US: Compliance and Enforcement

US: Compliance and Enforcement


The page outlines the mechanisms that are used in the United States to ensure compliance with clean air, vehicle emissions, and vehicle fuel economy standards.


The US vehicle compliance program is by far the most comprehensive and far-reaching compliance program in the world. Before the Clean Air Act (CAA) was passed in 1970, the US had a vehicle compliance program that only covered new vehicle certification.1 The 1970 CAA changed that, adding authority for the EPA to assure that vehicles coming off the assembly lines meet standards. It also authorized the EPA to hold manufacturers responsible for vehicles meeting standards throughout their useful lives, provided that customers properly maintain their vehicles. Lastly, the CAA also required manufacturers to warrant individual emissions control components on vehicles to protect consumers. Over the years, the EPA compliance program has grown and evolved from one that focuses mainly on ensuring that prototype and new production vehicles comply with standards to one that places strong emphasis on in-use testing to ensure emissions standards are met over the useful life of a vehicle. The development of on-board diagnostics (OBD) systems have aided in this process.

The EPA was able to shift resources to in-use vehicle testing programs over time because of initially strong and vigorous certification and Selective Enforcement Audit (SEA) programs. These initial programs deterred fraudulent reporting of certification results and compelled manufacturers to extensively test new vehicles, at their own cost, to ensure production conformity. This allowed EPA to shift its resources to ensuring engines and emission control devices are durable and that emissions are effectively controlled over the useful life of vehicles. The development of portable emissions measurement systems (PEMS) and OBD systems for in-use emissions measurements makes in-use emission testing feasible.2

EPA Light-Duty Vehicles (LDVs) Compliance Program

The new vehicle compliance and enforcement program for LDVs (including two and three-wheelers) consists of:

  1. Pre-production certification,
  2. Confirmatory testing,
  3. Selective enforcement audit (SEA),
  4. In-use surveillance performed by EPA,
  5. In-use verification performed (IUVP) by the manufacturer,
  6. Recall in case of noncompliance, and
  7. Warranties and defect reporting.

Pre-production certification testing

Under the CAA Section 206, all engines and vehicles sold in the US are required to be covered by a certificate of conformity before they can enter the market. The certification demonstrates that the engine or vehicle conforms to all applicable emissions and fuel economy requirements. A deterioration factor is applied to the test results before a vehicle passes or fails.3

Pre-production certification testing is conducted by manufacturers to support their applications for certificates of conformity, and is usually performed before a certificate is issued.4 A manufacturer can establish its own testing facility to conduct the test or contract the services of independent laboratories. Test results, adjusted with deterioration factors, must be recorded in the certification applications to demonstrate compliance. Manufacturers must perform certification testing for all “test groups” that they choose to certify.

A test group or engine family is a basic classification unit used for demonstrating compliance with vehicle emissions requirements. It is a group of vehicles or engines having similar design and emission characteristics. For light- and heavy-duty vehicles, these characteristics include engine displacement, cylinder number, arrangement of cylinders and combustion chambers (in-line vs. v-shaped), and subject to the same type of emission standards. The manufacturer is required to select a vehicle configuration within every test group that is expected to generate the highest level of emission and emission deterioration as the test vehicle (the worst-case configuration). The selected configuration is called the emission data vehicle.5

Manufacturers submit certification applications through EPA’s computer system, called VERIFY, which automatically validates all applications. Manual auditing is performed for some applications. The EPA issued over 3,600 conformity certificates to vehicle and engine manufacturers, each year, in 2007 and 2008.6

Confirmatory testing

The EPA performs both targeted and random confirmatory tests at its Ann Arbor lab, or at a contractor’s or manufacturer labs. Engines are selected for targeted confirmatory tests based on various criteria including: 1) compliance history with a manufacturer; 2) compliance margin of the engine; 3) use of new technologies; 4) other information the agency might have regarding an engine family. The EPA does not issue a certificate of confirmation for any heavy-duty or non-road engine that fails confirmatory tests.

The EPA started performing confirmity testing for non-road engines in 2006, and has expanded the test to categories such as lawn and garden equipment.6

Among the 676 heavy-duty land-based non-road engines (typically called agricultural and construction engine) certified in MY2007, EPA tested eleven. EPA’s primary focus in 2007 was on non-road engines. It did not test any on-road heavy-duty engines that year.

In 2008, EPA issued seven confirmatory test orders for agricultural and construction engine families, and 10 test orders for lawn and garden engine families. All agricultural and construction families passed the confirmatory tests. For the lawn and garden engine families, under half passed, over 20% failed, and the rest withdrew their applications for certification. Engine families not tested were not issued a certificate of conformity, and were not allowed to be sold or imported in the US. Again, the EPA did not conduct conformity tests for on-road heavy-duty engines in 2008.

The EPA allows manufacturers to participate in an Averaging, Banking, and Trading (ABT) program. Under this program, manufacturers with vehicles well below set limits are allowed to accrue positive emission credits and use those for other models that are having difficulty meeting limits. Manufacturers are also allowed to sell or swap credits to each other.8 The ABT program allows for flexibility in compliance while still assuring fleetwide emission standards are met.

Confirmatory tests are targeted and random tests performed by EPA to validate the emission and fuel economy testing results reported in certification testing. In recent years, EPA selected about 15% of all test groups for confirmatory testing; two-third of the selected test groups (10% of all test groups) are randomly selected and the remaining one-third (5% of all test groups) are targeted test group.9 All LDV confirmatory tests are currently conducted at EPA’s Ann Arbor laboratory.10

The majority of vehicles targeted for confirmatory test are those models that use new technology or new design. Others are targeted due to potential emission concerns, including models with certified emission levels very close to the standards (small emission margin).

Manufacturers are invited to observe how the tests are performed. Every test vehicle has two attempts to pass. If the vehicle fails the first test, it is tested a second time. The manufacturer can also choose to inspect the test vehicle after the first failure to determine what went wrong. If a vehicle fails two valid tests, no certificate will be issued. The manufacturer can choose to not pursue certification, or make changes (recalibration) and then submit a new application.

Selective enforcement audit (SEA)

The SEA program came about in the mid-1970s when EPA found that manufacturers were occasionally producing classes of new vehicles that did not comply with standards, even though the certified prototypes met the standards. The SEA is aimed at identifying cases where prototype vehicles supplied by manufacturers are not representative of production.

Under the SEA program, EPA can require manufacturers to test vehicles pulled straight off the assembly line, at the manufacturer’s expense, without prior notice. The SEA gives the EPA an opportunity to assess, early on, whether certified vehicles are actually being built adhering to the specifications of the prototype. It also serves as a check to see if manufacturers are allowing sufficient compliance margins such that engine and emissions control equipment functions effectively to comply with standards after deterioration factors are applied.

The SEA was designed based on the premise that testing a fixed percentage of all assembly line vehicles was not necessary; rather, a program that focused on potentially suspect classes could achieve the same goal at a lower cost to the industry. To pick the target test groups for auditing, EPA used information from many different sources, including compliance history with a manufacturer, compliance margin, certification data, I/M data, technology reviews, and defect reports.

SEA audits can be performed at the manufacturer facility, following EPA requirements, or at any testing lab EPA chooses. If a model fails SEA testing, EPA has the power to revoke or suspend certification, which will restrict sales of the model until the manufacturer can demonstrate conformity with the standards.

Because penalties for failing the SEA tests were disruptive to manufacturers, many manufacturers now routinely test their own vehicles. Soon after the program started, manufacturers began testing 100 times as many vehicles as the number of vehicles audited by the EPA. By the mid-1980s, failed LDV audits became rare as individual vehicles failures under the SEA program became infrequent. This led the EPA to shift LDV SEA staff and resources to HDV SEA efforts and in-use vehicle testing programs.11

EPA has not conducted any SEA for LDVs in recent years, but the agency reserves the right to conduct SEA tests if problems such as reporting fraud or improper testing are suspected.

SEA for non-road engine testing

EPA is planning to expand the use of SEA for non-road engine testing. The SEA is a more useful tool for non-road engines than for LDVs because compliance with non-road new engine standards is verified by engine testing, and it’s much easier to assess compliance of an engine before it is installed into equipment.

If a non-road engine in a test group fails an SEA, the manufacturer needs to identify and correct the problems until the engine can pass. If the entire engine family fails, EPA can pursue follow-up actions, such as forcing a manufacturer to stop production.

In-use surveillance and recall testing program

The LDV SEA program has largely been replaced with an in-use surveillance and recall testing program. This program either targets vehicle classes that are suspected of having emission-related problems, or targets populations that are chosen to be sampled for other reasons. Vehicle classes could be selected based on: 1) manufacturer defect reports; 2) information from state I/M programs; 3) manufacturer service bulletins; 4) certification test results (EPA more likely tests vehicle models that have had problems in certification), 5) newer technology or engine, 6) sales volume, 7) In-use Verification Program (IUVP) failures, 8) random, or 9) any other reason EPA deems appropriate.

All selected vehicles are tested at the Ann Arbor laboratory (unless designated by EPA), following the same test procedures and fuels (standard fuels) used in certification. Manufacturers are contacted if their vehicles are picked for in-use testing, and they are invited to watch the tests being performed and maintenance being performed on the vehicles, so they have confidence of the quality of the tests.

To conduct surveillance, EPA typically recruits three to five vehicles that are two or three years old from the Southeastern Michigan area (in proximity to the Ann Arbor lab). EPA’s contractor contacts vehicle owners from each of the test groups selected by EPA for testing. The owners are given small monetary awards (about US$20 per day) and a loaner car (or US$50 per day in lieu of a loaner car). EPA ensures that the cars have been properly maintained and used and, if needed, performs required maintenance before testing. The maintenance performed depends on program requirements. Participants are given a list of any parts that are replaced.

If a number of failures are identified in the surveillance testing, EPA will discuss these with the manufacturer to determine acceptable resolutions, such as a voluntary recall, field repair, or an extended warranty. EPA rarely uses forced recall but reserves the right to use it as a last resort.

In 2007, a total of 142 vehicles were tested, representing 47 test groups. Nine vehicles (representing five test groups) failed the in-use tests, but only one test group showed an extent of failure that warranted further investigation.6

Testing enters the confirmatory phase if the surveillance results indicate that a substantial number of vehicles in a class may exceed emission standards within the useful life and if the manufacturer declines to voluntarily remedy the problem at that time. This step could lead to an EPA-ordered recall if testing were to confirm the likelihood of a substantial number of vehicles failing within the class. The manufacturer can voluntarily recall the vehicles at any time to avoid this process. EPA will work with manufacturers to agree on appropriate remedies to avoid an ordered recall. However, EPA has the authority under Section 207(c) of the Clean Air Act to order a recall if voluntary measures are not agreed upon.

Vehicle recruitment and testing in the confirmatory testing process are much more rigorous than in surveillance testing, because vehicles must be shown to fail when properly maintained and used. Usually, ten randomly selected vehicles from within the class in question that have been properly maintained and used are tested. EPA reviews the results of the confirmatory testing and makes a determination whether the failure rate indicates if a substantial number are failing. Generally, if more than two of the vehicles in the sample fail, there is risk of further action. The manufacturer has the opportunity to take voluntary action prior to EPA issuing an official finding.13

In the New Compliance Assurance Program (CAP2000) adopted by EPA in 2000, the in-use conformity phase becomes the IUVP program, as discussed below.

In-use verification program (IUVP) and in-use confirmatory program (IUCP)

The IUVP is designed to test emissions of both low-mileage (10,000 miles or 16,000km) and high-mileage (50,000 miles or 80,000km) in-use vehicles. Manufacturers are responsible for testing one to five vehicles per test group. About 2,000 industry-wide tests were performed in 2007. If 50% of vehicles in a test group fail, and the average emission levels are greater than 1.3 times the standard limits, the manufacturer must automatically conduct an IUCP test. In the IUCP, test vehicles are selected and tested in a more rigorous manner (in the same manner as confirmatory testing described above). Failure of IUCP tests can lead to recall.

Manufacturers are required to report all IUVP data to EPA. This large database allows the EPA to concentrate on future vehicle design issues, particularly on the deterioration of emissions control devices under real life driving conditions. IUVP data is also used to assess and update the deterioration factors and procedures used to determine them.

In addition to manufacturer conducted IUVP and IUCP tests, the EPA itself conducts in-use surveillance tests either at its Ann Arbor, Michigan facility or at authorized testing centers. Vehicles can be selected at random, or they can be targeted based on data suggesting particular vehicles require additional EPA testing.


The US CAA authorizes the EPA to require a manufacturer to recall vehicles or engines, at their own expense, if it is determined that a substantial number of vehicles or engines from that group do not meet the standards.

The EPA can require a recall when a test group fails IUCP testing. EPA could also require a recall based on the IUVP data. Manufacturers typically prefer to launch voluntary recalls when they are presented with data, rather than wait until they are obligated to. If a manufacturer refuses to a voluntary recall, EPA can follow established regulatory procedures to order a recall.

Some recall campaigns involve defects that occur in a small number of vehicles within a class, where the malfunction is so evident to the vehicle owner that they seek repair. These are usually termed “self-campaigning.” If these defects result in emissions failures, and occur outside of the warranty period for the emission-related component, manufacturers can conduct a warranty extension campaign where owners are notified of the potential failure and that the repair will be covered for a certain time and mileage. The EPA deems these recalls to be voluntary service campaigns, and encourages manufacturers to conduct them when a full-fledged recall is not appropriate.

Warranty and defect reporting

The CAA requires manufacturers to warranty certain emission control components on their vehicles. Such warranties protect vehicle owners from the cost of repairs for emission-related failures that cause the vehicle or engine to exceed emission standards.

There are two types of warranties: Performance Warranty and Design and Defect Warranty. The Performance Warranty covers any repair or adjustment that is necessary to make a vehicle pass an approved, locally-required emissions test (like an I/M) during the first 2 years/24,000 miles of vehicle use. The vehicle must have been properly maintained according to the manufacturer’s specifications and have not been misused. Specified major emission control components, like catalytic converters, electronic control units, and onboard diagnostic devices, are covered for the first 8 years or 80,000 miles, however. The Design and Defect Warranty covers repair of emissions related parts that become defective because of a defect in materials or workmanship during the warranty period. The warranty period for all emission control and emissions related parts is 2 years or 24,000 miles of vehicle use. For specified major emission control components, it is 8 years or 80,000 miles of vehicle use.14

EPA requires manufacturers to monitor known defects in emission control systems of properly maintained and used engines. They must submit defect reports to EPA whenever 25 or more vehicles within the same model year are found to have particular emission-related defects. The defect reports must estimate the proportion of vehicles that contain a defective part and estimate the impact of the defect on emissions. A recall can be initiated if as little as 1% of an engine family has the same defective part assuming the defect has a significant impact on emissions.

EPA Heavy-Duty Vehicle (HDV) and Non-Road Engine Compliance Program

Key elements of the heavy-duty and non-road engine enforcement and compliance program include: 1) Pre-production certification, 2) Confirmatory testing, 3) Selective enforcement audit, 4) Manufacturer production line testing, 5) In-use testing performed by EPA and manufacturers, 6) Warranties and defect reporting, 7) Recall if necessary.

Pre-production certification testing

Similar to the LDV program, all heavy-duty (HD) engine manufacturers are required to test new or modified HD engines to demonstrate compliance. They must submit test results as part of the certification application to EPA prior to production.

HD engine certification is based primarily on engine testing as opposed to chassis dynamometer testing of the entire vehicle. Using rationale similar to that applied to LDVs, certification tests are performed on an engine that represents the highest emissions level of an engine family (comparable to a test group). Deterioration factors are applied to the testing results before comparing test data with applicable standards and determining compliance.

Manufacturer production line testing

To assure that emissions from manufactured are in line with prototypes, manufacturers are required to routinely test engines as they leave the assembly line. Production line testing is now used primarily done for non-road engines, because once an engine is installed into non-road equipment it is difficult and costly to remove it for testing. Another challenge is that in-use testing for non-road equipment using portable emission measurement systems (PEMS) is not as well developed as for HDVs.

In-use testing by EPA and manufacturers

Traditional laboratory testing for HD and non-road engines over a specific test cycle requires the engine be removed from the vehicle or equipment. This makes it prohibitively expensive and cumbersome to conduct in-use testing for HD and non-road engines. In addition, HD and non-road engines operate in a wide range of conditions (load, speed) that cannot be fully represented in limited test cycles. Laboratory testing following a specific test cycle cannot ensure that emissions from these vehicles and pieces of equipment are within the range of the applicable standards during normal operation. There has been a long-standing need for more accurate measurement of HD and non-road engine emissions under real life operation (in-use emissions). The development of the portable emissions measurement systems (PEMS) and the incorporation of these systems make it possible for EPA to monitor and verify compliance of the HD and non-road engines during normal operation.

Collaborating with the California Air Resources Board (CARB) and diesel engine manufacturers, the EPA launched the in-use testing program for HD trucks and buses in 2005. Under this program, the EPA, CARB and manufacturers measure in-use emissions of HD engines using PEMS, and compliance is determined against not-to-exceed (NTE) standards.15

The EPA in-use testing is conducted at the Ann Arbor lab and at the Department of Defense testing lab at Aberdeen in Maryland. In 2007, EPA tested 54 truck models and 72 non-road equipment using PEMS. For HDVs, the majority of in-use tests are conducted by manufacturers as part of the requirements of the HD in-use testing rule.16 Manufacturers are required to demonstrate compliance with the NTE limits, which is generally 1.25 or 1.5 times the applicable federal test procedure (FTP) standards. The EPA will designate no more than 25% of a given manufacturer’s engine families (with production volume greater than 1,500 engines) for in-use testing every year. Because of the wider variations of in-use testing measurements, EPA initiated a comprehensive research, development, and demonstration program designed to identify new accuracy measurement margins for PEMS.

EPA established a mandatory pilot in-use testing program for gaseous pollutants in 2005 and 2006, and for PM pollutants in 2007 and 2008. The program became fully enforceable for gaseous pollutants starting in 2007, and for PM in 2009.

Exceedences of the NTE limit during in-use testing do not necessarily represent a violation or noncompliance because of flexibility given to manufacturers to comply with the standards. The EPA makes decisions on a case-by-case basis, and no action has been taken to date.

Show 16 footnotes

  1. Clean Air Act (legislative text) U.S. Congress, 1970.
  2. Freed C, Fung F, 2010.
  3. The deterioration factor is an essential part of testing for pre-production certification, as well as for selective enforcement audits and conformity of production discussed in the later part of this chapter. EPA has adopted a durability demonstration regulation on how to determine deterioration factors. Each manufacturer is required to design a durability process that predicts the in-use deterioration of the vehicles it produces. Most manufacturers determine deterioration factors using accelerated bench aging procedures for emission control components. The manufacturer-funded in-use testing program (In-use Verification Testing Program) discussed later in this chapter provides valuable data to validate manufacturers’ procedures for determining deterioration factors. If in-use testing shows larger deterioration factors, the manufacturer must revise their procedures for determining deterioration factors.
  4. Certification testing in the US comprises the following test procedures: federal test procedure (FTP), highway fuel economy test, US06 (high speed/acceleration cycle), SC03 (air conditioning test cycle), cold CO (FTP conducted at 20 degrees F), evaporative emissions, Onboard Refueling Vapor Recovery (ORVR), and running loss emissions test. For information on test cycles, see the US Test Cycle page.
  5. Title 40 Part 86 – Control of Emissions from new and In-use Highway Vehicles and Engines, Part 1 (Volume 15) Part II (Volume 16), N.A.a.R. Administration, Editor 2011.
  6. 2008 Progress Report – Vehicle and Engine Compliance Activities, 2010, EPA.
  7. 2008 Progress Report – Vehicle and Engine Compliance Activities, 2010, EPA.
  8. Control of Air Pollution from New Vehicle Emissions; Heavy-Duty Engine Standards and Diesel Fuel Sulfur Control Requirements, EPA, 2000.
  9. 2007 Progress Report – Vehicle and Engine Compliance Activities, 2007, EPA
  10. The EPA can require additional confirmatory tests to be conducted by manufacturers future if need be.
  11. Freed C, Fung F, Editor 2010.
  12. 2008 Progress Report – Vehicle and Engine Compliance Activities, 2010, EPA.
  13. Harrison D. In-use Vehicle Compliance Management in the United States. in Vehicle Pollution Control International Workshop. 2006. Beijing, China.
  14. Emissions Warranties for 1995 and Newer Cars & Trucks, EPA, 1996.
  15. The NTE requirements establish an area or zone under the torque curve of an engine where emissions must not exceed a specified value for any of the regulated pollutants.
  16. Regulatory Announcement: Amendments to the Manufacturer-run, Heavy-Duty Diesel In-Use Engine and Vehicle Testing Program, EPA, Editor 2008.

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