Cummins is rolling out updated engine calibrations that give truck operators more time to address diesel exhaust fluid (DEF) system issues before engine derates occur, following revised guidance from the U.S. Environmental Protection Agency.

The updates apply to more than 1.5 million medium- and heavy-duty engines, including certain truck applications dating back to the 2017 model year.

For heavy-duty truck and tractor engines, the revised calibrations extend the time before initial and subsequent derate events for certain DEF quality and tampering conditions. They also increase the final inducement speed from 5 mph (8 km/h) to 25 mph (40 km/h), allowing trucks to continue operating at more practical speeds while repairs are arranged.

The changes do not affect DEF-level inducements triggered by a low DEF tank, and operators must still comply with emissions requirements.

Cummins said the revisions follow updated EPA guidance intended to address customer concerns about unnecessary downtime while maintaining emissions compliance.

“We appreciate EPA’s engagement with industry stakeholders and view the revised guidance as an important step toward addressing customer concerns in a practical, compliance-focused way,” said Brett Merritt, vice president of Cummins’ Engine Business. “Cummins has acted to support reliable implementation of these updates, help customers and operators reduce unnecessary downtime, and continue to meet emissions requirements.”

Cummins said customers with eligible engines can contact their local dealer or distributor to schedule the calibration update as it becomes available for their specific engine platform and model year.