Impact of DEF-Related Faults on Vehicle Operations
Vehicles often face severe restrictions, with speeds dropping to as low as five miles per hour due to DEF-related faults, disrupting logistics, agriculture, and construction activities.
Timeframe for Operator Response
According to existing regulations, when sensors in the SCR technology malfunction, vehicle operators must act within four hours; otherwise, a diesel engine can only operate at a maximum speed of five miles per hour before shutting down completely.
New EPA Guidance for Heavy-Duty Trucks
The new guidelines for heavy-duty trucks state that after a fault is identified, only a warning light will show for up to 650 miles or 10 hours. The EPA has noted that for at least one day, vehicle performance will remain unaffected.
Engine Derate Without Speed Limitation
Once the initial warning period passes, the guidance indicates that there will be a reduction in engine power by approximately 15%, yet speed restrictions will not be imposed. This allows trucks to function normally for up to 4,200 miles, roughly two weeks of additional work. After around four weeks, the speed will decrease to 25 miles per hour.
Concerns Over Compliance Strategies
The EPA acknowledged that the derate strategy, while meant to uphold Tier 4 emissions standards, has resulted in unnecessary frustration and delays, significantly impacting farmers, truckers, and equipment operators financially.
Feedback from the Business Community
Since 2010, most on-road diesel trucks and various non-road vehicles, including tractors and construction equipment, have implemented selective catalytic reduction systems that utilize DEF to minimize nitrous oxide emissions. EPA Administrator Lee Zeldin stated that small businesses across the country find the current DEF derate measures intolerable, emphasizing the substantial financial losses faced by those in agriculture and trucking.
Government Support for Reform
U.S. Secretary of Agriculture Brooke Rollins remarked that the alteration in DEF guidance helps alleviate government regulations that hinder farmers and ranchers, allowing them to spend more time in their fields rather than in repair shops.
For more information, Todd Neeley can be contacted at todd.neeley@dtn.com. You can also follow him on social platform X @DTNeeley.
(c) Copyright 2025 DTN, LLC. All rights reserved.
