What Colorado's emissions test measures and who has to take 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. In the Denver metro area and a few other urban counties, all vehicles model year 1981 and newer need to pass an emissions test every two years. In rural Colorado counties, the requirement is less strict — vehicles model year 1982 and newer need testing, but only every three years, and some rural counties have no emissions testing requirement at all.

The test itself measures what comes out of your tailpipe: nitrogen oxides, particulate matter, and hydrocarbons. A machine reads your vehicle's onboard diagnostic system and runs a short drive cycle to see whether your emissions fall within Colorado's limits. The test takes about 30 minutes total, though the actual driving portion lasts only a few minutes.

Diesel vehicles, motorcycles, and vehicles over 14,000 pounds have different rules or are exempt entirely. If you are unsure whether your vehicle needs testing, the Colorado Department of Public Health and Environment website has a county-by-county breakdown, or you can ask at any testing station.

Key Takeaways

  • Denver metro and surrounding counties require emissions testing every two years for vehicles model year 1981 and newer; rural counties have different schedules or no requirement.
  • The test measures tailpipe emissions through a short drive cycle and takes about 30 minutes at a licensed testing station.
  • You can find your vehicle's test due date and locate nearby stations through the Colorado Department of Public Health and Environment website or by calling 303-692-3000.
  • A failed test costs nothing to retake, but you cannot register your vehicle until it passes.
  • Common reasons for failure include a faulty oxygen sensor, a loose gas cap, or an engine light that is on.

Where to get your emissions test done in Colorado

Colorado has two types of emissions testing stations: state-certified private stations and the state's own testing centers. Private stations are faster and more convenient — there are hundreds across the state, and you can usually get in and out in under an hour. You can find a private station near you by entering your zip code on the Colorado Department of Public Health and Environment website or by searching "emissions testing near me" online.

State testing centers exist in Denver, Colorado Springs, and Fort Collins. These are slower and more crowded than private stations, but they cost less — usually around $20 to $25, compared to $30 to $50 at private stations. If you are on a tight budget or your vehicle has failed before, a state center may be worth the wait.

When you arrive at any station, bring your vehicle registration and proof of insurance. The technician will plug a diagnostic scanner into your vehicle's onboard system and run the test. You will get your results on the spot, either a pass or a fail with a printout showing which emissions exceeded the limit.

What happens if your vehicle fails the emissions test

A failed test does not cost you anything to retake, and you can go back to any station when ready. However, you cannot register or renew your registration until you pass. If your registration expires before you pass, you are driving illegally, so it is worth fixing the problem quickly.

The most common reasons for failure are a faulty oxygen sensor, a loose or missing gas cap, a clogged air filter, or an engine check light that is on. Many of these are cheap fixes — a gas cap costs a few dollars, and an air filter costs $15 to $30. Before you spend money at a mechanic, check these things yourself or ask the testing station what the specific failure was.

If the failure is something more serious — a catalytic converter problem, a fuel injector issue, or transmission trouble — you may need a mechanic. Colorado law says you have up to 60 days after a failed test to fix the problem and retest. If you cannot afford the repair, some nonprofits and county programs offer emissions repair information, though funding and availability vary by county.

How to prepare your vehicle before testing

The best preparation is to keep up with basic maintenance: change your oil on schedule, replace your air filter every 12,000 to 15,000 miles, and fix any check engine light as soon as it appears. If your vehicle is due for testing and you have not done this, do it before you go.

Right before your test, check your gas cap — make sure it is tight and not cracked. A loose cap is one of the easiest reasons to fail, and it takes 10 seconds to fix. If your check engine light is on, take your vehicle to a mechanic or an auto parts store that reads diagnostic codes for free. Knowing what the code is before you test can save you a failed test and a second trip.

Do not use fuel additives or "emissions cleaner" products in the days before your test — they do not help and can sometimes cause problems. Just drive normally and let the vehicle warm up fully before you arrive at the testing station.

Understanding your emissions test results

If you pass, you will get a certificate or sticker that you can use to renew your registration. Keep this paperwork — you will need to show it when you register your vehicle with the Colorado Department of Motor Vehicles. A passing test is valid for two years in metro Denver or three years in rural counties, depending on where you live.

If you fail, the printout will show which emissions exceeded the limit. It will list nitrogen oxides (NOx), hydrocarbons (HC), carbon monoxide (CO), or particulate matter (PM), along with the limit and what your vehicle produced. This information tells a mechanic what system to focus on — for example, high NOx usually points to the oxygen sensor or fuel injector, while high CO usually means a rich fuel mixture.

You do not have to take the printout to a mechanic, but it helps them diagnose the problem faster. Some testing stations will recommend a mechanic, but you are free to choose your own. If you want a second opinion on whether the test was accurate, you can request a retest at a different station — the results should be similar if your vehicle truly has an emissions problem.

Emissions testing requirements by Colorado county

Colorado divides emissions testing into three categories based on air quality and population. The Denver metro area — including Denver, Adams, Arapahoe, Boulder, Douglas, El Paso, Jefferson, Larimer, and Weld counties — requires testing every two years for vehicles model year 1981 and newer. This is the strictest standard because these counties have historically had air quality challenges.

A second group of counties, including Pueblo and some others, requires testing every three years for vehicles model year 1982 and newer. The remaining rural counties have no emissions testing requirement at all, though vehicles registered there can still be tested if the owner wants to.

If you move between counties or are unsure which rule applies to you, check the Colorado Department of Public Health and Environment website or call 303-692-3000. The state can tell you your vehicle's test due date and which county rules explore to your address.

What to do if you cannot pass the emissions test

If your vehicle repeatedly fails or the repair cost is very high, you have a few options. First, check whether your vehicle qualifies for the Repair information Program or the Scrappage Program, both run by the Colorado Department of Public Health and Environment. These programs help low-income vehicle owners pay for repairs or replace very old vehicles that cannot pass. Funding and income limits vary by year and county, so call 303-692-3000 to ask whether your situation qualifies.

Second, if the repair is genuinely unaffordable and your vehicle is very old, you may be able to get a temporary waiver or exemption. These are rare and require documentation of the repair cost and your income, but they exist. Contact your county's air quality program directly to ask about this option.

Third, if you are in a rural county with no testing requirement, you can register your vehicle there instead. This is legal if you actually live in that county, but registering in a county where you do not live to avoid emissions testing is fraud and can result in fines and registration suspension.

Frequently Asked Questions

How do I find out when my vehicle's emissions test is due?

Go to the Colorado Department of Public Health and Environment website and enter your vehicle identification number (VIN) and license plate number. The system will show your test due date and whether you are in a two-year or three-year testing cycle. You can also call 303-692-3000 and a staff member will look it up for you.

Can I test my vehicle early, before the due date?

Yes. You can test early at any licensed station, and if you pass, that new test date becomes your next due date. This is useful if you are planning to sell your vehicle or if you want to get testing done before a busy season.

What if I just bought a used vehicle in Colorado — when does it need testing?

The test due date follows the vehicle, not the owner. When you register it in your name, the Colorado Department of Motor Vehicles will tell you when the next test is due based on the vehicle's history. If the previous owner just passed, you may not need to test for two or three years.

Do I have to test at a state center, or can I use a private station?

You can use either. Private stations are faster and more convenient; state centers are cheaper. Both are equally valid, and the results are the same. Choose whichever works best for your schedule and budget.

What if I move out of Colorado — do I still need to pass the emissions test?

No. Once you register your vehicle in another state, Colorado's emissions requirement no longer applies. However, your new state may have its own emissions testing rules, so check with your new state's motor vehicle department.