Colorado requires emissions testing in certain counties, and the rules depend on where you live and what you drive

Colorado's emissions program covers only specific counties in the Denver metro area and surrounding regions. If you live in Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, El Paso, Jefferson, Larimer, or Weld County, your vehicle must pass an emissions test before you can register it. If you live elsewhere in Colorado, you do not need an emissions test — your registration process stops at the standard vehicle inspection.

The test itself measures what comes out of your tailpipe: hydrocarbons, nitrogen oxides, carbon monoxide, and particulate matter. A vehicle passes if those levels stay below state limits. The test takes about 10 minutes and costs between $25 and $30, depending on the testing station. You can take the test at any Colorado Department of Revenue emissions testing station or at a private repair shop that holds an emissions testing license.

Timing matters. You must pass the test before you renew your registration, and you cannot renew online if you live in a testing county — you have to go in person or by mail and show proof of a passing test. If your vehicle fails, you have 60 days to fix it and retest at no additional charge.

Key Takeaways

  • Emissions testing is required only in Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, El Paso, Jefferson, Larimer, and Weld counties.
  • The test costs $25 to $30 and takes about 10 minutes at any state-licensed testing station or participating repair shop.
  • You must pass before you renew your registration, and you cannot complete registration online in a testing county without proof of a passing test.
  • If your vehicle fails, you have 60 days to repair it and retest for free at the same station.

Which counties require emissions testing

The Colorado Department of Public Health and Environment designates counties based on air quality. The current testing counties are Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, El Paso, Jefferson, Larimer, and Weld. These counties make up the Denver metro area and surrounding communities where air quality does not consistently meet federal standards.

If you live in a testing county, you must test every two years when you renew your registration — unless your vehicle is brand new (less than four model years old) or is a motorcycle. Diesel vehicles have separate testing standards and may be tested at fewer stations. Check the Colorado Department of Revenue website to confirm whether your specific vehicle type requires testing in your county.

Finding a testing station and scheduling

The Colorado Department of Revenue maintains a list of all licensed emissions testing stations on its website, organized by county. You can search by location and see which stations are open and what their hours are. Most stations are repair shops, quick-lube facilities, or dedicated testing centers in strip malls or commercial areas.

Walk-in testing is available at most stations, but wait times vary. During peak months (August through October, when many people renew registration), you may wait 30 minutes to an hour. Some stations accept online reservations through their own websites. Call ahead if you want to know current wait times or book a specific time slot.

What happens during the test

The technician will ask for your vehicle keys and your registration. They will drive your car onto a dynamometer — a machine with rollers that simulates driving — or perform a tailpipe test while the vehicle idles and revs. The machine measures emissions in real time and prints a result within minutes.

A pass means your vehicle meets Colorado standards and you can proceed with registration. A fail means one or more pollutants exceeded the limit. The technician will give you a printed report showing which emissions failed and by how much. You do not need to repair the vehicle at that station — you can take it anywhere for repairs.

Failing the test and what to do next

If your vehicle fails, you have 60 days from the test date to repair it and retest. The retest is free at the same station where you failed. You do not need to pay the $25 to $30 fee again. Keep your failing test report — you will need to show it when you return for the retest.

Common reasons for failure include a faulty oxygen sensor, a loose gas cap, a malfunctioning catalytic converter, or an engine that is running too rich (burning too much fuel). A repair shop can diagnose the problem by reading your vehicle's diagnostic trouble codes. If repairs cost more than you want to spend, some counties offer a Repair information Program that may help cover costs for low-income vehicle owners, though funding and may be able to access vary by county.

If you cannot repair the vehicle within 60 days, you can request a one-time extension from the Colorado Department of Revenue. Extensions are not automatic — you must request one before the 60-day window closes. After the extension expires, you cannot renew your registration until you pass a retest.

Vehicles exempt from testing

New vehicles (less than four model years old) are exempt from emissions testing for their first registration in Colorado. Once they reach four model years old, they must test like any other vehicle. Motorcycles, mopeds, and vehicles registered as antiques or collectibles are also exempt.

Diesel vehicles are tested, but at fewer stations and with different standards. Electric vehicles do not require emissions testing. If you are unsure whether your vehicle is exempt, check the Colorado Department of Revenue website or call the testing station before you go.

Registration and proof of testing

Once you pass the test, the testing station sends your result electronically to the Colorado Department of Revenue. You do not need to print or carry the test report, though keeping a copy for your records is a good idea. When you renew your registration in person or by mail, the state will have your passing test on file.

If you renew by mail, include a copy of your passing test report with your registration renewal form. If you renew in person at a county clerk's office, bring your test report or your vehicle registration card showing the test date. Online renewal is not available in testing counties unless your vehicle is exempt.

Frequently Asked Questions

What if I move out of a testing county after I fail?

You still have 60 days from the original test date to retest and pass, even if you move. The 60-day clock does not reset based on your move. Contact the original testing station or the Colorado Department of Revenue to arrange a retest in your new county if needed.

Can I test my vehicle early, before my registration expires?

Yes. You can test up to 120 days before your registration expires. The test result is valid for two years from the test date, so testing early gives you flexibility if repairs are needed. This can be useful if you know your vehicle is aging and may have trouble passing.

What if the testing machine breaks down during my test?

If the equipment malfunctions during your test, the station will reschedule you at no charge. You are not charged for a failed test caused by equipment failure. Ask the technician to document the malfunction on your paperwork so there is no confusion later.

Do I need emissions testing if I only drive my vehicle part of the year?

Yes, if you register the vehicle in Colorado and live in a testing county, you must test before renewal regardless of how often you drive it. Seasonal or part-time registration does not exempt you from the testing requirement.

What happens if I register my vehicle without a passing test?

The Colorado Department of Revenue will not issue a registration sticker in a testing county without proof of a passing emissions test. Your registration will be incomplete, and driving without valid registration is a violation. If you miss the important date, you must test and pass before you can complete registration.