What Illinois requires for emission testing

Illinois requires emission testing for most vehicles registered in the state, though the exact requirement depends on the vehicle's age, type, and where you live. Vehicles model year 1996 and newer must pass an emission test every two years as part of the registration renewal process. Diesel vehicles, motorcycles, and vehicles registered outside Illinois are generally exempt.

The state divides Illinois into two testing regions: the Chicago area (Cook, DuPage, Kane, Lake, McHenry, and Will counties) and the rest of the state. The Chicago region has stricter standards because it does not meet federal air quality targets. Vehicles in the Chicago region must pass both a tailpipe emissions test and an onboard diagnostic (OBD) test, while vehicles in other parts of Illinois only need the OBD test.

You cannot register or renew your vehicle registration without a passing emission test result on file with the Illinois Secretary of State. The test must be completed within 30 days before your registration expires. If your vehicle fails, you have until your registration expiration date to repair it and retest at no additional fee.

Key Takeaways

  • Illinois requires emission testing every two years for vehicles model year 1996 and newer, with the test due within 30 days before your registration expires.
  • The Chicago region (six counties) requires both tailpipe and OBD testing; the rest of Illinois requires only OBD testing.
  • You must use an Illinois-licensed emission testing station, which you can find through the Secretary of State's website or by searching for "emission test" plus your city name.
  • A single failed test does not prevent registration renewal; you have until your expiration date to repair and retest at the same station for free.
  • The test costs between $15 and $30 depending on the station, and results are sent directly to the Secretary of State's database.

Where to get tested in Illinois

Illinois operates through a network of privately owned, state-licensed emission testing stations rather than a single government facility. You can find stations near you by visiting the Illinois Secretary of State's website and using their station locator tool, or by searching online for "emission test" plus your city or zip code. Most stations are independent repair shops, quick-lube facilities, or dedicated testing centers.

Not every repair shop is licensed to perform emission testing. Before you go, confirm that the station holds an active Illinois emission testing license. The station should display this license visibly, and you can verify it through the Secretary of State's database if you have the station's name or license number.

Testing stations set their own prices within state limits. The cost typically ranges from $15 to $30 per test. Some stations may charge extra for retests if you fail, though state rules allow one free retest at the same station within 30 days of a failure. Call ahead to ask about pricing and whether they accept walk-ins or require an appointment.

The testing process and what happens during the exam

When you arrive at a testing station, bring your vehicle keys and a valid photo ID. The technician will ask for your vehicle identification number (VIN) and may ask when you last had the vehicle serviced. The entire test usually takes 10 to 20 minutes.

In the Chicago region, the technician will connect a probe to your vehicle's tailpipe to measure emissions directly, then plug a diagnostic scanner into your onboard diagnostic port (usually located under the steering wheel or dashboard) to read your vehicle's computer for emission-related fault codes. In the rest of Illinois, only the OBD scan occurs. The vehicle must be running and warmed up for accurate results.

You will receive a printed receipt showing whether you passed or failed. If you passed, the result is automatically sent to the Secretary of State's database and appears in your registration record within one business day. If you failed, the receipt will show which emissions standard your vehicle did not meet, such as nitrogen oxides or particulate matter. You can then take this information to a mechanic to help diagnose the problem.

What causes a vehicle to fail the emission test

The most common reason for failure is a check engine light that is on or has been triggered recently. The light indicates that your vehicle's onboard computer has detected a problem with the engine, emissions system, or transmission. Even if the light is not currently on, if the computer has stored a fault code related to emissions, the vehicle will fail the OBD portion of the test.

Other frequent causes include a faulty oxygen sensor, a malfunctioning catalytic converter, a loose or damaged gas cap, or a problem with the fuel injection system. Older vehicles or those with high mileage are more likely to fail because emission control components wear out over time. Vehicles that are not regularly maintained, such as those that have skipped oil changes or have not had spark plugs replaced, also fail more often.

If your vehicle fails, the test receipt will show the specific fault code. You can search this code online or give it to a mechanic to understand what needs repair. Many repairs are relatively inexpensive — a gas cap replacement might cost $10 to $20, while an oxygen sensor replacement typically costs $100 to $300. More complex repairs, such as catalytic converter replacement, can cost $500 or more.

Retesting after a failure and registration important date

If your vehicle fails, you do not lose your registration when ready. You have until your registration expiration date to repair the vehicle and retest. During this time, you can still drive the vehicle legally. Many stations allow one free retest within 30 days of the initial failure, so you do not pay twice if you fix the problem and come back.

After you repair the vehicle, return to the same testing station (or any licensed station) and request a retest. Bring your original test receipt if possible, as it helps the technician understand what was previously flagged. The retest follows the same process as the initial test and takes the same amount of time.

If you do not retest before your registration expires, your registration will lapse and you cannot legally drive the vehicle. You will need to pass the emission test before you can renew your registration with the Secretary of State. If your registration has already expired, you will also owe a late renewal fee in addition to the registration renewal cost.

Emission testing for vehicles registered outside Illinois

If you own a vehicle registered in another state but live in Illinois, you do not need to pass an Illinois emission test as long as your vehicle remains registered out of state. However, if you move to Illinois permanently or change your vehicle's registration to Illinois, you must then follow Illinois emission testing rules.

When you register a vehicle in Illinois for the first time, the Secretary of State will not require an emission test result for that initial registration. You will first need to pass a test when you renew that registration two years later. This grace period gives you time to address any emission issues before the test is required.

Frequently Asked Questions

Can I test my vehicle before my registration expires?

Yes. You can test your vehicle anytime within 30 days before your registration expires. The test result is valid for two years from the date you pass it, so if you test early, your next test will not be due until two years after that test date, not two years after your registration renewal date.

What if I move to a different region of Illinois after I pass the test?

Your test result remains valid for two years regardless of where you move within Illinois. If you move from the Chicago region to another part of the state, you do not need to retest. The same applies if you move from another region into the Chicago area — your existing test result is still good until it expires.

Do I need emission testing if my vehicle is brand new?

No. New vehicles are exempt from emission testing for their first two years of registration. You will first need to pass a test when you renew your registration for the second time. Vehicles model year 1995 and older are permanently exempt from Illinois emission testing.

What happens if I fail the test twice?

You can retest as many times as needed before your registration expires. Each failed test does not prevent you from trying again. However, if your registration expires before you pass, you must pass the test before you can renew your registration with the Secretary of State. There is no limit on the number of attempts.

Can I get a waiver if my vehicle fails the emission test?

Illinois does not offer emission test waivers based on repair costs or hardship. However, if your vehicle has a mechanical problem that prevents it from being tested safely — such as a broken transmission — some stations may issue a conditional pass that allows you to register the vehicle while you arrange repairs. Contact your testing station to ask whether this option is available in your situation.