The engine offset turns a Section 232 tariff rebate into a domestic content test, counted in castings and turbochargers

Two, and then four. Those numbers, rather than the 3.75 percent rate, carry the policy in the procedures the International Trade Administration published on July 29¹. The notice extends the Section 232 parts-tariff offset, until now available to companies that assemble cars and trucks in the United States, to companies that assemble engines here¹. An engine plant earns credit only for models built with at least two U.S.-originating core components, such as blocks, heads or turbochargers, and from the third program year only for models with four¹. What began in 2025 as temporary relief for vehicle assemblers caught by a tariff on their own imported parts has become, in the engine version, a test of how much of the product is made in the United States. The tariff stays where it is. The offset decides who pays it.

The instrument: a rebate written into a national security tariff

Section 232 of the Trade Expansion Act of 1962, enacted October 11, 1962, lets the President, after a Commerce finding that imports threaten to impair national security, decide “the nature and duration of the action” needed to “adjust the imports of the article and its derivatives”⁸. Proclamation 10908, issued March 26, 2025, used that power to place a 25 percent duty on imported automobiles from April 3, 2025, and on certain automobile parts from May 3, 2025¹. Proclamation 10984, signed October 17, 2025, added a 25 percent duty on medium- and heavy-duty vehicles and listed parts from November 1, 2025, with buses at 10 percent².

The offset is the instrument’s internal counterweight. Proclamation 10925 of April 29, 2025, let a company assembling cars in the United States claim an amount it could set against the parts duties it owed³. The rate is a piece of arithmetic printed in the proclamation itself: 3.75 percent “reflects the total duty that would be owed when a 25 percent duty is applied to parts accounting for 15 percent” of a vehicle’s value^2,3. Proclamation 10984 extended the same structure to truck assemblers and told the Secretary of Commerce to build “an equivalent” process for engine manufacturers, with “the same accrual percentage rate and United States assembly requirement”².

The limits are set by proclamation, not by statute. An offset may be used only by importers of record the manufacturer authorizes, only against Section 232 duties on vehicle parts, and never above the manufacturer’s liability on those parts^1,3. The Secretary may also publish a notice that prospectively bars offsets for particular products if they work against the national security finding². Commerce issued the engine procedures as a notice effective on publication; the only comment it invites concerns the paperwork burden¹.

How the engine offset works: periods, parts and valuation

The program runs on two clocks. Engines for medium- and heavy-duty vehicles accrue offsets in five annual periods, the first covering engines assembled from November 1, 2025, through October 31, 2026, and the last ending October 31, 2030¹. Automobile engines get four periods, starting May 1, 2026 and ending April 30, 2030¹. Commerce explains the later start: vehicle offsets for cars assembled between April 5, 2025 and May 1, 2026 already included the engine’s value, and crediting the engine plant for the same months “would inappropriately allow import adjustment offsets to accrue multiple times for the same engine”¹.

The eligibility test is the novelty. Commerce treats engine production that does not use a minimum number of U.S.-originating core components as a “limited production operation” excluded from the calculation¹. Core components are turbochargers, including superchargers, and five engine parts drawn from Table A.2 of the USMCA’s automotive rules of origin: heads, blocks, crankshafts, pistons and rods¹. The USMCA table lists seven engine components, adding crankcases and head subassemblies, so Commerce took a subset and added a part the agreement does not name⁷. A component is U.S.-originating if it is substantially transformed in the United States, meaning processing that changes its “form, appearance, nature, or character”¹. Blocks and heads also qualify if “all or substantially all machining” happened here, judged by comparing value added by U.S. and foreign machining, and applicants must say where the machining took place¹.

Valuation follows two paths. Vehicle makers that build their own engines must value them on the USMCA’s Chapter 4 net cost method and may not claim more engine value than they used under the vehicle program¹. Independent engine makers may use net cost or the forecast sale price to the vehicle maker¹. Aftertreatment systems count only if fitted at the engine plant, and not if their value already went into a vehicle claim¹.

The paperwork resembles the vehicle program’s: a production forecast by model and plant, aggregate engine value, an estimate of parts-tariff liability split between the manufacturer and its suppliers, a list of authorized importers with their allotments, and a certification that cites the false-statements statute, 18 U.S.C. 1001¹. Commerce sends approved amounts to CBP, which applies them at entry summary filing¹. Offsets carry forward until used but cannot be “traded, sold, or transferred”¹. If a plant builds fewer engines, or cheaper ones, than it forecast, Commerce may cut the next year’s amount¹.

Who gains from the engine offset, and who does not

The beneficiaries are U.S. engine plants and the suppliers they name as importers of record. The proclamation that created the offset allowed a manufacturer to list suppliers in its chain as authorized importers³, and the engine notice keeps the importer list¹. As a matter of arithmetic, a plant with $1 billion of qualifying engine output in a year would accrue $37.5 million in offset, usable only against parts duties actually owed.

Commerce has published no estimate of the total. Its paperwork filing for the whole offset program, covering cars, trucks and engines, assumes 50 respondents at 40 hours each, twice a year⁶. By Commerce’s own count, then, this is a program for a few dozen manufacturers rather than for the parts trade at large⁶.

The engine notice also interacts with a rule written for trucks. In May, Commerce declared heavy-duty truck assembly that uses an imported chassis, glider or engine a limited production operation, ineligible for the vehicle offset⁴. A Class 8 truck built around an imported engine earns its assembler nothing; the same truck built around a U.S. engine with enough domestic core parts can earn offsets at both plants, subject to the rule against counting engine value twice^1,4. The cost of the exclusions falls on assemblers whose engines, or whose engine castings, come from abroad.

The longer view: from a tapering bridge to a content rule

The offset was first designed to disappear. Proclamation 10925 set 3.75 percent for cars assembled through April 30, 2026, then 2.5 percent for the following year, a rate that reflects a 25 percent duty on parts making up 10 percent of a vehicle’s value rather than 15³. Commerce’s first procedures said no new amounts would be granted for cars assembled after April 30, 2027⁵. Six months later Proclamation 10984 replaced that schedule with a flat 3.75 percent through April 30, 2030, citing the “close connections and overlap between part suppliers” for cars and trucks². The bridge became a standing feature of the tariff.

The engine test borrows its parts list from the trade agreement but not its geography. Under the USMCA, a passenger vehicle or light truck is originating only if the parts in Table A.2 are themselves originating, a rule that credits content made anywhere in the region⁷. The offset counts only parts transformed or machined in the United States¹. A block cast and machined in Mexico can be originating under the agreement and still count for nothing toward a U.S. engine plant’s offset.

Two questions stay open. Commerce has said it will define limited production operations for cars and medium-duty vehicles at a later date, and has not decided whether bus production qualifies⁴. For engines the threshold is already scheduled: the four-component requirement applies from the third program year, which begins November 1, 2027 for truck engines and May 1, 2028 for automobile engines¹.