EPA updates DEF rules to prevent sudden power loss in diesel trucks and equipment

The U.S. Environmental Protection Agency is taking action to prevent diesel exhaust fluid issues from slowing down trucks on the road and farm equiment in the field. When a DEF-related fault occurs, equipment may enter limp mode and slow to 5 mph, or stop altogether until the fault is cleared.

New EPA guidance to manufacturers of MY2027 diesel engines require "that all new diesel on-road trucks must be engineered to avoid sudden and severe power loss after running out of DEF."

Additionally, when a fault is detected, the following will occur after the warning light illuminates:

No performance changes for up to 650 miles or 10 hours
Mild engine derate (15%) and no speed limiting for up to 4,200 miles or two work weeks
After about four work weeks, speed drops to 25 mph until repairs are made
Non-road equipment will not see any chages until a slight torque reduction after 36 hours.

EPA Administrator Lee Zeldin noted that DEF-related derates have been a major source of ire from the trucking and ag sectors.

“We have heard loud and clear from small businesses across the United States that the current DEF system is unacceptable," Zeldin said at the Iowa State Fair on Aug. 12. "It is unacceptable that farmers, truckers, construction workers, and many other small businesses continually experience failures of diesel-powered equipment when they need it most—costing millions of dollars in lost productivity.”

The move will also "increase the amount of time operators have to secure DEF and refuel while retaining the environmental benefits for farm equipment and trucks," he explained in an opinion piece for the ⁠Des Moines Register.

Zeldin also argued that the revised guidelines would lead to "fewer disruptions, reduced costs for emergency towing, repairs, rentals, DEF deliveries and inventories," which he estimated would farmers an estimated $727 million per year.

The sudden speed and power losses caused by DEF systems when DEF runs out were originally intended to prevent pollution and ensure compliance with EPA’s Tier 4 Emissions Standards, and can limit vehicles to as little as 5 mph within four hours of a DEF sensor alert.

As truckers know, sensor failures will trigger an automatic derate, which the EPA admitted "can be catastrophic...causing significant disruptions in logistics, agriculture,
and construction."

In 2021, the trucking industry learned this first-hand when a spate of bad NOx sensors led to recalls from Ford and Paccar.

Trucking industry response

After the EPA announcement, Owner-Operator Independent Drivers Association (OOIDA) President Todd Spencer stated:

"EPA’s guidance establishes more commonsense inducement schedules that will help drivers maintain safe control of their vehicles as they diagnose and remedy faulty DEF/SCR systems. More flexible inducement speeds and times will help truckers finish their trips, plan for necessary maintenance, and avoid parking their truck for an extended period simply because of a false alarm."

Spencer also added that previous inducement rules "sidelined small-business truckers for too long, and this accelerated relief shows what can be achieved when regulators hear directly from the people doing the job."

Patrick Kelly, American Trucking Associations' VP of energy and environmental affairs, praised the administration's response to industry concerns, stating that the solution reflects the realities of trucking.

“EPA’s new guidance will avoid unnecessary towing costs and equipment downtime while preserving the full environmental benefits that Selective Catalytic Reduction systems provide.”