What Colorado's emissions test measures and who needs it

Colorado requires an emissions test for most vehicles registered in the state, but the rules depend on where you live and what year your vehicle was made. The test measures what comes out of your tailpipe — specifically nitrogen oxides, particulate matter, and hydrocarbons — to confirm your vehicle meets state air quality standards.

You need an emissions test if you register a vehicle in an ozone nonattainment area, which includes the Denver metro area, parts of the Front Range, and a few other regions. Vehicles registered in rural Colorado may not need testing. The Colorado Department of Public Health and Environment maintains the current list of counties and areas that require testing.

Most gasoline vehicles model year 1981 and newer must test. Diesel vehicles model year 1997 and newer must test. Electric vehicles, motorcycles, and vehicles under 8,500 pounds registered as recreational are exempt. Vehicles that are brand new to the state (first registration) are exempt for that first year.

Key Takeaways

  • Colorado emissions testing is required in ozone nonattainment areas like the Denver metro region, but not statewide, and you can find your area's requirement on the state health department website.
  • The test itself takes about 10 minutes at a licensed testing station and costs between $20 and $30, depending on the station.
  • Your vehicle must pass before you can renew your registration, and you have until your registration expiration date to complete the test.
  • If your vehicle fails, you have 60 days to repair it and retest at no additional charge, or you can dispute the results within 30 days.
  • You can find testing stations through the Colorado Department of Public Health and Environment's online locator or by calling your county clerk's office.

How to find a testing station and what to bring

The Colorado Department of Public Health and Environment runs an online station locator at cdphe.colorado.gov where you enter your county and see all licensed testing facilities near you. You can also call your county clerk's office — they maintain lists of stations in your area and can tell you which ones have the shortest wait times.

Bring your vehicle registration and a valid photo ID. The station will need to see proof that your vehicle is registered. If you are testing a vehicle you just bought, bring the bill of sale or title transfer paperwork. Some stations accept walk-ins; others require appointments. Call ahead to confirm hours and whether you need to book a time slot.

Your vehicle should be in normal operating condition — the engine should be warmed up but not overheated. Do not arrive with a cold engine or one that has been running for only a minute or two. The test itself takes about 10 minutes and involves driving on a dynamometer (a treadmill-like device) while the machine reads your emissions.

Test costs and what happens if you pass or fail

A single emissions test costs between $20 and $30 at most Colorado stations, though prices vary slightly. Some stations charge a few dollars more for diesel vehicles. You pay at the station when you take the test — there is no online payment or advance fee.

If your vehicle passes, you receive a certificate or pass notice on the spot. The station sends the results electronically to the Colorado Department of Revenue, and your registration renewal can proceed. You do not need to bring the certificate to the DMV; the state receives the results automatically.

If your vehicle fails, you have 60 days from the test date to repair the vehicle and retest at no charge. The station gives you a failure notice listing the specific emissions that were too high. You do not need to return to the same station for your retest — any licensed station in Colorado will accept your retest. If you believe the test was wrong, you can request a retest dispute within 30 days of the failure; contact the Colorado Department of Public Health and Environment for the dispute process.

When your test is due and what happens if you miss the important date

Your emissions test must be completed by your vehicle registration expiration date. You can take the test up to 90 days before your registration expires, so plan ahead if you know your registration is coming due. The test result is valid for two years from the date you take it.

If you do not complete the test by your expiration date, you cannot legally renew your registration. The Colorado Department of Revenue will not process a renewal without a passing emissions result for vehicles in testing areas. You can still take the test after your registration expires, but you will be driving with an expired registration, which is a traffic violation.

If you are moving out of a testing area or selling your vehicle, you do not need to test if your registration expires before you complete the move or sale. Bring proof of the move or a bill of sale to your county clerk's office to explain why the test was not done.

What to do if your vehicle fails the test

A failure usually means your vehicle has an emissions system problem — often a faulty oxygen sensor, catalytic converter issue, or engine control problem. The failure notice will tell you which emissions were high. Take this notice to a mechanic who can diagnose the specific problem.

Common repairs include replacing the oxygen sensor, fixing a vacuum leak, or addressing a check engine light. Some repairs are inexpensive (under $100), while others can cost several hundred dollars. Before spending money, ask your mechanic whether the repair is worth it compared to the vehicle's value.

After repair, return to any licensed testing station for your retest. You have 60 days and do not pay again. If the vehicle still fails after repair, you can request another 60-day extension by contacting the Colorado Department of Public Health and Environment, though extensions are not automatic.

Emissions testing for vehicles with check engine lights

If your check engine light is on, your vehicle will likely fail the emissions test. The light indicates a problem in the emissions system, and the test measures whether that system is working properly. Do not take the test until the light is off.

Have a mechanic read the diagnostic code (this often costs $50 to $100 or is free at some shops). Fix the underlying problem, clear the code, and drive the vehicle for at least 100 miles so the system can relearn and confirm the fix. Then take the test.

If you take the test with the check engine light on and fail, you still have 60 days to repair and retest. But you will lose time if you did not address the light first. Plan your repair timeline so the light is off before you test.

Frequently Asked Questions

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

Yes. You can take the test at any licensed station in Colorado, regardless of which county issued your registration. The results are reported to the state and linked to your vehicle's registration number, so the county does not matter.

What if I just bought a used vehicle and it failed its last test?

The previous owner's test results do not transfer to you. You will need to take a new test before you can register the vehicle in your name. If the vehicle failed recently, have a mechanic inspect it before you buy it, or negotiate the purchase price to account for likely repairs.

Do I need an emissions test if I am only renewing my registration online?

Yes. Online renewal still requires a passing emissions test result on file. You must complete the test before you can renew, whether you renew online or in person at the county clerk's office.

What happens if I move to Colorado with a vehicle registered in another state?

When you register your out-of-state vehicle in Colorado, you will need an emissions test if you are moving to a testing area. The test must be completed before the registration is finalized. Some county clerk offices will let you schedule the test before you register; call ahead to ask about the process in your county.

Can I dispute a test result if I think the station made a mistake?

Yes. You have 30 days from the test date to request a dispute. Contact the Colorado Department of Public Health and Environment with your test results and the reason you believe the result was wrong. They will review your case and may authorize a free retest at a different station.