EPA's Changes to DEF Rules for Tractors

This article was originally posted at 3:24 p.m. CDT on Monday, March 30. It was updated with additional information at 3:48 p.m. CDT on Monday, March 30.

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OMAHA (DTN) -- Farmers frustrated with diesel exhaust fluid (DEF) shutdowns may see fewer breakdowns under new EPA guidance, though the agency's new guidance on DEF stopped short of eliminating the emissions systems altogether.

EPA did not eliminate the DEF rules, which have been a problem for farmers because of failure rates, but issued new guidance last week, giving major machinery manufacturers more flexibility in how they monitor exhaust emissions. EPA will now allow equipment manufacturers to use nitrous oxide (NOx) sensors to reduce problems with tractors and semi-trucks "de-rating" during operations.

Farmers will also have more opportunities to make repairs on the DEF sensors under EPA's guidance.

TRUMP COMPLAINTS ABOUT DEF

Speaking to farmers at a White House celebration on Friday, President Donald Trump called DEF restrictions "ridiculous," saying he would only buy older equipment for golf courses that didn't have them.

"Do you know about that? It was a basic disaster. Today, we're announcing new guidelines, drastically limiting these ridiculous DEF rules, saving farmers and consumers billions and billions of dollars," Trump said.

Trump said EPA's move also would significantly lower costs for farmers, or he would come after the equipment manufacturers.

"Because they're going to be able to very shortly produce a bigger, better tractor at substantially less money. It's going to be better. It's going to be a better tractor at substantially less money."

Trump also said the tractors will be more reliable. "It's not going to be turning off every 15 seconds because the computer went haywire," he said.

The Small Business Administration claims the EPA changes will save farmers $4.4 billion a year in repairs and lost productivity, though last August, SBA stated the regulatory change would save farmers $727 million per year in downtime and repairs. SBA also stated the change would provide nearly $13.8 billion in savings nationally.

SPELLING OUT THE SPECIFICS

Since 2013, EPA has required diesel engines to have selective catalytic reduction (SCR) emission controls and required DEF as the fluid that makes SCR work to reduce nitrous oxide emissions.

To comply, most manufacturers began installing urea quality sensors, which have become a major source for failures, leading to engine stalls and derating of power and shutdowns. Groups such as the Truck and Engine Manufacturers Association have identified the urea quality sensors as having among the highest failure rates of any equipment used in emission controls.

EPA stated a preliminary review of warranty data suggests that DEF sensor failures are a significant source of warranty claims. "Farmers and truck drivers should not have their vehicles stop working because a sensor isn't working properly," EPA stated.

Under the new guidance, manufacturers can reduce or end DEF sensor failures by removing urea quality sensors and replacing them with NOx sensors. EPA will also allow NOx sensors to be installed on existing engines without it being considered illegal tampering.

Patrick Kelly, vice president of energy and environmental affairs for the American Trucking Association, said EPA offered a pragmatic solution by allowing more flexibility on DEF monitoring to prevent forced shutdowns.

"As we have previously said, these systems have too often sidelined otherwise safe, compliant trucks due to faulty or unreliable DEF quality sensors, an issue that was compounded by widespread parts shortages in recent years," Kelly said. "When a bad sensor can trigger a full inducement, the result is unnecessary downtime, unnecessary towing costs, strained supply chains, and higher costs across the board."

EPA RULES GOING FORWARD

In August 2025, the Trump administration announced new guidance that allows farmers and truckers to revise software to prevent sudden speed and power losses caused by DEF system faults.

Starting with model year 2027, that guidance requires all new diesel on-road trucks to be engineered to avoid sudden and severe power loss after running out of DEF.

DEF ISSUES PERVASIVE

At an event in mid-March, Nebraska Farm Bureau President Mark McHargue asked farmers if they had had tractor or combine problems with system failures over diesel exhaust fluid (DEF) -- a federal emissions requirement that forces the engine to slow down if pollution controls aren't working. About half the crowd raised their hands.

McHargue said the DEF issue started coming up more frequently when the Nebraska Farm Bureau began holding conversations over right-to-repair legislation.

Newer equipment has gotten better at reducing engine failures, but there are increasing problems with used equipment over the past five to 15 years, McHargue said. "When you look at equipment sales, there is a premium for pre-DEF equipment, both in trucks and the tractors and combines, so there's something there," McHargue said.

He added, "From a farm practicality standpoint, that's just kind of a big deal that if we can get something to mitigate some of those problems."

WHAT IT MEANS FOR FARMERS

EPA is now saying farmers can restart their equipment if it has a DEF issue. In the past, EPA rules often required that if a farmer had a deratement issue, they would need to have the original equipment dealer come out and reset the machine.

That fix could still come with a cost, such as an annual licensing fee. For instance, a farmer still might need a software update on their equipment to allow them to repair it themselves. Companies such as Deere & Co. have software updates with their John Deere Operations Center Pro Service, so a farmer can fix it and not have to wait for the dealer. That Pro Service, however, requires an annual licensing fee.

MORE TO COME

DTN reached out to equipment manufacturers and the Association of Equipment Manufacturers to see how the new guidance would work for farmers.

AGCO responded that the company "welcomes any farm-friendly policies that provide greater clarity and help reduce costs for farmers -- a goal we fully share."

"When it comes to diesel emissions guidelines, any changes to regulatory requirements take time to engineer responsibly," AGCO stated. "We are committed to working constructively with the administration to deliver meaningful savings while ensuring farmers continue to have access to dependable, high-performing equipment."

Also see "EPA Investigates DEF Failures in Diesel Trucks, Seeks Data From Manufacturers" here: https://www.dtnpf.com/….

Chris Clayton can be reached at Chris.Clayton@dtn.com

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