Colorado requires emission testing for most vehicles, and the rules depend on where you live and what you drive

Colorado's emission testing program, run by the Colorado Department of Public Health and Environment (CDPHE), is mandatory in certain areas of the state. The Denver Metro area — which includes Denver, Boulder, Fort Collins, and surrounding counties — has the strictest requirements because air quality in the Front Range is monitored closely. If you live in this region, you must pass an emission test every two years as part of your vehicle registration renewal. Outside the Denver Metro area, Colorado does not require emission testing at all.

The test itself checks whether your vehicle's exhaust meets state standards for nitrogen oxides, particulate matter, and other pollutants. Diesel vehicles, gasoline vehicles, and hybrids all test differently. The test takes about 10 minutes and costs between $20 and $30, depending on the testing station. You cannot register your vehicle without a passing test result if you live in a required area.

Key Takeaways

  • Emission testing is required only in the Denver Metro area and a few surrounding counties; most of Colorado has no testing requirement.
  • Tests must be completed every two years during your vehicle registration renewal cycle, and you cannot renew registration without a passing result.
  • Vehicles older than model year 1981 and some electric vehicles are exempt from testing, but most gasoline and diesel vehicles must test.
  • If your vehicle fails, you have 60 days to repair it and retest at no additional charge, and some repairs may may have access to for state rebate programs.
  • You can find approved testing stations through the CDPHE website or by searching for "emission testing near me" in the Denver Metro area.

Which Colorado counties require emission testing

The Denver Metro area includes Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, Jefferson, and Weld counties. These eight counties are designated as a nonattainment area by the U.S. Environmental Protection Agency (EPA) because ozone levels exceed federal standards during summer months. If your vehicle is registered in any of these counties, you must test.

El Paso County (Colorado Springs) has a separate, less stringent program called the El Paso County Air Quality Program. Vehicles registered there must test every two years, but the standards are different from the Denver Metro area. If you live anywhere else in Colorado — including Larimer, Pueblo, Mesa, or any rural county — emission testing is not required.

You can check which county your vehicle is registered in by looking at your registration card or contacting your county clerk's office. If you move to a different county, your testing requirement may change, so verify the rules for your new address before your next registration renewal.

What vehicles are exempt from testing

Vehicles manufactured before 1981 are exempt from emission testing in Colorado, regardless of where they are registered. This exemption applies to classic cars, antiques, and older trucks. Motorcycles are also exempt. Electric vehicles (EVs) do not test because they produce no tailpipe emissions.

Hybrid vehicles must test, even though they run on both electric and gasoline power. The test measures what comes out of the tailpipe when the engine is running, so hybrids are treated the same as gasoline vehicles. Diesel vehicles must test as well, using a different protocol that measures particulate matter and opacity.

Vehicles with a gross vehicle weight rating (GVWR) over 14,000 pounds — typically large trucks and commercial vehicles — are exempt. If you are unsure whether your vehicle qualifies for an exemption, the testing station can tell you when you arrive, or you can call the CDPHE Air Pollution Control Division at 303-692-3100.

How to schedule and pass your emission test

You can find approved testing stations through the CDPHE website at cdphe.colorado.gov or by searching online for "emission testing" in your county. Most stations are independent repair shops, tire shops, or dedicated testing facilities. Call ahead to confirm hours and whether you need an appointment; some stations accept walk-ins, while others book by appointment only.

Bring your vehicle registration card and a valid photo ID. The technician will plug a diagnostic scanner into your vehicle's onboard diagnostic port (OBD-II), which is usually located under the steering wheel or dashboard. The test runs the vehicle through a standardized cycle and measures emissions. The whole process takes about 10 minutes. You will receive a pass or fail result when ready.

To pass, your vehicle must meet Colorado's emission standards for its model year and fuel type. Vehicles in good mechanical condition with no check engine light and regular maintenance almost always pass. If your check engine light is on, the vehicle will fail automatically, even if emissions are within limits. Have the light diagnosed and repaired before testing.

What happens if your vehicle fails the emission test

If your vehicle fails, you have 60 days from the test date to repair the problem and retest at no additional charge. The test report will tell you which emission system failed — for example, the oxygen sensor, catalytic converter, or fuel system. Take this report to a repair shop and have the technician diagnose and fix the problem.

Common failures include a faulty oxygen sensor, a clogged catalytic converter, a loose or missing gas cap, or a malfunctioning fuel injector. These repairs typically cost between $100 and $800, depending on the part. Some repairs, such as replacing a catalytic converter, may may have access to for the Colorado Vehicle Emissions Repair information Program, which can help cover costs for low-income vehicle owners. Contact the CDPHE to learn whether you meet income requirements.

After the repair, return to any approved testing station and retest. If you pass, you can complete your registration renewal. If you fail again, you have another 60 days to repair and retest. If you cannot repair the vehicle within 60 days, you cannot register it in Colorado until it passes.

Timing your emission test with vehicle registration renewal

Your emission test must be completed before you renew your vehicle registration. Colorado sends registration renewal notices about 45 days before your registration expires. The notice will tell you whether your vehicle requires an emission test.

You can test anytime during the 60 days before your registration expires. Testing earlier gives you time to repair and retest if you fail. If you test in the month before expiration and fail, you may not have enough time to repair and retest before the important date. Plan to test at least two months before your registration expires to avoid this problem.

You can renew your registration online, by mail, or in person at your county clerk's office, but only after you have a passing emission test result. The test result is valid for 60 days, so if you test early and then wait to renew, make sure the result has not expired.

Emission testing costs and where to find testing stations

The cost of an emission test in Colorado ranges from $20 to $30, depending on the testing station and vehicle type. Diesel vehicles may cost slightly more than gasoline vehicles at some stations. This is a one-time fee per test; if you fail and retest within 60 days, the retest is free.

To find a testing station near you, visit the CDPHE website and use their approved testing station locator, or search online for "emission testing" plus your city or county name. Most stations are open during standard business hours, Monday through Friday, and some offer Saturday hours. Call ahead to confirm hours and whether you need an appointment.

Independent repair shops, tire shops, and dedicated emission testing facilities all perform the test using the same equipment and standards. There is no difference in test quality between station types, so choose based on location and convenience. If a station seems unusually cheap or unusually expensive, call another station to compare.

Frequently Asked Questions

Can I test my vehicle before my registration expires?

Yes. You can test anytime, but the result is valid for 60 days. If you test more than 60 days before your registration expires, the result will expire before you can use it for renewal. Test within 60 days of your registration expiration date to may support the result is still valid when you renew.

What if I move out of the Denver Metro area after I test?

If you move to a county that does not require testing, you do not need to retest before registering your vehicle in the new county. If you move to a county that does require testing, you will need to test before your next registration renewal in that county. Contact your new county clerk's office to confirm the requirement.

Do I have to test if my vehicle has a check engine light on?

You can test with the light on, but your vehicle will fail automatically. Have the problem diagnosed and repaired first, then clear the light and retest. A repair shop can diagnose the problem and clear the light after the repair is complete.

What if my vehicle is registered in a county that does not require testing but I drive it in Denver?

Your vehicle must meet the emission standards of the county where it is registered, not where you drive it. If your vehicle is registered outside the Denver Metro area, you do not need to test, even if you drive in Denver frequently. However, if you move your registration to a Denver Metro county, you will need to test before your next renewal.

Can I test my vehicle early to get ahead of the important date?

Yes, but remember that the test result is valid for only 60 days. If you test more than 60 days before your registration expires, you will need to test again before renewal. The best time to test is within 60 days of your registration expiration date.