What Illinois requires and who has to test

Illinois requires emissions testing for most gasoline-powered vehicles registered in the state, with a few exceptions. Your vehicle needs a test if it is registered in Cook County (which includes Chicago) or in the collar counties of DuPage, Kane, Lake, McHenry, or Will. Vehicles registered elsewhere in Illinois do not need emissions testing.

Diesel vehicles, motorcycles, and vehicles that are less than two model years old are exempt from testing. If your vehicle is registered in one of the required counties and is older than two model years, you will need to complete a test before you can renew your registration.

The test itself checks whether your vehicle's emissions fall within state limits. Illinois uses the IM240 test, which measures what comes out of your tailpipe while your car runs on a dynamometer — a machine that simulates driving conditions. The test takes about 10 minutes and costs between $25 and $35, depending on the testing station.

Key Takeaways

  • Illinois requires emissions testing only in Cook County and the five surrounding collar counties; vehicles registered elsewhere do not need testing.
  • Your vehicle must pass an IM240 test, which measures tailpipe emissions while the car runs on a dynamometer, and costs $25 to $35.
  • You can find a testing station through the Illinois Environmental Protection Agency website or by calling 1-800-253-2000.
  • Test results are sent electronically to the Secretary of State, so you do not need to bring paperwork to your registration renewal.
  • If your vehicle fails, you have 30 days to repair it and retest at no additional cost at the same station.

Finding a testing station and scheduling

The Illinois Environmental Protection Agency (IEPA) maintains a list of licensed testing stations on its website. You can search by county or zip code to find stations near you. Most stations are independent repair shops, not dealerships, and many offer walk-in testing during business hours.

Call ahead before you go. Some stations have wait times during peak hours, and a few require appointments. Testing stations are open year-round, but many close on Sundays and some close on Mondays, so check hours before you drive there.

Bring your vehicle registration and a valid photo ID. You do not need to bring your title or proof of insurance. The testing station will look up your vehicle information using your license plate number and registration.

What happens during the test and what results mean

When you arrive, the technician will inspect your vehicle's exterior — checking that your tailpipe is intact, your gas cap is present, and your check engine light is not on. If any of these fail the visual inspection, your vehicle cannot be tested that day and you will need to repair it first.

If your vehicle passes the visual inspection, the technician will drive it onto the dynamometer. The machine accelerates and decelerates your car while measuring emissions from your tailpipe. The entire test takes about 10 minutes. You will receive a printed receipt showing whether you passed or failed.

A pass means your emissions are within state limits. The result is sent electronically to the Secretary of State within 24 hours, and you can renew your registration when ready. A fail means your emissions exceeded the limit. You have 30 days to repair your vehicle and return to the same testing station for a retest at no charge.

Repairs and retesting after a failure

If you fail the test, the receipt will show which emissions category exceeded the limit — usually nitrogen oxides, particulate matter, or hydrocarbons. This information helps a mechanic diagnose the problem, though it does not pinpoint the exact cause.

Common reasons for failure include a faulty oxygen sensor, a clogged fuel injector, worn spark plugs, or a problem with the catalytic converter. A mechanic can run a diagnostic scan using your vehicle's onboard computer to narrow down the issue. Repairs can range from $50 for spark plugs to $800 or more for a catalytic converter.

You have 30 days from the test date to complete repairs and return to the same testing station for a free retest. Bring your original test receipt. If you pass the retest, the result goes to the Secretary of State and you can renew your registration. If you fail again, you have another 30 days to repair and retest.

Timing for registration renewal

Your vehicle registration expires on a date printed on your registration card. You must pass an emissions test before that date to renew. The test result is valid for 120 days, so you can test up to four months before your registration expires.

If your registration expires before you pass a test, your vehicle is no longer legal to drive. You cannot renew your registration without a passing test result. If you are in this situation, you will need to test and pass before you can drive legally again.

Plan to test at least two weeks before your registration expires. This gives you time to repair and retest if you fail the first time. If you fail twice and are running out of time, contact a mechanic when ready — some shops offer expedited diagnostics for vehicles that have failed emissions tests.

What to do if your vehicle repeatedly fails

If your vehicle fails the test twice within 30 days, you may be may be able to access for the Repair information Program, which helps pay for emissions-related repairs. The program covers up to $500 toward repairs if your household income is at or below 200 percent of the federal poverty line. Contact the IEPA at 1-800-253-2000 to learn whether you may have access to and which repair shops participate in the program.

If repairs are not economically feasible — meaning the cost of repairs exceeds the vehicle's value — you may be able to get a waiver. A waiver allows you to renew your registration without a passing test, but only after you have failed twice and attempted repairs. You must request a waiver through the Secretary of State's office.

Frequently Asked Questions

What if my check engine light is on?

Your vehicle will fail the visual inspection and cannot be tested. You must have the check engine light diagnosed and repaired first. Once the light is off, you can return for testing. The light indicates a problem with your emissions system, so fixing it usually improves your chances of passing the test.

Can I test in a different county than where my vehicle is registered?

No. You must test at a station in the county where your vehicle is registered. If you live in Cook County but your vehicle is registered in a collar county, you must test in that collar county. If your vehicle is registered outside the testing area, you do not need to test at all.

How long does it take to get my test result?

You receive a printed receipt when ready after the test. The result is sent electronically to the Secretary of State within 24 hours. You can renew your registration as soon as you have the printed receipt — you do not need to wait for the electronic transmission.

What if I move out of the testing area?

Once you register your vehicle in a county outside the testing area, you no longer need emissions testing. However, you must pass a test before you can renew your registration in your current county. After that renewal, future renewals in your new county will not require testing.

Can I test my vehicle early before my registration expires?

Yes. You can test up to 120 days before your registration expires. The test result is valid for that entire 120-day period, so you can renew your registration anytime after you pass. Testing early gives you time to repair and retest if you fail.