What Wisconsin requires for emissions testing
Wisconsin requires emissions testing for most vehicles registered in the state, but the rules depend on where you live and what you drive. If you live in Dane County (Madison area) or Milwaukee County, your vehicle must pass an emissions test every two years as part of your registration renewal. Vehicles in other Wisconsin counties do not need emissions testing.
Diesel vehicles, motorcycles, and vehicles model year 1968 and older are exempt from testing statewide. Gasoline vehicles model year 1996 and newer in the testing counties must pass the test. Vehicles model year 1995 and older in those counties are also exempt.
The test itself checks your vehicle's on-board diagnostic system — a computer that monitors emissions equipment. The technician plugs a scanner into your vehicle's diagnostic port (usually under the steering wheel) and reads whether your emissions systems are working correctly. The test takes about 10 minutes and costs between $15 and $25, depending on the testing station.
Key Takeaways
- Only Dane County and Milwaukee County require emissions testing; other Wisconsin counties do not.
- Your vehicle must pass testing every two years when you renew your registration if you live in a testing county.
- Diesel vehicles, motorcycles, and vehicles older than 1968 or newer than 1996 (depending on fuel type) do not need testing.
- The test reads your vehicle's emissions computer and costs $15 to $25 at any state-certified testing station.
- A failed test means your emissions equipment needs repair before you can register your vehicle.
Where to get your vehicle tested in Wisconsin
You can have your vehicle tested at any Wisconsin Department of Safety and Professional Services (DSPS) certified emissions testing station. These include independent repair shops, dealerships, and some gas stations. The DSPS website lists all certified stations by county, and you can search by location to find one near you.
You do not need an appointment at most stations, but calling ahead can save you a wait. Bring your vehicle registration and driver's license. Some stations may ask for your vehicle identification number (VIN) before you arrive so they can look up your vehicle's test history.
Testing stations are open year-round, but many people wait until close to their registration renewal date. If you know your registration expires in a particular month, getting tested one to two months before that date gives you time to fix any problems if the test fails.
What happens if your vehicle fails the emissions test
A failed test means your vehicle's emissions equipment is not working as it should. The test report will tell you which system failed — usually the catalytic converter, oxygen sensor, or fuel system. You cannot renew your registration until you fix the problem and pass a retest.
Take the failed test report to a repair shop. The technician can read the same diagnostic codes your vehicle's computer stored and determine what needs repair. Some problems are straightforward and inexpensive (a loose gas cap, for example), while others like a faulty catalytic converter can cost several hundred dollars.
After repairs, return to any certified testing station for a retest. There is no additional fee for the retest itself, though you pay the testing station's standard fee again. Once you pass, you can complete your registration renewal.
How emissions testing connects to your registration renewal
In Dane and Milwaukee counties, you cannot renew your vehicle registration without a passing emissions test result. When you renew online or at a Wisconsin Department of Transportation (DOT) office, the system checks whether a current test is on file for your vehicle.
A current test means one performed within the past two years. If your test is older than two years or does not exist, your registration renewal will be blocked until you get tested. You can renew your registration online at dmv.wi.gov, by mail, or in person at any DOT service center.
Plan to get tested before your registration expires so you have time to fix any problems. If your registration has already expired and you have not been tested, you can still get tested and renew — there is no penalty for the delay, but you should not drive with an expired registration.
Understanding your emissions test report
Your test report shows whether your vehicle passed or failed and lists any diagnostic trouble codes if it failed. A passing report straightforward states that your vehicle's emissions systems are functioning within Wisconsin standards. You can print this report or have the testing station email it to you.
If you failed, the report lists the specific code — for example, "P0420 Catalyst System Efficiency Below Threshold" or "P0133 Oxygen Sensor Circuit." These codes tell a repair technician exactly which system to inspect. You do not need to understand the codes yourself; bring the report to your repair shop and they will use it to diagnose the problem.
Keep your passing test report until your next test is due. Some people take a photo of it on their phone in case they need proof for registration renewal or to show a potential buyer if they sell the vehicle.
What to do if you move to or from a testing county
If you move from a non-testing county to Dane or Milwaukee County, you will need to get your vehicle tested before your next registration renewal. If you move from a testing county to a non-testing county, you no longer need emissions testing, though you still need to renew your registration normally.
When you change your address with the Wisconsin DOT, update it at the same time you renew your registration. The system will then know which county you live in and whether testing is required. If you are unsure whether your new address is in a testing county, the DSPS website lists both counties by name.
Common reasons vehicles fail emissions testing
The most common failure is a faulty oxygen sensor, which monitors how much unburned fuel is in your exhaust. A loose or missing gas cap can also trigger a failure because it lets fuel vapors escape. Both of these are relatively inexpensive to fix.
A failing catalytic converter — the part that breaks down harmful emissions — is more expensive but also common in older vehicles. Engine misfires, a malfunctioning fuel injector, or problems with the evaporative emissions system (which captures fuel vapors) can also cause failures. If your check engine light is on, your vehicle is more likely to fail.
Regular maintenance helps prevent failures. Keep up with oil changes, use the fuel grade recommended in your owner's manual, and have any check engine light diagnosed promptly rather than waiting until your emissions test.
Frequently Asked Questions
Do I need emissions testing if I just bought a used car in Wisconsin?
If you are registering a used vehicle for the first time in Wisconsin and you live in Dane or Milwaukee County, you will need a passing emissions test before you can complete registration. If the vehicle was recently tested and passed, ask the seller for the test report — you may be able to use that result. Otherwise, get tested before your registration important date.
What if I cannot afford to fix my vehicle after it fails?
Wisconsin does not have a program that pays for emissions repairs. However, some nonprofit organizations and community action agencies offer low-cost repair information or can connect you with affordable repair shops. Contact your local community action agency or call 211 Wisconsin to ask about repair information programs in your area.
Can I test my vehicle in a different county than where I live?
Yes. You can get tested at any certified station in Wisconsin, even if it is not in your home county. The test result is valid for registration renewal regardless of where you were tested, as long as you live in Dane or Milwaukee County.
What happens if I drive without getting tested when I am required to?
Driving with an expired registration is a traffic violation. If you are stopped, you could receive a citation. The best approach is to get tested and renew your registration before your current registration expires, even if you are waiting for repairs.
How long does a passing emissions test stay valid?
A passing test is valid for two years from the date it was performed. You can renew your registration anytime during those two years, but you will need a new test after two years have passed.