Still on the calendar
The EPA's low-NOx standard for heavy-duty engines is still set to start in January 2027. It cuts allowed NOx from 200 to 35 milligrams per horsepower-hour, a reduction of roughly 85–87%. The separate EPA greenhouse-gas (CO2) truck standards have been eliminated, but NHTSA fuel economy rules still apply to manufacturers.
What the EPA has proposed
In July 2026 the EPA proposed several amendments. None of them carry legal weight until a final rule is published.
- Warranty: keep 5 years / 100,000 miles instead of moving to 10 years / 450,000 miles.
- Useful life: push the longer requirement back from 2027 to 2030.
- DEF: drop DEF-related derates and speed limits, and require an audible warning chime by 2029.
- Sensors: allow urea quality sensors to be removed.
- Penalties (NCPs): let makers pay a per-engine fee to sell engines that miss the 35 mg limit. FleetOwner estimates these fees at $6,000–$7,000 per truck, versus about $10,000–$15,000 extra for a fully compliant engine.
Daimler Truck North America says its compliant Detroit Gen 6 powertrain enters production January 1, 2027.
Seeing a light on the dash? Snap it with DERATE and know if you can keep driving
What it means for you
- Today's derates still apply. A low-DEF or bad-DEF-quality code can still cut your power and speed. Fix the cause and don't ignore it.
- Buying a 2027 truck? Ask the dealer whether the engine is fully compliant or sold under a penalty, and what warranty it carries.
- Most 2026 build slots are already taken, so plan early.