What Colorado's emission test covers and who needs one

Colorado requires an emission test every two years for most vehicles registered in the state, with a few exceptions. The test measures what comes out of your tailpipe — carbon monoxide, nitrogen oxides, and particulate matter — to confirm your vehicle meets state air quality standards. You'll need one before you can renew your registration, and the test must happen within 90 days of your registration expiration date.

You do not need an emission test if your vehicle is a diesel truck registered for over 14,000 pounds, a motorcycle, a vehicle that is less than six model years old (with some exceptions), or a vehicle that is registered as non-operational. If you are unsure whether your vehicle is exempt, the Colorado Department of Revenue website lists the full exemption rules by vehicle type and year.

The test itself takes about 10 to 15 minutes. A technician will plug a diagnostic scanner into your vehicle's onboard computer and run it through a series of idle and acceleration tests. If your vehicle passes, you get a certificate that your registration renewal office will accept. If it fails, you have 30 days to repair the vehicle and retest at no additional charge.

Key Takeaways

  • Colorado requires emission testing every two years for most vehicles before registration renewal, with the test valid for 90 days before your registration expires.
  • Vehicles less than six model years old, motorcycles, and heavy diesel trucks are exempt from testing.
  • You can find a testing station through the Colorado Department of Revenue's online locator or by calling your county air pollution control division.
  • If your vehicle fails, you have 30 days to make repairs and retest for free at the same station.
  • The test costs between $25 and $35 depending on the testing station, and you must bring your vehicle registration and proof of insurance.

Where to find a testing station in Colorado

Colorado has two types of emission testing stations: state-certified private stations and county-run facilities. Private stations are scattered across the state and often have shorter wait times. County facilities are run by local air pollution control divisions and are typically less expensive, though they may have longer lines during peak renewal periods.

The fastest way to find a station near you is the Colorado Department of Revenue's online station locator at the CDOR website. You can search by county or zip code and see which stations are open, their hours, and whether they accept walk-ins or require appointments. Many private stations now offer online booking, which can save you time during busy months like September and October.

If you cannot find a station online or prefer to call, contact your county's air pollution control division directly. They can tell you which stations are currently operating and how long the wait typically is on the day you plan to visit.

What to bring and what the test costs

Bring your vehicle registration and proof of insurance. Some stations may also ask for your driver's license. The test itself costs between $25 and $35 depending on which station you use — private stations set their own fees, while county facilities have a standard rate set by the state.

If your vehicle fails the test, you do not pay again to retest. You have 30 days to repair the problem and return to the same station for a free retest. If you go to a different station, you may have to pay the full fee again, so plan to return to the same location.

Some repair shops offer a "pre-test" for a small fee to check whether your vehicle will pass before you go to the official testing station. This is optional but can save you time if you suspect your vehicle may fail.

What happens if your vehicle fails the emission test

A failed test means your vehicle is emitting pollutants above Colorado's limits. The test report will tell you which pollutants are out of range — usually carbon monoxide, nitrogen oxides, or particulate matter — but it will not tell you what is wrong with your vehicle. That diagnosis is up to you and a mechanic.

Common reasons for failure include a faulty oxygen sensor, a clogged fuel injector, a bad catalytic converter, or an engine timing problem. A mechanic can run their own diagnostic scan to pinpoint the issue. If the repair is expensive, you may want to get a second opinion before proceeding.

After you repair the vehicle, return to the same testing station within 30 days for a free retest. Bring your repair receipt if the station asks for it — some do, some do not. If the vehicle passes on the retest, you can proceed with your registration renewal.

Emission testing important date and registration renewal

Your emission test is valid for 90 days before your registration expires. For example, if your registration expires on December 31, you can test anytime from October 3 onward. Testing too early means your certificate may expire before you renew your registration, and you will have to test again.

You must have a passing emission test certificate before you can renew your registration. If your registration has already expired and you have not tested, you cannot legally drive the vehicle. If you are close to your expiration date and worried about wait times, test early enough to leave room for a retest if needed.

If you move out of Colorado or sell your vehicle, you do not need to complete an emission test. If you move into Colorado, you will need to test before you can register your vehicle in the state.

Special cases: Diesel vehicles, new vehicles, and out-of-state transfers

Diesel trucks registered for over 14,000 pounds are exempt from emission testing in Colorado. Light-duty diesel vehicles (under 14,000 pounds) must test like gasoline vehicles. If you own a diesel truck and are unsure of your registration weight, check your registration documents or contact your county assessor's office.

Vehicles less than six model years old do not need to test. A 2019 vehicle does not need to test until 2025, for example. Once your vehicle reaches six model years old, you will need to test every two years after that. Hybrid and electric vehicles are also exempt from testing.

If you are registering a vehicle in Colorado for the first time and it is from out of state, you will need an emission test before you can complete the registration. The test must be done at a Colorado station, so plan to test after you arrive in the state but before you go to the DMV.

What to do if you cannot pass the test

If your vehicle repeatedly fails the test even after repairs, you may be dealing with a serious engine problem. At that point, it is worth getting a second mechanic's opinion or consulting a shop that specializes in emissions repairs. Some shops offer a "no pass, no pay" may provide where they will not charge you if the vehicle still fails after their repair.

Colorado does not have a "clunker buyback" program or a way to waive the emission requirement for older vehicles. If your vehicle cannot pass and repairs are too expensive, your only option is to replace the vehicle or stop registering it in Colorado.

If you believe the test was run incorrectly, you can request a retest at a different station. Keep your original test report and bring it with you. The second station can review the results and tell you whether the first test was accurate.

Frequently Asked Questions

Can I test my vehicle before my registration expires?

Yes, but only within 90 days of your expiration date. Testing earlier than that means your certificate will expire before your registration does, and you will have to test again. Check your registration card for the exact expiration date and count back 90 days to find the earliest testing date.

What if I fail the test and cannot afford the repair?

Colorado does not have a financial information program for emission repairs. However, some nonprofits and community action agencies offer low-cost repair services or can connect you with affordable mechanics. Contact your county's air pollution control division to ask about local resources.

Do I need an appointment or can I just walk in?

It depends on the station. Many private stations accept walk-ins, but some require appointments, especially during busy months. The Colorado Department of Revenue's station locator will tell you whether each station takes walk-ins. Calling ahead is always a safe option.

How long does it take to get my test results?

You get your results when ready after the test is complete. If you pass, the technician will give you a certificate on the spot that you can take to your registration renewal office. If you fail, you get a report showing which pollutants are out of range.

What if I move to a different county in Colorado?

Your emission test is valid statewide, so you can test in any county and use the certificate to renew your registration in any other county. You do not need a new test if you move within Colorado.