Farmers could disable diesel exhaust fluid systems under House-passed bill

A farmer harvests corn beside Highway 163. (Photo by Cami Koons/Iowa Capital Dispatch)

by Cami Koons, Iowa Capital Dispatch
March 2, 2026

The Iowa House advanced a bill Monday that would allow farmers to disable the diesel exhaust fluid, or DEF, systems required by federal emissions laws.

House File 2529 would require manufacturers of farm equipment with DEF systems to provide diagnostic and repair information as well as software regarding the repair of a DEF system, so that farmers don’t have to rely on authorized technicians to fix a stalled machine.

Rep. Derek Wulf, R-Hudson, said the proposed legislation is a “farmer affordability bill” that allows producers to “repair and alter their equipment” and “remove the diesel emission systems if they so choose.”

The federal Clean Air Act requires most on-road and off-road diesel engines to have diesel exhaust fluid and systems that cause the engines to “de-rate” or slow down drastically when the fluid runs out. Wulf called the DEF systems, which help to limit the emissions of nitrogen oxides from the diesel engines, a “costly and burdensome” requirement from previous administrations. The regulation was implemented in 2010, but the U.S. Environmental Protection Agency under the Trump administration is working to modify the required derating principles.

“We have to do everything we can to help reduce additional costs to farmers who have to pay the penalty with their livelihoods because of environmentalist interests,” Wulf said.

In a subcommittee hearing on the bill, a lobbyist from Deere & Co., which registered against the bill, said providing parts and tools to individual operators would put manufacturers in competition with their own dealers who pay for that equipment and training.

Deere & Co. also pointed out that EPA recently issued guidance, at the company’s request, explaining that the Clean Air Act is not meant to interfere with equipment repairs.

Per the EPA guidance, manufacturers can disable the emission systems to allow a farmer to repair their equipment.

Rep. Kenan Judge, D-Waukee, said the bill seems to him more like a “right to modify” bill than a “right to repair” bill since it would allow farmers to disable the DEF systems on their equipment. He argued this would put Iowa and the attorney general “at odds with federal law.”

Judge said disabling the system would have “cascading effects” on the rest of the engine, would back dealers “in a corner” and harm farmers’ ability to use their machine warranties.

“I think it’d be more reasonable to try to advocate for our Congress and president of the United States to change this,” Judge said.

Wulf said that as the “ag-industry leader state in this nation,” Iowa should allow farmers to continue to be innovators.

“It’s time that we as a legislative body, once again, stand up for the American farmer and not the others who make money off the backs of the farmer and rancher,” Wulf said.

The bill advanced with a vote of 57-33, with mostly Democrats voting no. Democratic Reps. Josh Turek, J.D. Scholten and Austin Baeth voted in favor of the bill.  Ten Republican representatives voted against the measure.

Shellfish in Iowa

The House also advanced a bill that would create a new category for shellfish producers in Iowa’s animal feeding operations code.

Iowa code currently defines animals in a feeding operation as: cattle, swine, horses, sheep, chickens, turkeys or fish. House File 2534 adds shellfish to the definition at the request of the Iowa Department of Natural Resources and Iowa Soybean Association, according to Rep. Matt Windschitl, R-Missouri Valley.

“I just want to promise the body, there’s nothing fishy about the bill,” Windschitl said.

The bill specifies that one animal unit of shellfish is equivalent to 1,000 shellfish that individually weigh 25 grams or more, or 16,667 shellfish that weigh less than 25 grams.

HF 2534 advanced with a unanimous vote.

This article has been updated to clarify testimony from Deere & Company representatives.

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