What you need to know about Illinois emission tests

Illinois requires emission testing for most vehicles registered in Cook County and the collar counties (DuPage, Kane, Lake, McHenry, and Will). The test measures what comes out of your tailpipe to make sure your vehicle meets state air quality standards. You'll need to pass before you can renew your registration, and the test costs around $30 to $35 depending on the testing station.

The test itself takes about 10 to 15 minutes. A technician plugs a diagnostic machine into your vehicle's onboard computer port (located under the dashboard on the driver's side) and reads emissions data. You don't have to do anything except show up with your keys and registration. If your vehicle passes, you get a certificate that's valid for two years.

Not all of Illinois requires emission testing. If you live outside the five-county Chicago area, you don't need one. If you do live in a testing county and skip the test, you won't be able to renew your registration online or at the Secretary of State's office.

Key Takeaways

  • Emission testing is required only in Cook, DuPage, Kane, Lake, McHenry, and Will counties in Illinois.
  • The test costs $30 to $35 and takes 10 to 15 minutes at any state-certified testing station.
  • You must pass the test before renewing your vehicle registration in a testing county.
  • A passing certificate is valid for two years from the date of the test.
  • Vehicles newer than a certain model year may be exempt; check with your testing station about your vehicle's age.

Which vehicles need an emission test in Illinois

Most passenger cars, SUVs, and light trucks registered in the five-county area need a test. The main exemptions are vehicles that are too new or too old. Vehicles that are less than two model years old are exempt—so a 2024 vehicle registered in 2024 or 2025 doesn't need testing. Vehicles that are more than 25 model years old are also exempt.

Diesel vehicles have different rules. Diesel cars and light trucks must be tested, but only if they were manufactured after 1997. Diesel vehicles also have a higher emissions standard they must meet.

Electric vehicles and plug-in hybrids are exempt from emission testing in Illinois. If your vehicle is registered as an electric vehicle with the Secretary of State, you won't need a test.

If you're unsure whether your vehicle needs testing, call the testing station before you go. They can tell you based on your vehicle's year and type in less than a minute.

Where to find a testing station and what to bring

The Illinois Environmental Protection Agency maintains a list of certified testing stations on its website. You can search by county or zip code to find stations near you. Most are independent repair shops, not dealerships. Hours vary, but many are open early morning and evening to accommodate working drivers.

Bring your vehicle registration and a valid photo ID. The technician will need to see your registration to confirm your vehicle's details. You don't need an appointment at most stations—you can walk in—but calling ahead to check wait times is a good idea, especially on weekends.

The test must be done at a state-certified station. You cannot pass an emission test at a regular mechanic's shop or dealership unless they are certified by the state. The certification is displayed at the station.

What happens if your vehicle fails the emission test

If your vehicle fails, the testing station will give you a report showing which emissions standards it didn't meet. Common reasons for failure are a faulty oxygen sensor, a loose gas cap, a failing catalytic converter, or an engine problem that triggers the check engine light.

You have 30 days from the test date to get your vehicle repaired and retested at no additional charge at the same station. If you go to a different station, you'll pay the full testing fee again. Many stations will retest you for free if you return within 30 days of the original test.

If you can't afford repairs right away, you can request a waiver from the Illinois EPA. A waiver allows you to renew your registration without a passing test if you've spent at least $500 on repairs and the vehicle still fails. You'll need documentation of the repair attempts to request a waiver.

How to renew your registration after passing

Once you have a passing certificate, you can renew your registration online through the Illinois Secretary of State website, by mail, or in person at a local Secretary of State office. The certificate is valid for two years, so you won't need another test until your next renewal cycle.

If you renew online, you'll upload an image of your passing certificate or provide the certificate number. If you renew by mail or in person, bring the physical certificate with you. The Secretary of State's office will keep a copy.

Your registration renewal is separate from your emission test. You can take the test and renew your registration at different times, as long as you have a valid passing certificate when you renew.

Emission test requirements for used vehicle purchases

If you buy a used vehicle in Illinois, the seller must provide proof that the vehicle passed an emission test within the past 30 days. This is a state requirement, not optional. If the seller doesn't have a recent passing certificate, you'll need to get the vehicle tested before you can register it in your name.

Some private sellers may not know about this requirement. If you're buying from an individual, ask for the emission certificate before you complete the purchase. If the vehicle hasn't been tested recently, factor the $30 to $35 test cost into your negotiation.

Dealers are required to provide emission test certificates for all vehicles they sell. If a dealer doesn't have one, that's a red flag and you should ask why before buying.

Frequently Asked Questions

Can I get an emission test waiver if I can't afford to fix my vehicle?

Yes. If you've spent at least $500 on repairs and your vehicle still fails, you can request a waiver from the Illinois EPA. You'll need receipts or documentation of the repair work. The waiver lets you renew your registration for one year without a passing test, but you'll need to retest the following year.

What if my check engine light is on—will I automatically fail?

Not necessarily. The technician will read your vehicle's diagnostic codes, and some codes don't result in a test failure. However, certain codes related to emissions systems will cause a failure. Get the code read at a repair shop before testing if you're concerned.

How long is an emission test certificate valid?

A passing certificate is valid for two years from the date of the test. You can renew your registration anytime during those two years without needing another test. After two years, you'll need a new test to renew again.

Do I need an emission test if I'm registering a vehicle for the first time in Illinois?

Yes, if you're registering in a testing county. You'll need a passing emission test certificate before the Secretary of State will issue your registration. If you're moving from out of state, you have 30 days to get the test done.

What if I move out of a testing county—do I still need to test?

No. If you move to a county outside the five-county testing area, you won't need emission tests for future registrations. However, you'll still need a passing test to renew your current registration in the testing county before you move.