EPA Relaxes Diesel Exhaust Fluid Rules for trucks. Cool, but really?

New rules have been rolled out by EPA to prevent sudden speed and power losses in diesel-powered trucks and farm equipment caused by Diesel Exhaust Fluid system failures—also known as DEF.

“This was one of the top issues discussed by farmers and ranchers at a round table I attended and Guyton, Georgia in May, and one I continue to hear about in my travels throughout the United States,” says Lee Zeldin, EPA Administrator, who announced the new rules on Tuesday.

“For farmers, truckers, and diesel vehicles operators, they’ve had to incorporate power loss and other issues caused by selective catalytic reduction systems that use DEF into their everyday life,” says Zeldin. “When DEF runs out, or if a sensor fails, vehicles are programmed to automatically lose significant speed and power leaving farmers stranded during harvest season and truckers stock while transporting America is goods.”

The EPA is now allowing manufacturers to revise the DEF system software on existing vehicles to prevent immediate severe slowdowns.

“The frustration with DEF has been nearly universal,” says Zeldin. “These modifications provide more flexibility and reliability without compromising air quality or emissions reductions.”

Starting with model year 2027, EPA requirements state that all new diesel on-road trucks must be engineered to avoid sudden and severe power loss after running out of DEF. To fix the problem for vehicles already in use, EPA’s new guidance now allows the necessary software changes to be made on the existing fleet. In addition to providing certainty to manufacturers about how EPA wants this issue resolved, the agency is not requiring separate approvals beyond that provided in EPA’s guidance.