EPA 2027 NOx Rule: What Truck Buyers Should Know Before Ordering

The EPA's tougher NOx limit for heavy-duty engines is scheduled to start with model year 2027, but the rules around it were still unsettled in the latest trade coverage we could find, dated Nov. 5–6. The agency has proposed cutting the extended warranty requirement, delaying longer useful-life requirements and ending DEF derates on new equipment. If you are ordering a new truck, the final rule could change your price, your warranty and even which engine you can buy. If you are buying used, the proposal does not by itself change trucks already on the road.

That uncertainty is now showing up in the order books. Here is what is known, what is not, and how to plan around it.

What the 2027 rule requires and what EPA wants to change

The rule finalized under the previous administration cuts the NOx limit from 0.2 to 0.035 g/hp-hr, and it also set a 0.050 g limit at low load and 10.0 g at idle. It would extend the heavy-duty diesel emissions warranty to 10 years or 450,000 miles.

On July 14, 2026, EPA published its proposed amendments in the Federal Register. Comments closed Aug. 29. According to EPA's fact sheet and trade reporting, the proposal would:

• Keep the NOx limits and the 2027 start date. EPA says the proposal retains nearly 90% of the original rule's NOx reductions.
• Keep today's warranty periods. The emissions warranty would stay at 5 years or 100,000 miles instead of expanding.
• Delay longer useful-life requirements until model year 2030.
• Remove DEF-related derates and speed restrictions from newly manufactured highway engines and new nonroad engines and equipment, including agricultural machinery.
• Allow nonconformance penalties (NCPs). Manufacturers could temporarily sell engines that do not fully meet the standard if they pay a penalty.

EPA estimates $12 billion in total savings and up to $6,000 per new truck. None of this is law yet. As FleetOwner noted in late September, the proposed amendments have no legal effect until EPA publishes a final rule, and the original rule takes effect Jan. 1, 2027 if they are not finalized.

Why Class 8 orders dropped in October

FTR reported preliminary North American Class 8 net orders of 15,600 units in October, down 24% from September and 36% from a year earlier. That is nearly 50% below the 10-year October average of 31,089. ACT Research put the month at 13,500 units, down 45% year over year.

Carter Vieth of ACT Research said the lack of clarity around the EPA 2027 rules and costs has left manufacturers and fleets unable to plan for next year.

Demand has not disappeared. Year-to-date orders are still 278,201 units, up 74% from the same period in 2025, and FTR's Dan Moyer said replacement needs, tighter capacity and firmer freight rates continue to support demand. FTR also suggested some purchases may be deferred rather than canceled, and that fleet capital may shift toward trailers in the near term.

What a 2027 truck might cost

Estimates vary, and all of them depend on the final rule. Recent figures from CCJ:

• Fully compliant engine: an estimated $8,000 to $12,000 premium.
• Engine sold under an NCP: an estimated $6,000 to $7,000 per engine if the penalty is passed through to the buyer.

FleetOwner has also cited industry estimates of $10,000 to $15,000 per vehicle for compliant engines. Treat any of these as planning ranges, not quotes. FTR's Moyer has also pointed out that higher NCPs would narrow the cost advantage of current-generation engines, so the size of the final penalty matters.

The OEMs are not all taking the same path

FleetOwner's October survey of manufacturer plans shows real differences, which means the same model year could bring different engine technology depending on the badge:

• Daimler Truck North America (Freightliner, Western Star, Detroit) opposes the NCP pathway and says it will launch a fully compliant Detroit Gen 6 on Jan. 1, 2027.
• Paccar (Kenworth, Peterbilt) told regulators it could not meet the standard by 2027 because of an immature supply base, and CEO Preston Feight said it plans to keep selling the current product.
• Cummins told regulators it would rely on NCPs and banked credits while it ramps up production.
• International says its S13 Integrated Powertrain will be 2027 compliant, and it is taking orders for first-quarter 2027 production using the proposed flexibility.
• Volvo Group told regulators it could offer 2026 carryover configurations through NCPs where capacity permits, and Mack plans to deliver a fully compliant 35 mg engine at the end of the first quarter of 2027.

These plans could change. International, for one, says it is prepared to adjust if the final rule differs significantly from the proposal.

What this means for used truck buyers and sellers

The proposed DEF changes apply to newly manufactured engines and equipment. EPA is taking comment on whether new guidance should extend them to in-use engines, but until something is issued, do not assume a used truck's derate behavior will change. Ask for its software and service history, and check whether any EPA-related DEF updates have been applied.

Warranty is the other used-market question. Under the proposal, a 2027 truck bought new would not come with the longer emissions warranty that the original rule required. That matters if you were counting on it, including for a truck you might buy second-hand in a few years.

Avoid paying a premium based on a guess about the final rule. For a used truck, base your offer on condition, mileage, aftertreatment history and how it fits your freight. Our pre-purchase inspection checklist covers what to look for.

Questions to ask before you sign a new-truck order

• Is this engine fully compliant with the 0.035 g standard, or will it be sold under an NCP or credits?
• If the final rule differs from the proposal, can the price or the spec change? Is that in writing?
• What emissions warranty is included, and what does an extended plan cost?
• Who pays if an NCP amount is set higher than expected?
• What is the delivery slot, and what happens if it moves?

Construction and agricultural buyers should ask similar questions about DEF inducements on new nonroad equipment, since the proposal covers those too.

Key takeaways

• EPA's 2027 NOx limit remains scheduled, but the proposed changes to warranty, useful life, derates and NCPs were not reported as final as of early November.
• Class 8 orders fell sharply in October, with FTR at 15,600 units and ACT at 13,500, as buyers waited for clarity.
• Current estimates put compliant engines at an $8,000 to $12,000 premium and NCP engines at $6,000 to $7,000, pending the final rule.
• OEM strategies differ, so ask exactly which engine and compliance path you are buying.
• The proposed DEF derate changes target new equipment, not trucks already in service.

If you would rather skip the 2027 question for now, browse inventory of trucks available today.