Trump EPA weakens DEF derates
Key takeaways
- Manufacturers' required DEF derates will soon be less severe.
- Current equipment may enter limp mode and slow to 5 mph, or stop altogether until a DEF fault is cleared.
- The EPA's new guidance for MY2027 engines allows up to 650 miles or 10 hours of operation without performance changes after a DEF fault, and derates after that milestone are much less severe.
The U.S. Environmental Protection Agency (EPA) is lessening the consequences of diesel exhaust fluid issues.
Current diesel engine regulations require DEF-related faults to cause equipment to enter limp mode and slow to 5 mph or stop altogether. The EPA is now working to reduce the severity of those regulations.
The agency announced it issued new guidance to manufacturers of MY2027 diesel engines “that all new diesel on-road trucks must be engineered to avoid sudden and severe power loss after running out of DEF."
The new DEF derate guidance implements a tiered loss of power. Heavy-duty truck engines with a fault will experience: no performance changes for up to 650 miles or 10 hours; a mild derate after 4,200 miles or 80 hours; and then, finally, a 25 mph limit after 8,400 miles or 160 hours.