What is an emissions test?

A car emissions test checks the emissions of your vehicle to make sure that the greenhouse gases and pollutants released by your car fall within your state's legal limits. Car emissions testing is often conducted by connecting your car to a testing system through your car's onboard diagnostics port (OBD2 port). For older vehicles that don't have this option, testing sites will put your car on a dynamometer (essentially a treadmill for your car) and attach a sensor to your tailpipe.

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What do they check for during an emissions test?

Emissions tests may check the levels of any or all the following in your exhaust: benzene (C6H6), carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC), oxygen (O2), nitrogen oxides (NOx), sulfur dioxide (SO2), and particulate matter. Some of these emissions are checked due to their impact on human health, while others are examined due to their impact on the environment.

Which states require vehicle emissions testing?

There are 34 states that require emissions testing for cars, and exact rules vary widely by state. Some states only require testing in certain areas of the state, including certain counties and metropolitan areas. Check with your local DMV or BMV for the exact rules in your area.

California has implemented the strictest laws around emissions testing, and many other states have used California as a model for their emissions testing over the years.

How do I find out if my car needs an emissions test?

When an emissions test is required, it's usually tied to your vehicle registration process. When you need to renew your vehicle registration, part of that renewal notification will usually include a reminder that you're due for an emissions test. How often your vehicle needs an emissions test will vary by state, county, or city. Check with your state's DMV or BMV to see how often you need to test your vehicle or if your car is exempt from emissions testing.

How long is an emissions test good for?

The exact timeframe varies by state, but an emissions test will typically last one to two years. Contact your department or bureau of motor vehicles (DMV or BMV) for more information.

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