Cummins and Paccar Ease DEF Derates Following Updated EPA Guidance

Cummins and Paccar have announced adjustments to their diesel exhaust fluid (DEF) derate strategies in response to new guidance from the U.S. Environmental Protection Agency. The changes are expected to reduce the frequency and severity of power reductions that trucks experience when DEF levels run low or quality issues arise.

Under the revised approach, vehicles will provide more warning and allow additional miles before a derate is triggered, giving drivers more time to locate and refill DEF. The move aims to balance emissions compliance with operational practicality for fleets.

The EPA guidance clarifies how manufacturers can calibrate their systems while still meeting emissions standards. Cummins and Paccar are among the first to confirm they will update their engine software accordingly. Other manufacturers are expected to follow.