EPA Vehicle Emission Compliance — Recalls, Warranties, and Import Rules

Federal vehicle emissions standards set the maximum allowable pollution from tailpipes — but the regulations at 40 CFR Part 85 are the enforcement machinery that makes those standards stick in the real world. Part 85 governs four key areas that affect vehicle owners, manufacturers, and importers: emission system warranty requirements (manufacturers must warrant their emission control systems for defined periods), vehicle recalls (EPA can order manufacturers to recall and fix vehicles that fail in-use emission testing), importation rules for vehicles not originally certified to U.S. standards, and exemptions for vehicles converted to run on clean alternative fuels. These rules implement Title II of the Clean Air Act (42 U.S.C. §§ 7521–7590), which governs all "mobile sources" — cars, trucks, motorcycles, and nonroad equipment.

Current Rule (2026)

What This Rule Does

The Clean Air Act requires EPA to set emission standards for new motor vehicles (42 U.S.C. § 7521) — standards for hydrocarbons, nitrogen oxides (NOx), carbon monoxide, and particulate matter that each new vehicle model must meet before EPA issues a certificate of conformity authorizing sale. 40 CFR Part 85 is the compliance side of that system: what happens after the certificate is issued.

Emission system warranties (Subpart V): Under 42 U.S.C. § 7541, manufacturers must warranty their emission control systems. For light-duty vehicles, the performance warranty covers 2 years/24,000 miles (whichever comes first) — if the vehicle fails an emissions inspection during that period due to a defective emission part, the manufacturer must repair it at no cost. The longer design and defect warranty covers 8 years/80,000 miles for major emission components (catalytic converter, electronic emission control unit, onboard diagnostic system), meaning manufacturers are liable for defects in these components for 8 years from date of first sale. Part 85 specifies how warranty claims work, what documentation manufacturers must provide, and how EPA enforces warranty obligations.

Emission defect reporting (Subpart T): If a manufacturer discovers — through internal testing, field reports, or otherwise — that a significant number of a class of vehicles have a defect that causes them to exceed emission standards, the manufacturer must report that defect to EPA within 15 business days. Reporting triggers EPA review and potentially a recall order. This is the mechanism that catches emission system failures discovered post-sale.

Recalls (Subpart S): When EPA finds, through in-use testing (testing vehicles from actual owners after sale), that a class of vehicles fails to conform to emission standards, EPA may order the manufacturer to recall and remedy those vehicles at no cost to owners. The recall process involves EPA issuing a formal notification, the manufacturer submitting a remedy plan, and EPA approving the plan. During the recall period, manufacturers must notify registered owners of the affected vehicles. The EPA recall authority was central to the 2015 Volkswagen "Dieselgate" enforcement action.

Vehicle importation (Subpart P): Vehicles sold in other countries are often not certified to U.S. emission standards. Subpart P governs how non-conforming vehicles can be legally imported — primarily through Independent Commercial Importers (ICIs), who are authorized to modify, test, and bring non-conforming vehicles into U.S. compliance. An ICI must hold an EPA certificate of conformity (or post a bond), modify the vehicle to meet U.S. standards, and test it before it can be released for sale. Tourists and temporary imports have separate exemptions. Individuals cannot simply import a non-conforming vehicle for permanent use without going through the ICI process.

Clean fuel exemptions (Subpart F): Vehicles converted to run on clean alternative fuels (natural gas, propane, electric) may be exempt from the tampering prohibition that otherwise bars modification of certified emission systems. The exemption requires the conversion to actually reduce emissions and use components that meet EPA performance standards.

Key Provisions

• § 85.1502 — Definitions for importation: "nonconforming vehicle" (not covered by a U.S. certificate of conformity); "independent commercial importer (ICI)" (importer authorized to bring non-conforming vehicles into compliance); "certificate holder" (OEM or authorized representative with U.S. certificate of conformity)
• § 85.1503 — Importation procedures: the importer must file CBP entry, obtain EPA conditional release, modify the vehicle to conform to applicable standards, test the vehicle using EPA-specified procedures, and submit documentation to EPA before the vehicle can be permanently released for use
• § 85.1507 — ICI bonding: ICIs must post a bond (typically equal to the estimated cost of remedy or potential fine) to cover the risk that a vehicle they import cannot be brought into compliance — the bond is forfeited and the vehicle must be exported or destroyed if compliance cannot be achieved
• § 85.1701–85.1714 — Recall regulations: EPA may order a recall if in-use testing reveals nonconformance; manufacturers must submit a recall plan including notification procedures, repair procedures, and timeline; EPA must approve the plan before the recall launches; recall repairs must be completed within 60 days of owner notification or within a timeframe EPA specifies
• § 85.1801–85.1809 — Emission defect reporting: manufacturers must report any defect affecting 25 or more vehicles/engines in a class if the defect causes emission exceedances; report must include vehicle identification, description of the defect, potential environmental impact, and the manufacturer's proposed remedy; the 15-business-day clock runs from when the manufacturer first determines a defect exists
• §§ 85.2101–85.2145 — Warranty: manufacturers must provide owners with a written warranty statement explaining coverage; covered repairs include replacement of any emission-related part that fails within the warranty period due to defect; warranty does not cover damage caused by misuse, improper maintenance, or tampering; manufacturers cannot deny warranty claims based solely on the installation of non-OEM parts unless EPA proves the non-OEM part caused the failure (Magnuson-Moss Warranty Act principle)
• §§ 85.2201–85.2230 — Voluntary aftermarket part certification (within Subpart V): an aftermarket parts manufacturer may seek EPA certification that its part will not cause a vehicle to exceed emission standards; certified aftermarket parts can be installed on warranty-covered vehicles without voiding the emission warranty

How It Affects You

If your vehicle fails an emissions inspection: If the vehicle is within the 2-year/24,000-mile performance warranty period and fails due to an emission system defect (not wear or abuse), the manufacturer's dealer must fix it at no charge. The warranty covers the catalytic converter and electronic emission control unit for 8 years/80,000 miles even if the shorter performance warranty has expired. Keep records of all emission-related repairs — they may be relevant to a warranty claim if problems recur.

If your vehicle is subject to an EPA recall: EPA recall notifications go to the registered owner (using DMV data) and are posted at recalls.gov. If your vehicle is recalled for an emission defect, the manufacturer must fix it at no cost. Unlike NHTSA safety recalls, EPA emission recalls do not carry the same public urgency — most vehicles recalled for emissions continue to drive safely — but outstanding emission recalls can affect resale value and, in some states, block registration renewal. You can check your VIN at recalls.gov for any outstanding emission recalls.

If you want to import a foreign-market vehicle: Vehicles manufactured for foreign markets (Japan-spec, European-spec) are often not certified to U.S. emission standards. If the vehicle is 25 years or older, it is exempt from emission standards and can be imported freely (the "25-year rule"). For newer vehicles, you must use a licensed ICI — the cost of conversion and testing typically runs $10,000–$50,000 depending on the vehicle's original configuration. A vehicle that cannot be brought into U.S. compliance cannot be permanently imported; the bond the ICI posted covers the cost of exporting or destroying it. EPA and CBP coordinate enforcement — CBP will not release a non-conforming vehicle without EPA authorization.

If you are a manufacturer facing an in-use recall: EPA's in-use testing program pulls vehicles from actual owners across the country and tests them on the Federal Test Procedure. If EPA's testing finds systematic nonconformance, the agency sends a Notice of Nonconformance before ordering a recall. Manufacturers typically contest the findings or negotiate remedy terms with EPA before the recall order issues. The Dieselgate case — in which Volkswagen's defeat device software enabled vehicles to pass EPA lab tests while exceeding limits on the road — was a rare case of intentional circumvention; more common recalls involve catalytic converter degradation, sensor failures, or software calibration drift.

Heavy-Duty Vehicle Emission Standards (40 CFR Part 1037)

While Part 85 covers the compliance machinery (recalls, warranties, imports), EPA's heavy-duty vehicle emission standards are set separately at 40 CFR Part 1037 — Control of Emissions from New Heavy-Duty Motor Vehicles. This Part governs trucks, buses, and other vehicles with a gross vehicle weight rating (GVWR) over 8,500 pounds — semi-trucks, transit buses, garbage trucks, delivery vans, and pickup trucks/SUVs over that threshold. Collectively, heavy-duty vehicles account for roughly 25% of U.S. transportation greenhouse gas emissions despite being far fewer in number than passenger cars.

Key provisions:

• §§ 1037.101–1037.145 — Emission standards (Subpart B): separate standards by vehicle category (heavy heavy-duty, medium heavy-duty, light heavy-duty), fuel type (diesel, gasoline, natural gas, propane), and regulatory subcategory (urban buses have stricter PM standards); NOx standards for heavy-duty diesel engines phase down from 0.2 g/bhp-hr (pre-2027) to 0.035 g/bhp-hr (MY 2031+) under the 2024 Clean Trucks final rule
• §§ 1037.201–1037.250 — Certifying vehicle families (Subpart C): manufacturers certify vehicle families — groups of vehicles with the same emission performance — rather than every individual unit; each family must have a valid certificate of conformity before production begins; the certificate specifies the engine family's FEL (Family Emission Limit)
• §§ 1037.301–1037.330 — Testing production vehicles (Subpart D): EPA conducts selective enforcement audits (SEA) of production vehicles from actual production lines; manufacturers must cooperate and provide production vehicles for testing; failing an SEA triggers a recall obligation
• §§ 1037.401 — In-use testing (Subpart E): EPA tests vehicles from actual fleets; heavy-duty in-use testing uses the Not-to-Exceed (NTE) zone concept — NOx emissions must not exceed NTE limits across a wide range of real-world operating conditions, not just during the formal test cycle
• §§ 1037.701–1037.745 — Averaging, Banking, and Trading (ABT, Subpart H): manufacturers may average emissions across a vehicle family (some vehicles can exceed limits if offset by others below the limit), bank credits from especially clean vehicles for future use, and trade credits with other manufacturers; ABT provides flexibility but total industry emissions cannot exceed total standards
• § 1037.135 — Zero-emission vehicle (ZEV) and near-zero emission vehicle (NZEV) provisions: the 2024 rule established an accelerating ZEV sales requirement for heavy-duty trucks, requiring manufacturers to sell specified fractions of zero-emission vehicles in their heavy-duty lineups — a parallel track to the NOx tightening

The heavy-duty certification and compliance system differs from light-duty in one key respect: engine families rather than vehicle models are the unit of certification. A diesel engine family certified by Cummins, Paccar, or Daimler can be installed in trucks from multiple vehicle manufacturers — so engine certification and vehicle certification are separate processes. Part 85's recall and warranty provisions apply to heavy-duty vehicles as well; the Clean Trucks rule updated Part 85 to incorporate the heavier-duty warranty terms (extended coverage periods and expanded component lists) required by the tighter MY 2027+ standards.

Marine Compression-Ignition Engine Emission Standards (40 CFR Part 1042)

EPA's marine diesel emission standards at 40 CFR Part 1042 — Control of Emissions from New and In-Use Marine Compression-Ignition Engines and Vessels — extend the federal emission control program to boat and ship engines. Marine diesel engines are significant sources of NOx, particulate matter (PM), and hydrocarbons in coastal and inland waterway communities. Part 1042 regulates three engine categories by power and application:

• Category 1 — smaller marine diesel engines (below 37 kW or meeting specified power density limits), typically found in small commercial vessels and large recreational boats
• Category 2 — medium marine diesel engines (37–2,000 kW), used in ferries, tugboats, workboats, and commercial fishing vessels
• Category 3 — the largest marine diesel engines (above 2,000 kW), used in ocean-going cargo ships and tankers; these engines also fall under the IMO MARPOL Annex VI international standards addressed at 40 CFR Part 1043

Emission standards (§§ 1042.101–1042.104): NOx, PM, hydrocarbon, and carbon monoxide limits apply by engine category and model year, tightening in tiers (Tier 1 through Tier 4). Tier 4 NOx standards for Category 1 and 2 engines (fully phased in for new engines) require an approximately 80–90% reduction compared to uncontrolled levels — typically achieved through selective catalytic reduction (SCR) with diesel exhaust fluid (DEF). Category 3 engines are governed by the IMO Tier III international NOx standard for vessels operating in Emission Control Areas (ECAs), including U.S. coastal waters.

Certification and compliance structure: Like the highway vehicle program, Part 1042 requires manufacturers to certify engine families before sale (§§ 1042.201–1042.250 — Subpart C). Each family is defined by engine characteristics that affect emissions; all engines within a family must comply with the certified standards. Production-line testing (Subpart D) allows EPA to audit production engines to verify they match the certified configuration. The averaging, banking, and trading (ABT) program (Subpart H) allows manufacturers to bank credits from over-complying engines and use them against future models — providing compliance flexibility similar to the highway sector's EPA credit system.

Key provisions:

• § 1042.101 — Exhaust emission standards for Category 1 and 2 engines: tiered NOx/PM/HC limits by power rating and model year
• § 1042.104 — Exhaust emission standards for Category 3 engines: large ship engines subject to IMO Tier III NOx standards in ECAs
• § 1042.110 — SCR reductant monitoring: engines with SCR systems must record reductant (DEF) use and trigger diagnostic alerts when reductant runs low
• § 1042.120 — Emission-related warranty: manufacturers must warrant that engines comply with emission standards for the lesser of 3 years or 3,000 hours for Category 1 engines; longer periods for Category 2 and 3
• § 1042.125 — Maintenance instructions: purchaser must receive written instructions for maintaining emission controls; instructions cannot require maintenance more frequently than necessary
• § 1042.130 — Installation instructions: engine manufacturers selling to vessel builders must provide installation instructions that prevent the installation from defeating emission controls
• § 1042.135 — Labeling: each engine must carry a permanent EPA compliance label showing the engine family, model year, and emission standards to which it was certified
• § 1042.145 — Interim provisions: transition rules for manufacturers during initial tier phase-in periods

Remanufactured marine engines (Subpart I): Unlike the highway program, Part 1042 includes explicit provisions for remanufactured marine engines — engines that undergo significant rebuilding. Remanufactured Category 3 engines operating in ECAs must meet emission standards upon remanufacture, bringing older engines into compliance when they undergo major overhaul.

Recent rulemakings: EPA finalized Tier 4 standards for Category 1 and 2 marine diesel engines (73 FR 37243, June 2008), effective for new engines in MY 2014–2017 depending on category. EPA subsequently updated requirements for SCR systems and onboard monitoring (81 FR 74153, October 2016; 86 FR 34512, June 2021). The most recent significant update (88 FR 4662, January 2023) addressed Category 3 vessel compliance in Emission Control Areas, aligning domestic requirements with IMO Tier III implementation.

Spark-Ignition Marine Engine Emission Standards (40 CFR Part 1045)

EPA's spark-ignition marine engine standards at 40 CFR Part 1045 — Control of Emissions from Spark-Ignition Propulsion Marine Engines and Vessels — cover the gasoline-powered outboard motors, personal watercraft (PWC), and sterndrive/inboard engines used in recreational and light commercial boating. Unlike marine diesel engines (addressed in Part 1042), spark-ignition marine engines emit primarily hydrocarbons (HC), carbon monoxide (CO), and NOx — and outboard and PWC engines are particularly significant HC sources because older two-stroke designs discharged a fraction of unburned fuel directly into the water during normal operation.

Exhaust emission standards (§§ 1045.101–1045.107):

• Outboard and PWC engines (§ 1045.103): Tier 3 standards apply to new outboard and personal watercraft engines — the most stringent requirements under Part 1045. HC+NOx combined limit of 30 g/kW-hr, with further tightening for higher-displacement engines. These standards drove the industry shift from carbureted two-strokes to direct-injection two-stroke and four-stroke technology.
• Sterndrive and inboard engines (§ 1045.105): Four-stroke sterndrive and inboard engines (stern-mounted or mid-ship, used in runabouts and cruisers) face separate HC+NOx limits. The standards are more lenient than outboard/PWC given the different combustion architecture, but still require modern emission control calibration.
• Not-to-exceed (NTE) standards (§ 1045.107): In addition to the test-cycle standards, engines must meet NTE limits across a defined range of real-world operating conditions — preventing manufacturers from optimizing for the test cycle while allowing excess emissions under other conditions.

Evaporative emission standards (§ 1045.112):

• Fuel tanks, fuel lines, and carburetor or fuel injection components on marine vessels must meet evaporative HC emission limits — separate from exhaust emissions
• Evaporative standards apply to the vessel (not just the engine) and include both diurnal emissions (from temperature cycling) and permeation through fuel lines and tanks
• These requirements have driven the transition to low-permeation fuel line materials and sealed fuel system designs in recreational boats

Emission-related warranty (§ 1045.120):

• Manufacturers must warrant their engines' compliance with emission standards for a minimum period based on engine category and anticipated hours of use
• Warranty coverage for spark-ignition marine engines is based on expected seasonal use patterns (hours, not years in many cases)

Certification and compliance structure:

• Engine families are certified by the manufacturer before sale (Subpart C); production engines must match the certified configuration
• The averaging, banking, and trading (ABT) program (Subpart H) allows manufacturers to meet fleet-average emission levels rather than per-engine compliance — credits from cleaner engines offset those that exceed the standard
• The selective enforcement audit (SEA) program (Subpart D) allows EPA to pull production engines from assembly lines and test them against certified specifications

Recent rulemakings: The foundational Part 1045 standards were finalized at 73 FR 59194 (October 2008), effective for model years 2010+ for most engine categories. The rule phased in requirements through 2011–2016 for different engine sizes. No major changes to exhaust standards since 2008; EPA has updated evaporative emission requirements and onboard diagnostic requirements through subsequent rulemakings.

Small Nonroad Spark-Ignition Engine Emission Standards (40 CFR Part 1054)

EPA's small nonroad spark-ignition engine standards at 40 CFR Part 1054 — Control of Emissions from New, Small Nonroad Spark-Ignition Engines and Equipment — cover the gasoline-powered engines used in outdoor power equipment: lawnmowers, string trimmers, chainsaws, leaf blowers, generators, pressure washers, and garden tillers. These engines (under approximately 19 kW / 25 hp) collectively contribute significantly to ground-level ozone formation and air toxics in residential areas because they typically run without catalytic converters and at high steady-state loads.

Engine categories and applicability (§ 1054.1):

• Handheld engines: engines in equipment operated while held by the operator — chainsaws, string trimmers, leaf blowers, cut-off saws, hedge trimmers; higher HC and CO emitters per hour because of throttling demands and two-stroke legacy technology
• Nonhandheld engines: engines in equipment that rests on the ground during operation — lawnmowers, tillers, generators, pressure washers, riding mowers; larger displacement, longer operating cycles, and more opportunity for four-stroke technology

Exhaust emission standards (§§ 1054.103, 1054.105):

• Handheld engines: HC+NOx combined standards in g/kW-hr, with a separate CO limit; two-stroke handheld engines must now meet the same standards as four-strokes, driving adoption of cleaner direct-injection two-stroke technology (§ 1054.103)
• Nonhandheld engines: HC+NOx and CO limits expressed per kW-hr; equipment under 225 cc displacement faces different standards than larger displacement equipment; useful life for nonhandheld engines is 250 hours (§ 1054.107)
• Useful life for handheld engines is 50 hours — the standards must be met over this period of operation (§ 1054.107)

Evaporative emission standards (§§ 1054.110, 1054.112):

• Fuel tanks, fuel lines, and carburetors on outdoor power equipment must meet diurnal evaporation and permeation limits — the HC that evaporates from fuel systems parked in garages contributes meaningfully to household VOC exposure and regional ozone
• Standards apply to the complete piece of equipment, not just the engine — equipment manufacturers must design compliant fuel systems regardless of engine certification status

Warranty and labeling requirements: Manufacturers must warrant emission system compliance for the useful life period (§ 1054.120) and provide maintenance instructions to buyers covering emission-related components (§ 1054.125); each engine must be labeled with a unique ID, EPA compliance statement, and emission family designation (§ 1054.135).

Recreational Vehicle Emission Standards (40 CFR Part 1051)

EPA's recreational vehicle emission standards at 40 CFR Part 1051 — Control of Emissions from Recreational Engines and Vehicles — cover a distinct category of nonroad equipment: snowmobiles, off-highway motorcycles (dirt bikes), and all-terrain vehicles (ATVs) and off-road utility vehicles (UTVs). These are consumer vehicles used in outdoor recreation that are generally not allowed on public roads and fall outside the on-highway vehicle emission framework of Title II.

Vehicle categories and exhaust standards:

• Snowmobiles (§ 1051.103): Exhaust standards applied by model year; HC+NOx limits that drove the shift from two-stroke carbureted engines (the dominant snowmobile technology for decades) to direct-injection two-strokes and four-strokes; snowmobiles are high HC emitters in cold-start and idling conditions that affect air quality in mountain resort communities
• Off-highway motorcycles (§ 1051.105): HC, CO, and NOx limits for dirt bikes and enduro motorcycles; standards are less stringent than on-highway motorcycle standards under 40 CFR Part 86 given the different use patterns (shorter duration, lower idle time)
• ATVs and UTVs (§ 1051.107): HC+NOx and CO standards for all-terrain vehicles and off-road utility vehicles (side-by-sides), which have grown into a major recreational and agricultural use market; larger displacement UTVs approaching light-duty vehicle power levels are regulated here rather than under highway standards

Consumer labeling (§ 1051.137): Every recreational vehicle certified under Part 1051 must be labeled with a removable hang-tag showing its emission characteristics relative to other models in the category — an unusual consumer disclosure requirement that allows buyers to compare the emission performance of competing snowmobiles, dirt bikes, or ATVs at the point of sale.

Evaporative standards (§ 1051.110): All vehicles using volatile liquid fuel must meet evaporative HC standards over a five-year useful life — covering both diurnal evaporation (temperature cycling in storage) and running losses; important for recreational vehicles that spend extended periods in storage.

Recent rulemakings: The foundational Part 1051 standards were finalized at 69 FR 2397 (January 2004), with phased model-year implementation. EPA has updated specific provisions through subsequent rulemakings but no comprehensive overhaul since 2004.

Nonroad Compression-Ignition (Diesel) Engine Emission Standards (40 CFR Part 1039)

Construction equipment, agricultural machinery, mining vehicles, industrial generators, and airport ground support equipment running on diesel engines are regulated under 40 CFR Part 1039 — Control of Emissions from New and In-Use Nonroad Compression-Ignition Engines (67 sections). These are the EPA standards for off-road diesel engines — the same type of engine as a highway truck's diesel but operating in equipment that never touches a public road. Part 1039 applies to engines from 8 kW (11 hp) upward, covering the excavators, bulldozers, combine harvesters, and large diesel generators that account for a significant share of U.S. NOx and PM emissions from the mobile source category.

The Tier 4 standards (fully phased in after the 2014 model year) drove the adoption of two critical technologies in nonroad diesel engines:

• § 1039.101 — Tier 4 exhaust standards: post-2014 Tier 4 Final standards require NOx ≤ 0.40 g/kW·hr and PM ≤ 0.025 g/kW·hr for most power categories — roughly an 85–95% reduction in NOx and PM from pre-Tier 4 levels; achieving these levels requires aftertreatment systems that did not exist in older equipment
• § 1039.110 — SCR diagnostic requirements: engines equipped with Selective Catalytic Reduction (SCR) systems — which inject diesel exhaust fluid (DEF, a urea-water solution) to chemically reduce NOx to nitrogen and water — must have onboard diagnostic systems that alert operators when DEF levels are low or the SCR catalyst is malfunctioning; EPA prohibits SCR-equipped engines from operating with a known fault without displaying a fault indicator
• § 1039.120 — Emission warranty: manufacturers must warrant emission-related components (fuel systems, SCR catalysts, diesel particulate filters, EGR systems) for the engine's useful life — typically 3,000 hours or 5 years for smaller engines, up to 8,000 hours or 10 years for large mining equipment
• § 1039.135 — Engine labeling: every engine must bear a permanent label showing the EPA certification tier level, displacement, power rating, and emission standards met; the label is the primary field-inspection tool for determining what standards the engine was certified to and whether it has been modified

DEF-enabled SCR became essentially mandatory for nonroad diesel after Tier 4, creating a new maintenance requirement for construction fleets: keeping DEF tanks filled. Running out of DEF causes derate — the engine automatically reduces power to motivate operators to refuel DEF — and repeated noncompliance can trigger complete engine shutdown in later designs.

Large Nonroad Spark-Ignition Engine Emission Standards (40 CFR Part 1048)

Forklifts, large generators, airport ground support vehicles (baggage tugs, belt loaders), and other industrial equipment powered by gasoline, propane, or natural gas engines above 19 kW fall under 40 CFR Part 1048 — Control of Emissions from New, Large Nonroad Spark-Ignition Engines (65 sections). These engines are the industrial counterpart to the small nonroad engines in Part 1054 (lawn equipment, chainsaws) — larger, commercial-duty engines running in warehouses, airport aprons, and industrial facilities:

• § 1048.101 — Exhaust emission standards: tiered emission standards for HC, CO, and NOx with increasingly tight limits; the current standards require three-way catalytic converters on most engines above 19 kW, achieving HC+NOx combined emissions similar to on-highway vehicles
• § 1048.110 — OBD requirements: engines equipped with three-way catalysts and closed-loop air-fuel control must have onboard diagnostic systems that monitor catalyst efficiency and air-fuel sensor function; a malfunction indicator light (MIL) must alert operators when the diagnostic system detects emission control degradation
• § 1048.140 — Blue Sky Series: EPA's voluntary "Blue Sky Series" designation recognizes engines that meet substantially more stringent emission limits than the mandatory standards; manufacturers may market Blue Sky Series engines as a premium environmental option; the designation requires third-party verification and carries no regulatory advantage, but allows purchasers (including government fleet buyers with clean equipment requirements) to identify superior-performing equipment

The large nonroad SI market is smaller than either the nonroad diesel or small SI markets, but fleet operators — particularly warehouse and distribution center operators with large indoor forklift fleets — are among the most affected. Indoor SI forklifts on propane or natural gas run in enclosed spaces where CO and NOx accumulate; the OSHA permissible exposure limits for CO (50 ppm as a 8-hour TWA) and the Part 1048 emission limits interact directly in OSHA workplace air quality compliance for forklift-intensive environments.

General Compliance Provisions Across All Nonroad Programs (40 CFR Part 1068)

While the Parts above (1037, 1039, 1042, 1045, 1051, 1054) set the emission standards for each engine category, 40 CFR Part 1068 — General Compliance Provisions for Highway, Stationary, and Nonroad Programs (73 sections) — is the unified enforcement rulebook that applies across all of them. Every manufacturer, importer, and equipment maker certified under any of the nonroad emission programs must comply with Part 1068:

• § 1068.101 — Prohibited acts: the four core prohibitions that apply to everyone — (1) selling or importing engines without a valid certificate of conformity; (2) installing, selling, or using a "defeat device" — any element that reduces emission control effectiveness under real-world conditions relative to the testing laboratory; (3) "tampering" — removing, disabling, or altering any emission control system after manufacture; (4) "misfueling" — using a fuel that a manufacturer prohibits because it would harm the emission controls; violations are subject to civil penalties up to $37,500 per engine per day
• § 1068.103 — Certificate of conformity duration: a certificate covers production of a specific engine family for a single model year; manufacturers may not build or sell engines beyond the certified production run without amending the certificate; importing uncertified engines — even for personal use — constitutes an unlawful act unless an exemption applies
• § 1068.115 — Emission warranty requirements: under CAA § 207(a), certifying manufacturers must warrant their emission-related parts to the first purchaser for the useful life of the engine — typically 5 years or 3,000 hours for small nonroad engines; specific components (catalysts, oxygen sensors, fuel systems) must be individually warranted; manufacturers cannot disclaim coverage for warranted components even if the owner uses aftermarket parts, unless the aftermarket part caused the failure
• § 1068.120 — Rebuilding engines: when a remanufacturer rebuilds an engine that was originally certified, it must restore the engine to at least the emission performance of the original certified configuration; rebuilding an uncertified engine to exceed the applicable standards does not produce a certified engine — it remains uncertified unless the rebuilder qualifies as a manufacturer and obtains a certificate
• § 1068.20 — EPA inspection authority: EPA may inspect manufacturers' testing facilities, manufacturing processes, storage facilities, and — critically — port facilities for imported engines at any reasonable time without advance notice; EPA inspectors may test any production or imported engine to verify it matches the certified family
• §§ 1068.201–1068.235 — Exemptions: Part 1068 codifies six exemption categories: (§ 1068.210) test engines used for research and development; (§ 1068.215) manufacturer-owned demonstration engines; (§ 1068.220) display engines for trade shows or museums (non-operational); (§ 1068.225) national security (DoD and cleared contractors); (§ 1068.230) export-only engines destined for countries without equivalent emission standards; (§ 1068.235) engines used exclusively for competition; each exemption requires documentation and, for large quantities, advance approval from EPA

Part 1068 is the reason "defeat device" is a legal term with consequences in U.S. law, not just a technical description. The Volkswagen Dieselgate enforcement (2015–2019) relied on 42 U.S.C. § 7522 and Part 1068's prohibition on defeat devices to impose over $14 billion in penalties on VW for approximately 580,000 vehicles whose engine control software detected EPA test conditions and temporarily improved emission performance during certification testing only. The same legal framework applies to nonroad diesel engines in construction equipment, generators, and marine vessels.

Fuel Economy Retrofit Device Evaluation Program (40 CFR Part 610)

40 CFR Part 610 — Fuel Economy Retrofit Devices (33 sections) is EPA's program for scientifically evaluating aftermarket devices that claim to improve vehicle fuel economy. The program was created under the Energy Policy and Conservation Act (EPCA) in response to a proliferation of aftermarket "fuel-saving" products — carburetor modifiers, air-intake devices, fuel line magnets, liquid additives, and electronic ignition boosters — that manufacturers marketed with unsubstantiated fuel economy claims during and after the 1970s energy crises. Key provisions:

• § 610.12 — Program initiative: an evaluation is triggered in three ways: (1) the Federal Trade Commission requests an evaluation after receiving consumer complaints or finding that the manufacturer's advertising claims are unfounded — the FTC's existing authority to police deceptive advertising was enhanced by the ability to cite EPA's scientific findings; (2) EPA initiates an evaluation on its own; or (3) a device manufacturer voluntarily submits its product for evaluation, gaining the benefit of a positive EPA finding for marketing purposes
• § 610.13 — Program structure: each evaluation has up to three phases — a preliminary analysis of existing test data; laboratory testing of the device's effect on fuel economy, emissions, and engine performance; and (for borderline results) extended in-use testing; manufacturers who submit devices voluntarily must agree to follow the procedures and bear program costs (§ 610.14)
• § 610.20–610.21 — Evaluation criteria: EPA classifies retrofit devices into functional categories (carburetion, air/fuel mixture, ignition, fuel line, and air intake) and tests each category's potential effect on the vehicle systems most relevant to fuel economy; the evaluation criteria focus on (a) fuel economy improvement as measured by EPA's standard dynamometer test (the same test used for new vehicle labels); (b) effect on exhaust emissions — devices may not cause the vehicle to exceed its certified emission standards; (c) device integrity under typical operating conditions; and (d) whether operator interaction is required for the claimed effect
• § 610.30–610.35 — Reporting and publication: EPA publishes its findings in the Federal Register; positive findings (demonstrating a statistically significant fuel economy improvement without increasing emissions) benefit the manufacturer; negative findings ("no demonstrated benefit") become public record — a potent regulatory tool because FTC can use a negative EPA finding as prima facie evidence that the manufacturer's advertising claims are false

The Part 610 program has been relatively dormant since the 1990s — the FTC's authority to pursue deceptive advertising directly has largely supplanted the formal evaluation request mechanism. However, the regulatory infrastructure remains active: any manufacturer who markets a device with fuel economy improvement claims on its label effectively operates under the shadow of a potential FTC-triggered Part 610 evaluation. The program documented many of the 1970s–1980s fuel-saving devices as ineffective or as increasing emissions — a body of testing that the EPA made available to the public and that FTC used in enforcement actions against marketers of ineffective products. The rise of electronic engine management systems has made most of the mechanical retrofit devices evaluated under Part 610 obsolete, but electronic "performance chips" claiming fuel economy improvements raise the same regulatory questions. No major rulemakings in 20+ years; the program structure dates from the 1979 original rule and has been stable.

Statutory Authority

This rule implements:

• 42 U.S.C. § 7521 — Emission standards for new motor vehicles: authorizes EPA to prescribe emission standards for hydrocarbons, carbon monoxide, NOx, and particulates for all classes of motor vehicles and engines
• 42 U.S.C. § 7541 — Compliance by manufacturers: establishes the emission warranty requirements (§ 7541(a)–(b)), the emission defect reporting requirement (§ 7541(c)), and EPA's authority to require manufacturers to recall and remedy vehicles found nonconforming in in-use testing (§ 7541(c)(1))
• 42 U.S.C. § 7522 — Prohibition of acts: prohibits manufacturers from selling uncertified new vehicles, defeat devices that circumvent emission controls, and tampering with emission control systems; provides the enforcement foundation for import restrictions

Recent Rulemakings

• Multi-Pollutant Emissions Standards for MYs 2027–2032 (89 FR 28152, April 2024): EPA finalized stricter tailpipe standards for light-duty and medium-duty vehicles, including more stringent NOx limits and tighter particulate matter standards. The rule tightened emission defect reporting thresholds in Part 85 to reflect new vehicle categories and updated the warranty requirements for zero-emission and plug-in hybrid vehicles, which have different emission components than internal combustion vehicles.
• Heavy-duty NOx standards update (88 FR 4472, January 2023): EPA finalized significantly tighter NOx standards for heavy-duty trucks (the "Clean Trucks" rule), phasing in from model year 2027. Companion changes to Part 85 updated recall and warranty provisions for heavy-duty engines.
• Volkswagen Dieselgate consent decrees (2016–2019): Following EPA's 2015 finding that Volkswagen installed defeat device software in approximately 580,000 diesel vehicles in the U.S., VW entered consent decrees requiring vehicle buybacks, emission modifications, and $14.7 billion in payments — the largest automotive environmental enforcement action in history. The case highlighted gaps in EPA's in-use testing program that have since been addressed through enhanced testing protocols.

Recent Developments

• Trump administration rollback of Biden EV mandate (2025): The EPA under the Trump administration announced its intent to reconsider or rescind the April 2024 Multi-Pollutant Standards rule (89 FR 28152), which established stringent tailpipe standards requiring a significant share of new vehicles sold in the 2027–2032 model years to be zero-emission. EPA initiated a formal rulemaking to weaken or replace the standards, citing manufacturer feasibility concerns and market readiness for EV adoption.
• California waiver litigation: California's authority to set its own vehicle emission standards — which other states can adopt under Clean Air Act § 177 — has been a recurring conflict. The Biden EPA reinstated California's Advanced Clean Cars II waiver in January 2023, but the Trump administration moved to rescind it in 2025. Fifteen states that had adopted California's standards faced regulatory uncertainty during the waiver dispute.
• Heavy-duty NOx implementation (model year 2027): EPA's 2023 Clean Trucks rule — setting the most stringent NOx standards ever for heavy-duty engines — takes effect beginning model year 2027. Truck manufacturers and engine makers are in production planning and certification testing phases. Some manufacturers have sought reconsideration of specific provisions, particularly those affecting high-idle and low-load engine operation.
• In-use surveillance and defeat device enforcement: Following the 2015 Volkswagen Dieselgate case, EPA has strengthened its in-use emissions surveillance program. EPA and DOJ have pursued enforcement actions against other manufacturers for alleged in-use emissions violations, including cases involving auxiliary emission control devices that reduce emission control system effectiveness under certain driving conditions.
• Light-duty certification backlog: EPA's vehicle and engine certification program has faced capacity constraints as the number of powertrain configurations (hybrid, plug-in hybrid, BEV, fuel cell) requiring certification has multiplied. Certificate of conformity delays have periodically constrained manufacturers' ability to finalize new model introductions.

Pending Action

The Trump EPA's proposed rescission or replacement of the April 2024 Multi-Pollutant Standards rule (89 FR 28152) is the dominant pending action. A formal proposed rule is expected in 2025–2026; watch the Federal Register for the EPA Administrator's signature on a NPRM addressing the 2027–2032 model year standards. Separately, the California Advanced Clean Cars II waiver rescission is being litigated in the D.C. Circuit — the outcome determines whether California and the 15 states that adopted its standards can maintain their own EV mandates or must revert to federal standards. Heavy-duty truck manufacturers should continue compliance planning for the 2027 model year Clean Trucks NOx standards, which are on a separate track from the light-duty reconsideration.