Cummins Delays Launch of 2027 X15 Diesel Engine
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Cummins will delay the launch of its latest X15 diesel engine for the heavy-duty on-highway truck market until late 2026, citing ongoing uncertainty around the introduction of federal tailpipe regulations.
Columbus, Ind.-based Cummins unveiled the , highlighting its compliance with U.S. Environmental Protection Agency and California Air Resources Board 2027-aligned regulations at launch.
Cummins said the engine would be available for pre-order in mid-2025 and deliveries would begin in 2026. The engine’s first showcase was at American Trucking Associations’ Technology & Maintenance Council’s 2025 annual meeting in Nashville, Tenn.
Days later, the Trump administration warned EPA regulations for heavy-duty trucks would be reassessed, with rollback likely.
The brightest spotlight would be placed on the Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles rules as well as the Heavy-Duty Nitrogen Oxide rule, said EPA Administrator Lee Zeldin.
Uncertainty prevailed for a number of months, with trucking stakeholders plus truck and engine manufacturers seeking clarity, until in late July EPA unveiled plans to scrap its authority to regulate greenhouse gases, including emissions from truck exhausts, which would nix the regulations.
Late 2026 Launch Now Expected
As a result, Cummins is delaying the 2027 X15 diesel engine launch, CEO Jennifer Rumsey told analysts and investors during the company’s second-quarter 2025 earnings call.
“So the regulations are still in place today. We’re continuing to work towards launching” the engine, Rumsey said. “We are no longer launching the X15 earlier in the year. So at the end of next year, we’ll be launching those new platforms to comply with the ’27 regulation.”
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Cummins still expects there to be NOx regulations. There may even be a belated pre-buy as a result, but when truck demand will pick up again is hazy, Rumsey said. A rush among fleets to “pre-buy” new trucks was anticipated before the stricter federal emission standards were due to take effect.
With the uncertainty, fleets have kept their pocketbooks closed. In Q2, for instance, Cummins’ heavy-duty engine sales in North America decreased 29% year over year to 22,000, and executives expect the third quarter to be much worse.
“We still believe today that we’ll have ’27 NOx regulation, and if we do, then that will likely drive demand back up, but it’s uncertain right now. We’re working closely with EPA to try to push for clarity and help them understand levers that they may have to reduce the total cost impact of that, in particular longer emissions warranty, but it’s really hard for me to predict,” the company’s top executive said.
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When the engine — part of Cummins’ High Efficiency, Lower emissions, Multiple fuels (HELM) program — does become available, it will have up to 605 horsepower and 2,050 pound-feet of torque.
A base engine, however, will still see an up to 4% improvement in fuel efficiency compared with the 2024 EPA X15 while maintaining similar diesel exhaust fluid consumption.
The newest version will feature fuel-saving technology, including revised coolant passages with lower flow resistance, decreasing water pump parasitics; a dual overhead camshaft layout that enhances breathing; a shorter piston with a longer connecting rod that lowers internal friction; and a revamped combustion system, the company previously told Transport Topics.
X15N First HELM Engine to Begin Production
The X15N, a natural gas variant of the X15 platform, was the first engine among Cummins’ HELM platforms to be made available to customers. Production started in July 2024. The HELM platforms include the B, X10 and X15 engines.
In March, Cummins unveiled the X10 engine platform and a B-Series engine update. The X10 platform is set to replace both L9 and X12 engines in 2027, and, like the X15, will be available with a variety of fuel options.
Even the diesel X15 will be capable of using biodiesel blends up to 20% and renewable diesel blends up to 100%.
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Had Cummins introduced the diesel X15 on the original timeline, however, orders were not guaranteed to have recovered, Rumsey and Chief Financial Officer Mark Smith told analysts.
“We view current order levels as unsustainably low, but immediate catalysts for recovery are not yet clear. We have not yet felt the full impact from tariffs, and there is still uncertainty about duration and ongoing levels, which was highlighted again last week with the flurry of new announcements,” said Smith.
Still, profit at Cummins jumped in Q2 even as heavy- and medium-duty engine sales tumbled.
Cummins reported net income of $890 million in the most recent three-month period, a 22.6% increase compared with $726 million in Q2 2024, benefiting from data centers’ hunger for electricity.
