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

Colorado's emissions program tests whether your vehicle's exhaust meets state air quality standards. The program is mandatory in the Denver metro area and several other regions, but not statewide. If you live in one of the designated air quality areas—primarily the Front Range from Fort Collins south through Colorado Springs—your vehicle must pass an emissions test before you can renew your registration. Vehicles in rural areas outside these zones are not required to test.

The test itself is straightforward: a technician plugs a diagnostic scanner into your vehicle's onboard computer port and reads emissions data. For most cars, the test takes 10 to 15 minutes and costs between $20 and $30. You do not need to do anything special to prepare beyond making sure your check engine light is off and your vehicle runs normally.

Colorado's program is run by the Colorado Department of Public Health and Environment (CDPHE), which sets the standards and oversees testing stations. Individual counties within the designated areas manage their own testing programs, so rules and testing locations vary slightly by county.

Key Takeaways

  • Emissions testing is required only in designated air quality areas, primarily the Denver metro region and northern Front Range, not across all of Colorado.
  • Your vehicle must pass the test before you can renew your registration, and you typically have until your registration expires to complete it.
  • The test reads data from your vehicle's onboard computer and takes about 15 minutes; a passing test costs $20 to $30.
  • If your vehicle fails, you have options to repair and retest, and some vehicles may be exempt based on age or type.
  • You can find testing stations through your county's air quality program or the CDPHE website.

Which Colorado counties and regions require emissions testing

The Denver metro nonattainment area is the core region where testing is mandatory. This includes Denver, Boulder, Broomfield, Adams, Arapahoe, Douglas, Jefferson, and Weld counties. The Colorado Springs area (El Paso County) also requires testing. Fort Collins and Larimer County have their own emissions program with slightly different rules.

If you live outside these designated areas—in rural Colorado, the Western Slope, or the San Luis Valley—your vehicle is not subject to emissions testing. However, if you move into a designated area or register a vehicle there, you must comply with that area's program.

You can confirm whether your address falls in a testing area by entering your zip code on the CDPHE Air Quality Control Commission website or by calling your county's air quality program directly. County health departments maintain lists of approved testing stations and current program rules.

How the emissions test works and what happens if you fail

The test is called an On-Board Diagnostic (OBD) test. The technician connects a scanner to the diagnostic port under your steering wheel, which reads data from your vehicle's emissions control system. The scanner checks whether your vehicle's computer has detected any emissions-related problems and whether your catalytic converter and other emissions equipment are functioning.

If your vehicle passes, you receive a passing certificate and can renew your registration. If it fails, the technician will provide a report showing which emissions systems are not working correctly. You then have options: repair the vehicle and retest, seek a waiver if repairs are too expensive, or in some cases request an extension.

Retesting costs the same as the initial test. Many testing stations can retest you the same day if you have repairs done quickly, though you may need to schedule an appointment. If you fail a second time, you can continue to retest, but your registration cannot be renewed until you pass.

Vehicles that may be exempt from Colorado emissions testing

Vehicles older than a certain year may be exempt depending on your county. In the Denver area, vehicles model year 1981 and older are typically exempt. Some counties exempt vehicles 25 years or older. Motorcycles, diesel vehicles over 14,000 pounds, and some specialty vehicles may also be exempt or tested under different standards.

New vehicles—usually those model year 2010 and newer—often pass automatically because their emissions systems are newer and the test is designed to catch older, failing equipment. However, a new vehicle with a check engine light or a malfunctioning emissions system can still fail.

To find out whether your specific vehicle is exempt, contact your county's air quality program or ask the testing station when you arrive. Bring your vehicle registration and title so the technician can verify the model year and vehicle type.

What to do if your vehicle fails the emissions test

First, get a copy of the failure report from the testing station. This report tells you which emissions system is not working—usually the catalytic converter, oxygen sensors, or the vehicle's computer itself. Take this report to a repair shop and have a mechanic diagnose the problem.

Some repairs are inexpensive (replacing an oxygen sensor might cost $100 to $300), while others are costly (a catalytic converter replacement can run $500 to $2,000 or more). If repair costs are very high, you may be able to request a hardship waiver from your county. Waivers allow you to renew your registration without passing the test if you can show that repairs would cost more than a certain percentage of your vehicle's value—usually 7 to 10 percent, depending on the county.

To request a waiver, contact your county's air quality program and ask for their hardship waiver form. You will need to provide the failure report, repair estimates, and proof of your vehicle's value. The county will review your request and notify you whether the waiver is granted. Even with a waiver, you must still attempt repairs or document that you tried to find a repair shop.

Finding a testing station and scheduling your test

Your county's air quality program maintains a list of approved testing stations. You can find this list on the county health department website or by calling the air quality office directly. Testing stations include independent repair shops, dealerships, and dedicated emissions testing centers.

You do not need an appointment at many stations, but calling ahead is a good idea, especially during busy seasons (late summer and fall, when many people renew registrations). Bring your vehicle registration and a valid ID. The technician will verify that the vehicle matches your registration and then run the test.

Testing stations are open during regular business hours, typically 8 a.m. to 5 p.m. on weekdays. Some counties offer evening or weekend testing at certain locations. If you fail and need to retest, you can often return to the same station within a few days.

Timing: when you need to test and how long it takes

You must pass the emissions test before your vehicle registration expires. Most people test within the two months before their registration renewal date. You can test earlier if you want—there is no penalty for passing early—but you cannot renew your registration until you have a passing test certificate.

The test itself takes 10 to 15 minutes. Getting the results takes a few minutes more. If you fail and need repairs, the time depends on your repair shop's schedule and the complexity of the repair. straightforward repairs might be done the same day; more involved work could take several days.

If you are close to your registration expiration date and your vehicle fails, contact your county air quality program when ready. Some counties can grant short extensions if you have already scheduled repairs or are waiting for parts. Do not wait until your registration expires—driving with an expired registration is illegal, even if you are in the process of getting repairs done.

Frequently Asked Questions

Do I have to test my vehicle every year?

Yes, in designated areas, you must pass an emissions test before renewing your registration each year. The test is tied to your registration renewal, so you cannot renew without a passing certificate. Some counties allow you to test up to 60 days before your registration expires.

What if my check engine light is on?

Your vehicle will likely fail the test if the check engine light is on, because the light indicates that your vehicle's computer has detected an emissions-related problem. Have the vehicle scanned at a repair shop to find out what the problem is, get it fixed, and then retest. The light must be off before you test.

Can I test in a different county than where I live?

Yes, you can test at any approved station in any county within the designated testing area. However, you must still follow the rules of the county where your vehicle is registered. If you move to a new county, you may need to follow that county's specific testing rules and important date.

What happens if I drive with an expired registration because I failed the emissions test?

Driving with an expired registration is illegal and can result in a traffic citation and fine, even if you are actively trying to repair your vehicle and retest. If you are close to your expiration date and your vehicle fails, contact your county when ready to ask about a short extension or expedited retesting.

Are electric vehicles required to test?

No, fully electric vehicles are exempt from emissions testing in Colorado because they produce no tailpipe emissions. Plug-in hybrid vehicles may be subject to testing depending on the county and how the vehicle is classified. Check with your county's air quality program if you are unsure about your specific vehicle type.