Smog check, smog test and emission check all refer to the same thing: a test of a vehicle and its engine emissions performed at a licensed smog testing facility. Smog checks are regulated by the U.S. Environmental Protection Agency (EPA), whose goal is to protect public health and the environment from the dangerous effects of air pollution. In 1990, the Clean Air Act gave the EPA its authority to oversee states with respect to emissions.
California is the only state that is allowed to adopt its own emissions standards and these are the toughest standards in the nation. Other states can either implement the Federal or the California emissions standards. Thirty-one states require emissions testing or smog checks, though regulations vary. For example, in Missouri, emissions tests are required only in the St. Louis metropolitan area, and in Illinois and Wisconsin, it’s required only in certain counties.
Smog check history is a little convoluted, since it’s regulated state by state, and some states have even phased out or discontinued their testing procedures in recent years. However, in March of 2024, the EPA passed new regulations for federal emissions standards, which will phase in starting in 2027.
What is a smog check?
During a smog check, a licensed technician will attach measuring equipment to your vehicle. The smog check test may consist of emissions inspection, visual inspection, and functional inspection, all of which ensure your emissions equipment is in place, functioning, and doing its job of weeding out pollutants from your car’s exhaust.
How much is a smog check?
How much does it cost to have a smog check? That varies based on location. Generally, you can expect to pay $20 to $50 for the test. In some states, such as Illinois, the test is free.
Where to find deals on a smog check
A smog check price varies, but you can sometimes pay less. Why pay full price for a smog check – especially if this is an annual requirement in your state, county or metro area? The easiest way to find smog check facilities offering deals is to do an online search for “smog coupons” or “smog check coupons” in your zip code. You’re most likely to be able to find discounts in states such as Arizona and Nevada, where testing facilities are privately owned. While Nevada’s DMV caps the maximum test fee, these facilities can offer discounts but must be transparent in pricing with official signage and documentation.
Many smog check centers place ads in local printed media, offering smog check test discounts up to 30 percent. Keep in mind that coupons or discounts may have terms and conditions attached, so it pays to read the fine print.
Bottom line: Depending on where you live, there may be many licensed smog check stations and facilities to choose from. Since the prices may be considerably different for the same testing, shop around for the best deal to save money on this recurring (for some) vehicle expense.
What happens during a smog check?
Wondering what will happen when you arrive, or how long does a smog check take? It’s typically pretty simple. The technician is responsible for visually inspecting your vehicle and using special equipment to test your vehicle’s emissions for certain pollutants. Emissions measured include carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC) and oxygen (O2). In some of the nation’s most polluted urban areas, the emissions test also measures levels of oxides of nitrogen (NOx).
What is the testing process?
If you received a notification in the mail that your vehicle is due for a smog test or must be checked before your registration renewal, bring the documentation with you to the test center. After a quick visual inspection, your vehicle will be hooked up to the test equipment. During the smog check, the measurements taken are recorded and immediately available to your state’s agency responsible for monitoring smog and vehicle emissions. For example, in Georgia, data goes to the Georgia Clean Air Force (GCAF). In California, it is transmitted to the Bureau of Automotive Repair (BAR).
Cities, states and counties that require smog and emissions tests for DMV car registration determine which testing method or combination of methods to use. Current testing methods include:
Two-speed idle (TSI) – this test analyzes exhaust emissions from the tailpipe as the engine idles first at high, and then at low speed, and is usually for older cars registered before 1995.
Acceleration simulation mode (ASM) – Again, most often reserved for older vehicles, the ASM test measures emissions under simulated driving conditions using a dynamometer.
On-board diagnostics (OBDI) – During this test, information is downloaded from the vehicle’s on-board diagnostics computer.
Following completion of the smog check, whether pass or fail, the technician will give you a copy of the test results, called the Vehicle Inspection Report (VIR), along with a receipt for payment of the smog check.
If your vehicle fails the smog check, you can choose to have it repaired at a licensed test and repair station and then have it retested to pass the smog check. In most states, vehicles that have not passed inspection are not allowed on public roads and owners will be ticketed if they are caught operating those vehicles beyond a grace period to complete necessary repairs.
What are exemptions?
Most states require vehicle emissions testing every two years, but not every vehicle requires a smog check. In California, for example, whether or not a smog check is required depends on the type of vehicle, the model year, and the area in which the vehicle is registered. Vehicles that are six or less model years old in California are not required to have the biennial smog check.
In New York, like California, registration renewal notices mailed to owners contain a warning message if there’s no record of a valid emissions and regular safety inspection on file (inspections are required annually). Vehicles exempt from the emissions inspection program are those that are less than two years old, 26 model years old or older, registered with historic plates, or are electric-powered only.
The best way to determine if your state, city or county requires a smog check is to go to your state DMV website.
Where to get a smog check
Only certified smog check stations can perform smog and vehicle emissions testing, though the process varies by state. For example, some states authorize independent mechanics and shops to perform emissions testing, while in other states, the testing facilities are state owned and operated. Check your state’s Department of Motor Vehicles (DMV), Department of Public Safety, or other agency for links to approved smog check facilities. Here are a few examples:
In Tennessee, testing information and station schedules are available through the Tennessee Department of Environment and Conservation (TDEC).
The Nevada DMV has an online listing of emission stations.
Test station information is available in Connecticut from the Connecticut Emissions Program.
In Texas, the Texas Department of Public Safety lists Recognized Emissions Repair Facilities for motorists whose vehicles fail the emissions test.
Massachusetts.gov provides an online locator for Massachusetts vehicle inspection stations and registered emissions repair shops.
The Georgia Clean Air Force website lists links for information on other state’s emission testing.
Tips on how to pass a smog check
It’s best to drive your vehicle for a while before arriving for your smog test, since if your vehicle is running cold, the pollutant levels will be higher. However, if your vehicle still fails its test, keep in mind that emissions problems are generally inexpensive and quick to repair. If you believe your vehicle won’t pass a smog check, it may be best to go to a facility that can perform the check and make any necessary repairs and then re-test so the vehicle passes smog inspection.