What Illinois requires for emissions testing

Illinois requires emissions testing for most vehicles registered in the state, but the rules depend on where you live and how old your car is. If you live in the Chicago metropolitan area — Cook, DuPage, Kane, Lake, McHenry, or Will County — your vehicle must pass an I/M 240 test, which measures tailpipe emissions under load on a dynamometer. If you live elsewhere in Illinois, you need a OBDII test, which reads your vehicle's onboard diagnostic system for emissions-related faults. Vehicles newer than the current model year are exempt. Diesel vehicles, motorcycles, and vehicles registered as salvage or non-operation are also exempt.

The test is required every two years when you renew your vehicle registration, unless your vehicle is brand new or you have a valid exemption. You must pass the test before your registration expires, and the test result is valid for two years from the date you take it.

Key Takeaways

  • Chicago-area counties (Cook, DuPage, Kane, Lake, McHenry, Will) require the I/M 240 dynamometer test; all other Illinois counties require the OBDII onboard diagnostic test.
  • You must pass emissions testing every two years when you renew your registration, and the test result is valid for exactly two years from the test date.
  • You can take the test at any licensed emissions testing station in Illinois, and you do not have to test in the county where you live.
  • If your vehicle fails, you have 30 days to repair it and retest at no additional charge at the same station.
  • Vehicles newer than the current model year, diesel vehicles, and motorcycles are exempt from testing.

Where to find a testing station and what to bring

You can locate a licensed emissions testing station through the Illinois Environmental Protection Agency website, which maintains a searchable list of all approved stations statewide. You do not have to test in your home county — you can drive to any licensed station in Illinois. Testing stations are typically run by repair shops, quick-lube facilities, and dedicated inspection centers, and most can fit you in without an appointment, though calling ahead during busy seasons is wise.

Bring your vehicle registration or proof of ownership and a valid photo ID. Your vehicle's engine should be at normal operating temperature when you arrive, so drive it for at least 10 to 15 minutes before the test. If your check engine light is on, the vehicle will fail the test automatically, so have that diagnosed before you go.

How the I/M 240 test works in the Chicago area

The I/M 240 test places your vehicle on a dynamometer — a machine with rollers that simulate driving — and measures emissions while your car accelerates under load. The test takes about 10 minutes and simulates city and highway driving. Your vehicle must meet specific limits for nitrogen oxides (NOx), particulate matter, and hydrocarbons. The test is more stringent than the OBDII test because the Chicago area has historically struggled with air quality.

If your vehicle passes, you receive a certificate valid for two years. If it fails, the testing station will print a report showing which emissions exceeded the limit. You then have 30 days to have the vehicle repaired and retested at the same station at no additional charge. If you fail a second time, you can take it to a different station, but you will pay the full testing fee again.

How the OBDII test works in the rest of Illinois

The OBDII test is simpler and faster than the I/M 240. The technician plugs a diagnostic scanner into your vehicle's onboard diagnostic port — usually located under the steering wheel — and reads the emissions system for faults. The test checks whether your catalytic converter, oxygen sensors, and emissions control system are functioning and whether any emissions-related trouble codes are stored in your vehicle's computer. The entire test takes about 5 minutes.

Your vehicle passes if no emissions-related codes are present and your system is ready for testing. If your vehicle has not been driven enough since a repair or battery disconnect, the system may not be ready, and you will fail the test. In that case, drive the vehicle for at least 100 to 200 miles of mixed city and highway driving, then retest. Like the I/M 240, you have 30 days to repair and retest at no additional charge if you fail.

What happens if your vehicle fails

A failed test does not mean your registration is automatically suspended, but you cannot renew your registration without a passing test result. If your registration expires before you pass, you cannot legally drive the vehicle. You have 30 days from the test date to repair the vehicle and retest at the same station for free. The testing station will give you a written report showing what failed and what repairs are likely needed.

Common reasons for failure include a faulty oxygen sensor, a failing catalytic converter, a loose gas cap (OBDII test), or a malfunctioning emissions control valve. These repairs range from $50 for a gas cap to $800 or more for a catalytic converter. If you cannot afford repairs, some repair shops offer payment plans, and some nonprofits in Illinois offer vehicle repair information for low-income drivers — contact your local community action agency to ask.

Timing and registration renewal

You must pass the emissions test before your registration renewal date. The test result is valid for two years from the date you take it, so you can test up to 60 days before your registration expires. If you test early, your two-year validity period begins on the test date, not on your registration renewal date. Plan to test at least two weeks before your registration expires to leave time for repairs if you fail.

When you renew your registration online or at a Secretary of State facility, you will be asked to provide your test result number or confirm that you have passed. If you do not have a passing result on file, your registration will not be processed. Some testing stations report results electronically to the state, but others require you to bring the paper certificate to the Secretary of State office or upload it yourself during online renewal.

Exemptions and special cases

Vehicles registered as non-operation, salvage, or antique are exempt from emissions testing. Vehicles that are fewer than 4 model years old are also exempt — for example, a 2024 vehicle registered in 2024 does not need to test until 2026. If you have a vehicle with a disability license plate, you may be exempt; contact your local Secretary of State office to confirm. Vehicles powered entirely by electricity are exempt because they produce no tailpipe emissions.

If you are moving to Illinois from another state, your vehicle must pass an Illinois emissions test before you can register it in the state. If you are moving out of Illinois, you do not need a current Illinois test result to sell or transfer the vehicle.

Frequently Asked Questions

Can I test my vehicle before my registration expires?

Yes. You can test up to 60 days before your registration renewal date. The test result is valid for two years from the test date, so if you test early, your validity period begins on that earlier date, not on your renewal date. Plan ahead so you have time to repair and retest if needed.

What if I move to a different county in Illinois?

If you move from a non-Chicago county to the Chicago area, your next test will be the I/M 240 test. If you move from the Chicago area to another county, your next test will be the OBDII test. You do not need to retest when ready; you test according to your registration renewal date and your new county's requirements.

Do I have to repair my vehicle at the testing station?

No. You can take your vehicle to any repair shop you choose. The testing station will give you a report of what failed, and you can use that to get a quote from a mechanic elsewhere. You have 30 days to repair and retest at the same station for free, but you can use a different repair shop in between.

What if my vehicle is too old to pass?

If your vehicle is very old and cannot pass even after repairs, you may not be able to renew your registration in Illinois. Some older vehicles can be registered as non-operation, which exempts them from testing but restricts where you can drive them. Contact your local Secretary of State office about your options.

Can I test in a different county than where I live?

Yes. You can test at any licensed emissions testing station in Illinois, regardless of where your vehicle is registered. This is useful if you live near a county border or if a station near you is busy.