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Office of Transportation and Air Quality Frequent Questions

  1. Do those products that claim to improve fuel economy or lower emissions really work?
  2. How can I get a copy of the Certificate of Conformity for my car?
  3. Why is my gas mileage lower than the EPA rating?
  4. How can I get a copy of the Certificate of Conformity for a nonroad or heavy-duty highway engine?
  5. I just bought a used car and discovered the catalytic converter is missing. Is that legal?

1.   Do those products that claim to improve fuel economy or lower emissions really work? Some say that they are EPA-certified.

There are many fuel additives and/or aftermarket devices on the market that claim to save fuel and/or lower emissions. Some even claim they are approved or certified by EPA.

Under the Clean Air Act, a fuel additive (any substance or compound intended to be added to gasoline or diesel fuel) must be registered with EPA.  This means that the manufacturer of the product must provide EPA with certain information concerning the chemical composition of the additive, as well as submitting data to EPA that provides reasonable assurance that the use of the additive will not increase emissions of regulated air pollutants and will not pose a health or safety threat to the public. The registration requirements do not address the efficiency of the product or require any demonstration that the claims made for the product are valid (typically, "better fuel economy," and sometimes also "reduced emissions" or "engine life benefits").

Those marketing such products take advantage of this distinction, citing the fact that the product is "registered with the US EPA" and sometimes citing the applicable section of the Code of Federal Regulations (i.e., "under the provisions of 40 CFR Part 79") to foster the impression that EPA has somehow "approved of" or endorsed the product. For more information on the process by which fuel additives must be registered with EPA, and exactly what this does and does not imply, please see our Fuels and Fuel Additives Registration web site.

We have a program under which formal evaluation test programs are performed on aftermarket devices (generally, mechanical objects that are attached to or installed on a vehicle by the consumer) and on certain fuel additives. However, EPA does not certify, approve, or endorse any product tested in this program nor the results of any independent laboratory testing. EPA issues a technical report for those products and additives that we have tested and evaluated; these reports are available on our Web site at: www.epa.gov/otaq/consumer/reports.htm.

None of these products were found to produce statistically significant benefits in terms of fuel economy or exhaust emissions. When we explain all this to someone, the usual question we get back is "Why doesn't EPA stop them from doing this?"  EPA does not have the authority (or the resources) to attempt to stop such products from being marketed.  When the Federal Trade Commission (FTC), which can go after companies for false advertising, does manage to stop a company from marketing anything along these lines, the company and/or the product simply resurface under new names. 

Many people want to believe that there are in fact such "magic products" that will somehow greatly improve your vehicle's fuel economy (and hence reduce the costs of fuel), but when it comes to products and claims such as this, it’s wise for drivers to be skeptical. For more information, please read the following fact sheets on gas-saving products:

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2.   How can I get a copy of the Certificate of Conformity for my car?

a copy of the certifcate of conformity for a vehicle

To request or find a Certificate of Conformity and/or Certificate Summary Information sheet, you need to know the Test Group number (for light-duty cars and trucks – model year 2001 or later) or the Engine Family number (for pre-2001 light-duty cars and trucks). This information is listed on the “Vehicle Emission Information” label/sticker located under the vehicle’s hood. The number has 11 characters using both numbers and letters.

For Vehicles 2003 or Later

If your vehicle’s model year is 2003 or later, you can get the Certificate of Conformity and the Certificate Summary Information sheet by:

For Vehicles 2003 or Before

If you need a Certificate of Conformity or Certificate Summary Information for a vehicle with a model year before 2003, send the following information to EPA’s Imports Hotline (Imports@epa.gov). For telephone assistance, please call the Imports Team at (734)-214-4100. Or send fax requests to (734) 214-4676.

For Importing

All of the requirements for importing a vehicle into (or exporting from) the United States are described on the Imports site.

If you have any questions, please call the EPA Imports Hotline at 734-214-4100 or email them at Imports@epa.gov.

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3.   Why is my gas mileage lower than the EPA rating?

The fuel economy ratings are an estimate.

The purpose of the fuel economy ratings is to provide consumers with estimates to use in comparing the gas mileage of different vehicles. It is not meant as a guarantee of the gas mileage each driver will achieve. Since no test can simulate all the possible conditions that affect fuel economy, such as climate, driver behavior, road condition, and car care habits, your actual mileage will always vary some from the estimates.

Fuel economy estimates are determined by laboratory testing.

Fuel economy is measured under controlled conditions in a laboratory using a standardized test procedure specified by federal law. The fuel economy tests (which EPA updated in 2006 to more accurately account for actual driving conditions that can lower fuel economy, such as high speed, aggressive driving, use of air conditioning, and cold temperature operation), are based on a detailed driving cycle (each car is driven in exactly the same way, for exactly the same distance, with the same second-by-second vehicle speeds, to the maximum extent possible). The tests also are conducted under controlled conditions, using gasoline or diesel fuel that meet very detailed specifications. The goal of the laboratory testing is to control as many of the factors that affect fuel economy as possible, to the maximum degree that it is feasible to do so. Manufacturers test their own vehicles following EPA's test procedures—usually pre-production prototypes—and report the results to EPA. EPA reviews the results and confirms about 10-15 percent of them through our own tests at the National Vehicle and Fuel Emissions Laboratory. Additional information about fuel economy testing is available on the following sites:

Factors that affect Fuel Economy.

It is essential that EPA's fuel economy estimates continue to be derived from controlled, repeatable laboratory tests to enable a standardized or "level playing field," comparison between all vehicle models. Although EPA's fuel economy tests are designed to reflect typical driving conditions and driver behavior, several factors can significantly affect how many miles per gallon (mpg) your car gets: how and where you drive; vehicle condition and maintenance; fuel variations; vehicle variations; and engine break-in (this is described on Many Factors Affect MPG page. Because some vehicles are more sensitive to these factors than others, the impact of the changes will vary from vehicle to vehicle. The nature of current hybrid technology -- the addition of a battery as a second source of on-board power, sophisticated control systems, and sometimes a smaller engine -- makes a hybrid's fuel economy more sensitive to certain factors, such as colder weather and air conditioning use.

In May 2011, EPA and DOT’s National Highway Traffic Safety Administration (NHTSA) unveiled the redesigned fuel economy labels that provide the public with new information on vehicles’ fuel economy, energy use, fuel costs, and environmental impacts. For the first time, comparable fuel economy and environmental ratings will be available for all new vehicles, including advanced technology vehicles like electric cars. Consumers will be able to make comparisons—car by car —to ensure they have the best information to help save on fuel costs and reduce emissions.

Although EPA sets emission standards for pollutants that vehicle manufacturers have to meet, we do not set fuel economy standards for the vehicles currently on the market. Therefore, even if a vehicle does not achieve the EPA fuel economy rating, the manufacturers are not required to re-test or change the car for that specific model year. However, if a significant number of specific vehicle complaints are received, EPA has the option of performing confirmatory tests for the vehicle the following model year.

The U.S. Department of Transportation (DOT) does set fuel economy standards for cars and trucks through the Corporate Average Fuel Economy (CAFE) program. The standards are for the average fuel economy of the entire fleet of cars or trucks for a given model year as opposed to a specific vehicle or model. A penalty is assessed if a manufacturer's fleet does not meet the average standard and are enforced by DOT. For more information on CAFE visit DOT's CAFE web site at: www.nhtsa.gov/fuel-economy.

How to determine your vehicle’s fuel economy.

Given the above information, what is the best way to get realistic "city" and "highway" fuel economy numbers for your vehicle?  There is no "official" answer to that question, but we can offer you these suggestions.

To calculate the fuel economy in miles per gallon, take the number of miles driven and divide it by the total gallons purchased at refueling. For an even better estimate, take the average of two or three tanks in each case (city, highway). While there are minor variations over time, this allows you to monitor the vehicle's performance. A sudden drop in fuel economy not explained by the reasons noted below tells you that you may need to have maintenance done on your car.

To find out what you can do to improve the fuel economy of your car, please visit the following web site: www.fueleconomy.gov/feg/drive.shtml. Driving efficiently and keeping your car in shape will make a difference.

If your fuel economy is excessively low, your vehicle may need to be serviced or repaired. You may want to contact your dealer and ask them to check your vehicle and to determine that there are no outstanding defect reports or service bulletins which may affect fuel economy. The following are some of the diagnostic checks a mechanic will typically conduct for poor mpg:

If you are not satisfied with the outcome from the dealership, you can take your case to the Service Representative; the contact information should be listed in the owner’s manual. Be sure to document your observations thoroughly.

The Federal Citizen Information Center’s Consumer Action Web site provides information on warranties, recalls, and lemon laws at:  www.consumeraction.gov/caw_automobiles_warranties_lemon.shtml and lists contact information for car manufacturers at:  www.consumeraction.gov/carman.shtml. In addition, the Better Business Bureau’s Web site provides information on State lemon laws, which vary by state, at: www.bbb.org/us/auto-line/state-lemon-laws/. Exit EPA Disclaimer

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4.   How can I get a copy of the Certificate of Conformity for a nonroad or a heavy-duty highway engine?

To obtain the Certificate of Conformity data for a heavy-duty highway or nonroad engine, please send the following information to EPA’s Imports Hotline (Imports@epa.gov). For telephone assistance, please call the Imports Team at (734) 214-4100. Or send fax requests to (734) 214-4676.

For Importing/Exporting

If you are exporting a heavy-duty highway engine/vehicle or nonroad engine/equipment to another country, the government sometimes requests the test data. You will need to know the Engine Family number (found on the emission label) to obtain this information. You can access test data for heavy-duty highway engines or nonroad engines for 1998 to the present on EPA’s Web site as follows:

All of the requirements for importing a vehicle into (or exporting from) the United States are described on the Imports site.

If you have any questions, please call the EPA Imports Hotline at (734) 214-4100 or email them at Imports@epa.gov.

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5.   I just bought a used car and discovered the catalytic converter is missing. Is that legal?

The act of removing a catalytic converter without replacing it with an approved replacement (known as "tampering") is illegal under federal law and is of great concern to EPA because of the high pollution levels that are emitted by vehicles without properly functioning emission controls. The original antitampering law was part of the Clean Air Act of 1970; it applied only to manufacturers and car dealers. The antitampering law was expanded by the 1977 Clean Air Act Amendments to apply to all automobile repair facilities, commercial mechanics, and fleet operators. And the 1990 Clean Air Act Amendments (CAAA) broadened the tampering provision even further; it now applies to everyone, including car owners. Here is the text from the 1990 CAAA:

"Section 288 – Enforcement
(b) TAMPERING WITH VEHICLE EMISSION CONTROLS – (1) Section 203(a)(3) (42 U.S.C. 7522(a)(3)) is amended to read as follows:

'(3)(A) for any person to remove or render inoperative any device or element of design installed on or in a motor vehicle or motor vehicle engine in compliance with regulations under this title prior to its sale and delivery to the ultimate purchaser, or for any person knowingly to remove or render inoperative any such device or element of design after such sale and delivery to the ultimate purchaser; or

'(B) for any person to manufacture or sell, or offer to sell, or install, any part or component intended for use with, or as part of, any motor vehicle or motor vehicle engine, where a principal effect of the part or component is to bypass, defeat, or render inoperative any device or element of design installed on or in a motor vehicle or motor vehicle engine in compliance with regulations under this title, and where the person knows or should know that such part or component is being offered for sale or installed for such use or put to such use; or '

(2) At the end of section 203(a) (42 U.S.C. 7522(a)) insert the following:

'No action with respect to any device or element of design referred to in paragraph (3) shall be treated as a prohibited act under that paragraph if (i) the action is for the purpose of repair or replacement of the device or element, or is a necessary and temporary procedure to repair or replace any other item and the device or element is replaced upon completion of the procedure, and (ii) such action thereafter results in the proper functioning of the device or element referred to in paragraph (3). No action with respect to any device or element of design referred to in paragraph (3) shall be treated as a prohibited act under that paragraph if the action is for the purpose of a conversion of a motor vehicle for use of a clean alternative fuel (as defined in this title) and if such vehicle complies with the applicable standard under section 202 when operating on such fuel, and if in the case of a clean alternative fuel vehicle (as defined by rule by the Administrator), the device or element is replaced upon completion of the conversion procedure and such action results in proper functioning of the device or element when the motor vehicle operates on conventional fuel.'."

The resale of a vehicle which has already had the catalytic converter removed is not specifically addressed by federal law. Therefore, the person who removed the converter violated federal law, but not necessarily the person who sold the vehicle. However, the sale of vehicles that have had the emission control system removed, disabled, or tampered with may be further governed by state or local laws.

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