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Exhaust and Emissions Testing

Learn about the importance of exhaust and emissions testing for your car.

Exhaust and emissions testing ensures that cars don't pollute the air. [©Jupiter Images. 2009]
©Jupiter Images. 2009
Exhaust and emissions testing ensures that cars don't pollute the air.

States require exhaust and emissions testing in well-traveled metropolitan areas to identify motor vehicles that are responsible for releasing air pollutants above federal health standards. States typically require motorists to undergo vehicle exhaust and emissions testing every other year in order to register their vehicles. If a vehicle fails the test, it must be repaired and retested before it can be registered.

Importance of Exhaust and Emissions Testing

Motor vehicles pollute through the emission of carbon monoxide and volatile organic compounds. Because of this, the federal government passed the Clean Air Act, which outlines standards that all areas must meet. State-administered vehicle exhaust and emission inspection programs are required in areas that violate the standards, which are typically urban areas, according to the Wisconsin Department of Transportation.

Exhaust and emissions testing ensures that a car is not polluting the air excessively. The California Bureau of Automotive Repair reports that its "Smog Check Program" removes 400 tons of pollutants from the air each day. According to Idaho's Air Quality Board, 10 percent of vehicles contribute to half of all air pollution. Vehicle exhaust and emissions can cause ozone buildup, commonly known as smog. Newer vehicles typically have more sophisticated emissions control equipment, but they still need to be tested to ensure that this equipment is working properly. Older vehicles do not have such equipment and may be emitting pollutants that don't meet health standards.

Exhaust and Emissions Testing Requirements

Vehicle exhaust and emissions testing is mandatory, but generally only in highly traveled urban areas. For example, in Arizona, testing is required only in the Phoenix and Tucson metropolitan areas, according to the Arizona Department of Environmental Quality.

When exhaust and emissions testing is required, it is usually every other year, although older vehicles may require annual tests, according to the Utah Department of Motor Vehicles. In California, cars that are less than six years old must undergo testing every other year, and some vehicles may be exempt from testing. New vehicles may require less regular inspections. For example, in New Jersey, new vehicles do not need exhaust and emissions testing for four years, according to the State of New Jersey Motor Vehicle Department. Gasoline, dual fuel and diesel-powered vehicles are all subject to emissions tests, according to the Alaska Division of Motor Vehicles. Hybrid vehicles must also be tested. Individuals should check their state's department of transportation, which will generally provide detailed information about requirements on its Web site along with garages that have the equipment to perform the tests.

How It Works

If their vehicle needs a test, individuals are notified when they receive their registration renewal notice. Testing costs about $15, depending on the state, and car owners must take their vehicles to a garage with emission testing equipment. Typically, two different types of tests are performed at garages:

  • On-board diagnostic (OBD) tests: These tests are usually performed on newer-model vehicles, light-duty trucks and sport utility vehicles. An OBD test consists of connecting a vehicle's onboard computer to a scan tool to determine if the equipment is in proper working order.
  • A single-speed idle exhaust test and gas cap pressure test:This test is performed on heavy-duty trucks. The carbon monoxide and hydrocarbon pollutants from the vehicle exhaust are measured as the vehicle idles. The gas cap test checks the cap's seal to ensure that fumes aren't released into the air. For a diesel vehicle, exhaust may be tested with a snap acceleration test that simulates on-the-road acceleration.

If a vehicle fails the test, it means it's not running properly and is polluting the air. Individuals whose vehicles fail usually have 30 days to have the emission problem fixed. After this, they must have their vehicles retested. In most states, the recheck is free if it's done within 30 days, but individuals who wait longer than this must pay again.

Preparing for the Test

Some states, such as Illinois, publish report cards, essentially grading repair shops on their ability to correct emissions problems. Others offer lists of certified repair shops. However, Georgia's Clean Air Force recommends that motorists inspect their own cars before undergoing emissions tests. This will reduce the chance of failure. Specifically, vehicle owners should do the following:

  • Get routine tune-ups that look for failed components that most frequently cause botched exhaust and emissions tests. These include the oxygen sensor, EGR valve, dirty air filters, misfiring spark plugs, vacuum system leaks and ill-fitting fuel caps.
  • Change oil regularly.
  • Make sure the fuel cap is secure and clean.
  • Check belts and hoses.
  • Keep tires inflated to proper levels.

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