What Illinois emissions testing requires

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 area (Cook, DuPage, Kane, Lake, McHenry, or Will counties), you must test every two years. If you live elsewhere in Illinois, you must test every two years as well, but some older vehicles may be exempt.

The test itself checks whether your vehicle's exhaust meets state pollution standards. A technician will plug a diagnostic scanner into your car's onboard computer port (usually under the steering wheel) to read emissions data. The whole process takes about 10 to 15 minutes. Your vehicle must pass the test before you can renew your registration.

Vehicles that are too new or too old may not need to test. Generally, cars from the current model year and the previous four model years are exempt. Vehicles 25 years old or older are also exempt. Diesel vehicles, motorcycles, and some specialty vehicles have different rules, so check the Illinois Secretary of State website if your vehicle is unusual.

Key Takeaways

  • Illinois requires emissions testing every two years for most vehicles, regardless of where you live in the state.
  • The test takes 10 to 15 minutes and checks whether your exhaust meets state pollution standards using a diagnostic scanner.
  • Very new cars (current and previous four model years) and very old cars (25 years or older) are typically exempt from testing.
  • You can find approved testing stations through the Illinois Secretary of State website or by searching for "emissions testing near me" with your ZIP code.
  • A failed test usually means your vehicle has an emissions system problem that needs repair before you can renew registration.

Where to get tested in Illinois

The Illinois Secretary of State maintains a searchable list of approved emissions testing stations on its website. You can search by county or ZIP code to find stations near you. Most stations are independent repair shops, some are dealerships, and a few are dedicated testing-only facilities.

Testing stations set their own fees within state limits. Most charge between $15 and $30 for a basic test. Some stations offer additional services like emissions system repairs if your vehicle fails, which can be convenient but may cost more than taking your car elsewhere for repairs.

You do not need an appointment at most stations, but calling ahead is a good idea during busy times (late fall and early winter, when many people renew registrations). Bring your vehicle registration and a valid ID. The technician will need your vehicle identification number (VIN), which is on your registration or visible on the dashboard.

What happens if your vehicle fails the test

A failed test means your vehicle's emissions are above the state limit. Common reasons include a faulty oxygen sensor, a loose gas cap, a problem with the catalytic converter, or an engine misfire. The test report will tell you which emissions system is out of range, which helps a mechanic diagnose the problem.

You have 30 days from the test date to repair your vehicle and retest at no additional fee at the same station. If you repair it elsewhere, you can retest at any approved station, but you will pay the testing fee again. Keep your failed test report — you will need to show it when you retest.

If you cannot afford repairs right away, you can still renew your registration by paying a waiver fee, which is usually $20 to $30. The waiver lets you drive for one more registration cycle while you save for repairs. However, you will need to test again at your next renewal, and the vehicle must pass then.

Understanding your test results

A passing test means your vehicle met the state's emissions standards and you can renew your registration. The testing station will give you a receipt or printout showing that your vehicle passed. You do not need to bring this to the Secretary of State — the station reports the result electronically.

A failed test shows which pollutants are above the limit: usually nitrogen oxides (NOx), particulate matter, or hydrocarbons. The report will also show your vehicle's readiness status, which tells you whether the onboard diagnostic system has completed its self-checks. If the system is not ready, the vehicle may not have been driven enough since a repair or battery disconnect for the test to be valid.

Some stations offer a "pre-test" or diagnostic scan for a small fee before the official test. This can help you understand what might be wrong and whether repairs are worth attempting before the official test. It is optional but can save money if your vehicle is likely to fail.

Timing your test before registration renewal

You can test up to 120 days before your registration expires. Testing early gives you time to repair and retest if you fail, without rushing. Your registration renewal notice will show your expiration date and remind you that a passing test is required.

If your registration has already expired, you cannot legally drive your vehicle until you renew it, which requires a passing test. If you are in this situation, get tested as soon as possible and either repair and retest or pay the waiver fee to renew.

If you move to a different county in Illinois, your testing requirements do not change based on your new address until your next renewal. Your current registration is still valid until it expires, and you can test at any approved station in the state.

Special situations and exemptions

Vehicles registered as antiques or classics (usually 25 years or older) are exempt from testing. You must register them with the Secretary of State as antique vehicles, and they are typically allowed only limited use. Check the rules for your specific vehicle age and registration type.

Vehicles with a "check engine" light on will fail the test because the diagnostic system has detected a problem. You must have the problem diagnosed and repaired (or the code cleared by a mechanic) before testing. straightforward turning off the light without fixing the underlying problem will not help — the test will detect it again.

If you have a temporary registration or a recently purchased vehicle, you may have a grace period before your first test is due. The Secretary of State website lists the current rules for new registrations and transfers.

Preparing your vehicle for testing

Before you test, make sure your vehicle has been driven for at least 20 minutes at highway speeds within the past few days. This allows the onboard diagnostic system to complete its self-checks and gives you the best chance of passing. A vehicle that has just been started or driven only in stop-and-go traffic may show a "not ready" status and fail the test even if nothing is wrong.

Check that your gas cap is tight and in good condition. A loose or missing gas cap is one of the most common reasons for test failure and is also one of the cheapest to fix. If your check engine light is on, have it scanned before testing — you will fail regardless of other emissions levels.

Keep your vehicle well-maintained. Regular oil changes, air filter replacements, and spark plug service help keep emissions systems working properly. If your vehicle is older or has high mileage, consider a pre-test diagnostic scan to catch problems before the official test.

Frequently Asked Questions

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

Yes. You can test at any approved emissions testing station in Illinois, regardless of where your vehicle is registered. The station will report the result to the state electronically, and it will count toward your registration renewal.

What if I just had my vehicle repaired and the check engine light came back on?

The light may come back on if the repair did not fully resolve the problem, or if a new problem developed. Have the vehicle scanned again to see what code is present. You cannot test until the light is off and the underlying problem is fixed.

How long does a retest take if I failed the first time?

A retest takes the same 10 to 15 minutes as the original test. You have 30 days from your first test to retest at the same station for free. After 30 days, you must pay the testing fee again at any approved station.

Do I need to test if I only drive my car a few times a year?

Yes, unless your vehicle is exempt (very new, very old, or registered as antique). The testing requirement is based on registration, not on how much you drive. You must test to renew your registration, even if you drive rarely.

What happens if I move out of state but still have an Illinois registration?

You must still test to renew your Illinois registration, even if you live out of state. You can test at any approved station in Illinois, or you can transfer your registration to your new state and follow that state's rules instead.