What Colorado's emissions test checks and who has to take it

Colorado requires an emissions test for most vehicles registered in certain counties, but not all of the state. The test measures what comes out of your tailpipe — specifically nitrogen oxides, particulate matter, and hydrocarbons — to make sure your vehicle meets state air quality standards. A mechanic or technician runs the test at a licensed emissions testing station, and it takes about 10 to 15 minutes.

You need an emissions test if you live in one of Colorado's designated air quality areas. These are mostly the Denver metro area, parts of the Front Range, and a few other regions where air pollution has historically been a concern. If you live in a rural county or a place where the air quality is consistently good, you may not need one. The Colorado Department of Public Health and Environment maintains the current list of counties and areas that require testing.

Even if your county requires testing, you do not need one every year. Most vehicles need a test every two years, though some newer cars (usually 2 to 4 years old, depending on the model year) may be exempt. Vehicles older than a certain age — typically 25 years or more — are also often exempt. Your vehicle registration paperwork or the Colorado DMV website will tell you whether your specific vehicle needs a test and when.

Key Takeaways

  • Emissions testing is required in Colorado's air quality areas (mainly Denver metro and the Front Range) but not statewide, and you can learn about your address requires it on the Colorado DMV website.
  • The test measures tailpipe emissions and takes 10 to 15 minutes at a licensed testing station, which you can find through the state's online station locator.
  • Most vehicles need a test every two years, but newer cars and vehicles older than 25 years are often exempt — check your registration notice to confirm your vehicle's requirement.
  • If your vehicle fails, you have 60 days to repair it and retest at no additional cost, and some repairs may be covered by Colorado's vehicle repair information program if your household income is below a certain threshold.
  • You cannot renew your vehicle registration without a passing emissions test result if your vehicle is required to have one.

How to find a testing station and schedule an appointment

Colorado's Department of Public Health and Environment runs an online station locator at cdphe.colorado.gov where you can enter your zip code and see all licensed emissions testing stations near you. Most stations are independent repair shops, some are dealerships, and a few are dedicated emissions-only facilities. The locator shows their hours, phone numbers, and sometimes whether they accept walk-ins or require appointments.

Many stations do accept walk-ins, especially smaller ones, but calling ahead is safer — it saves you a trip if they are busy or closed. The test costs money (the fee varies by station, typically between $25 and $35), and you will need to bring your vehicle registration or proof of ownership. Some stations may ask for your driver's license as well.

You can test your vehicle anytime during the two-year window your registration notice specifies. There is no penalty for testing early, so if you know you will be busy later in the cycle, you can get it done whenever it is convenient. The test result is sent electronically to the Colorado DMV, so you do not need to bring a paper copy to the registration office.

What happens if your vehicle fails the emissions test

If your vehicle does not pass, the testing station will give you a detailed report showing which emissions were too high. This report is important — it tells a mechanic what to look for when they diagnose the problem. Common reasons for failure include a faulty oxygen sensor, a loose gas cap, a malfunctioning catalytic converter, or issues with the engine control system.

You have 60 days from the test date to repair your vehicle and retest at no additional charge. The retest is free at the same station or any other licensed station. If you pass the retest within that 60-day window, your registration can proceed normally. If you do not retest within 60 days, you will need to pay for a new test and start the clock over.

If the repair is expensive, Colorado offers a vehicle repair information program for households below a certain income level. The program can cover part of the cost of emissions-related repairs. You can find out whether you may have access to by contacting your local air quality office or asking the testing station — they often have information about the program on hand.

Repairs and what to expect at a mechanic

Once you have the emissions test report, take it to a mechanic you trust. The report tells them exactly what failed, which narrows down what they need to check. Some repairs are straightforward and cheap — replacing a gas cap or clearing a fault code — while others, like catalytic converter replacement, can be several hundred dollars.

Before authorizing any major repair, ask the mechanic for a written estimate and ask whether the repair is may provide to fix the emissions problem. Some shops will warranty the repair for a certain period, meaning if you fail again shortly after, they will redo the work at no cost. This is worth asking about, especially if the repair is expensive.

After the repair is done, the mechanic may clear the vehicle's fault codes and drive it to make sure the check engine light does not come back on. This is normal. You can then take the vehicle back to any emissions testing station for the retest. Bring your repair receipt — some stations like to see it, though it is not always required.

Renewing your registration with a passing emissions result

Once your vehicle passes the emissions test, the result is automatically sent to the Colorado DMV. You can renew your registration online at colorado.gov/dmv, by mail, or in person at a DMV office. The system will show whether a passing emissions test is on file for your vehicle.

If your vehicle is required to have an emissions test and you try to renew without one, the DMV will not process your registration. You will get a notice telling you to complete the test first. This is why it is important to know whether your vehicle needs one — if you skip it by mistake, you cannot legally drive until you test and pass.

Your registration renewal notice will arrive in the mail about 30 to 45 days before your current registration expires. It will clearly state whether an emissions test is required for your vehicle. If it says yes, you have until the expiration date to get the test done and pass it before renewing.

Vehicles that are exempt from emissions testing

Colorado exempts certain vehicles from emissions testing based on age and type. Vehicles that are 25 years old or older are generally exempt, as are some electric vehicles and plug-in hybrids. Very new vehicles (usually those that are 2 to 4 years old, depending on the model year) are also exempt for their first few years.

Motorcycles, mopeds, and some other specialty vehicles have different rules. Diesel vehicles have their own emissions standards and testing procedures. If you are unsure whether your vehicle is exempt, check your registration renewal notice — it will say "emissions test required" or "emissions test not required" clearly at the top.

If you believe your vehicle should be exempt but your notice says it needs a test, you can contact the Colorado DMV or your local air quality office to ask about it. Bring your vehicle identification number (VIN) and registration paperwork.

What to do if you move or buy a used vehicle in Colorado

If you move into a county that requires emissions testing, your vehicle will need a test before you can renew your registration in that county. The test requirement is based on where you register the vehicle, not where you lived before. When you update your address with the DMV, your next registration renewal notice will reflect the new requirement.

If you buy a used vehicle in Colorado, the previous owner's emissions test does not transfer to you. You will need your own test before you can register it in your name. The timing depends on when the previous owner last tested — if they tested recently and you are buying the vehicle early in the two-year cycle, you may have a while before you need to test. If they tested near the end of the cycle, you may need to test soon after purchase.

When you buy a used vehicle, ask the seller when the last emissions test was done. This information is on the registration paperwork. Knowing this helps you plan when you will need to test after you take ownership.

Frequently Asked Questions

Do I have to test my vehicle if I just moved to Colorado?

Only if you register it in a county that requires emissions testing. When you register your vehicle with the Colorado DMV, they will tell you whether a test is needed based on your address. If your county requires it, you will need a passing test before your registration is active.

What if I fail the emissions test twice?

You have 60 days from each test date to repair and retest. If you fail a second time, you still have 60 days from that second test to repair and retest again. There is no limit to how many times you can retest within the 60-day window, as long as you keep retesting before the important date.

Can I test my vehicle before my registration expires?

Yes. You can test anytime during your two-year cycle. Testing early does not hurt — the result is valid for two years from the test date. This is useful if you know you will be busy later or want to get it done early.

What if the testing station says my vehicle cannot be tested?

Some vehicles have mechanical problems that prevent the test from running — for example, a check engine light that will not clear, or a transmission that will not shift properly. Ask the station what the problem is. You may need to have a mechanic look at it first before the test can be completed.

How do I know if my vehicle is registered in an emissions testing area?

Your registration renewal notice will say whether an emissions test is required. You can also check the Colorado DMV website or call your local air quality office with your zip code. The state's emissions station locator also shows which areas require testing.