continue to enforce the law to ensure that all trucks coming into and operating in California abide by the same rules — even if EPA doesn’t want to give us credit.”

As of early February, it is unclear how this will shakeout. While the feds are claiming authority, it appears California is continuing business as usual. That can open up drivers with older engines to state civil penalties.

Keep up with the progress in real time at LandLine.Media.

EPA vs. DEF

Last August, the EPA told engine and truck manufacturers to relax DEF derating schedules for current vehicles. The agency now has its sights set on future trucks.

Since 2010, new trucks have been required to be equipped with DEF systems in order to meet new emission standards. Manufacturers installed a very strict derate schedule to ensure compliance. Those schedules were loosened at the EPA’s request last year.

However, that DEF relief applied only to 2026 or older trucks. A 2022 heavy-duty NOx rule set new requirements for model year 2027 and newer trucks. In February, just a week after the EPA took a swing at California’s Clean Truck Check, the agency went after DEF rules for trucks of the future.

The EPA is demanding that manufacturers turn over information on DEF system failures. Essentially, the agency wants the evidence it needs to end DEF deratements “permanently” and “entirely.”

“As part of that regulatory process to hopefully be able to PERMANENTLY eliminate the deratements ENTIRELY, I am sending a mandatory data collection request today to manufacturers regarding DEF system failures to quickly evaluate ongoing issues independently and launch the next step Americans are DEMANDING,” Zeldin said in a social media post. “On behalf of our nation’s truckers, farmers and others, WE ARE GOING TO GET THIS DONE at TRUMP SPEED!”

OOIDA applauded EPA’s recent moves.

“On the heels of EPA’s final rule last week restricting CARB’s authority on trucks registered outside of California, OOIDA applauds the agency’s willingness to give truckers more flexibility when dealing with faulty emissions systems,” OOIDA President Todd Spencer said. “We believe the forthcoming data from engine manufacturers will once again prove that problems with nonsensical DEF regulations have sidelined small-business truckers for too long. We look forward to continued engagement with Administrator Zeldin and his staff to implement additional emissions solutions that better reflect the realities of trucking.”

This won’t eliminate DEF itself, but it will alleviate many of the headaches associated with the technology. LL