Vehicle emissions have a lot of negative effects on the environment. Modern emissions laws try to ensure vehicles today have cleaner emissions than ever. One way to monitor this is through emissions testing.
What Is Emissions Testing?
Emissions testing, also known as smog testing, measures your vehicle’s emissions and the accuracy of the onboard computer when tracking the pollutants the vehicle is releasing. The tests review the levels of carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and other gases that your vehicle produces.
Licensed inspection stations for emissions testing can be found in select repair shops and dealerships, as well as dedicated emissions testing centers.
Why Do Vehicles Need Emissions Tests?
Emissions tests are often mandatory in particularly polluted areas to ensure the air quality doesn’t continue to deteriorate. The US government implemented the Clean Air Act in 1990, which set pollution-level requirements for states and local municipalities. The areas that didn’t reach these requirements were ordered to implement mandatory vehicle emissions testing as a result.
Emissions testing or smog testing measures your vehicle’s emissions and the accuracy of the onboard computer when tracking the pollutants the vehicle is releasing.
Types of Emissions Tests
There are different types of emissions tests out there, and states with emissions testing often have different types available. However, these two particular tests are the most common and will show up in most states:
Onboard Diagnostic (OBD ) Inspection
The OBD II inspection is usually conducted on vehicles made from 1996 onwards. This test takes information from your vehicle’s internal emissions diagnostic system and verifies its accuracy. It also makes sure the onboard computer isn’t flagging any problems in the emissions systems or the related components.
Acceleration Simulation Mode (ASM) Test
The ASM test is a type of tailpipe test conducted on older vehicles manufactured from 1995 and earlier. It’s also used for vehicles without an OBD-II installed. During the test, a tailpipe sensor is used alongside a dynamometer, which is basically a treadmill for cars. The vehicle then runs at a steady speed while its emissions are measured. The acceptable limits for these emissions are adjusted based on the weight of the vehicle.
What States Require Emissions Testing?
Now, you’ll likely notice that there are a number of states without required emissions testing in their laws. You can find out what states require smog tests here:
State
Requirement
Alabama
Select cities and municipalities only
Alaska
Not required
Arizona
Initial registration for drivers residing in or commuting into Tucson and Phoenix
Annually for registration renewal for drivers residing in or commuting into Tucson and Phoenix
Every two years in counties under the Automobile Inspection and Readjustment (AIR) Care Program
Connecticut
Every other year
Delaware
Biannually
When acquiring a new vehicle title
Florida
Not required
Georgia
Annually in select counties for gasoline cars or light-duty trucks (weighing 8,500 lbs or less) made between 1994 and 2014
Hawaii
Not Required
Idaho
Before registration in the Treasure Valley Airshed (City of Kuna and Ada and Canyon counties)
Illinois
Select municipalities that don’t meet federal air quality standards
Indiana
Initial registrations
Biannually for vehicle owners in Porter and Lake counties
Iowa
Not required
Kansas
Not required
Kentucky
Not required
Louisiana
Every two years for vehicles in certain parishes and cities
Vehicles of new Louisiana residents
Vehicles with a break tag or emission sticker about to expire
Upon registration with the Office of Motor Vehicles
When ordered by a Louisiana law enforcement officer
Maine
Required for residents of Cumberland County
Maryland
Vehicles of new Maryland residents
Every two years for all Maryland-registered vehicles
Massachusetts
Annually
Michigan
Not required
Minnesota
Not required
Mississippi
Not required
Missouri
Every two years for gasoline vehicles made in 1996 or later and diesel vehicles made in 1997 or later that weigh under 8,500 lbs
Every time the vehicle’s title is transferred
Montana
Not required
Nebraska
Not required
Nevada
Initial registration
Annually for registration renewal
New Hampshire
Initial registration
Annually for registration renewal
New Jersey
Every two years and for initial registrations
New Mexico
Annual and initial registration in Bernalillo County
New York
Initial registration
Annually for registration renewal
North Carolina
Vehicles in certain counties before their registration renewal deadline
North Dakota
Not required
Ohio
Every two years for certain counties
Oklahoma
Not required
Oregon
Every two years for vehicle owners in Portland and Medford
Pennsylvania
Initial registration
Rhode Island
Within 5 days of original registration
Every two years for gasoline passenger vehicles that weigh less than 8,500 lbs
South Carolina
Not required
South Dakota
Not required
Tennessee
Initial registration in select counties
Annually before registration renewal in select counties
Texas
Annually in select counties and areas
Utah
Every two years in select counties for vehicles less than six years old
Annually before registration in select counties for vehicles more than six years old
Vermont
Initial registration
Annually for registration renewal
Virginia
Initial registration in select counties and cities
Every two years for registration renewal in select counties and cities
Washington
Initial registration for certain vehicles in select counties
Every two years for certain vehicles in select counties
Washington DC (District of Columbia)
Initial registration
Every two years for registration renewal for vehicles made in 1968 and later
Annually for most commercial and free-for-hire vehicles
West Virginia
Not required unless part of the annual safety inspection
Wisconsin
Initial registration and every two years for registration renewal
Wyoming
Not required
As you can see, there are still a good number of states without smog check laws in place. Those that do have these laws often require that the checks be conducted around a vehicle’s registration period. Be sure to check the rules in your area to make sure you aren’t missing any required tests.
Lisa Conant grew up in Canada around a solid contingency of gear heads and DIY motor enthusiasts. She is an eclectic writer with a varied repertoire in the automotive industry, including research pieces with a focus on daily drivers and recreational vehicles. Lisa has written for Car Bibles and The Drive.
The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.
