What Colorado emissions testing requires and who has to do it
Colorado requires emissions testing for most vehicles registered in the state, but the rules depend on where you live and how old your car is. If you live in the Denver metro area, the North Front Range (around Fort Collins), or the Pueblo area, you must test every two years. If you live elsewhere in Colorado, you do not need emissions testing at all — your vehicle only needs a safety inspection.
Your vehicle must pass an emissions test before you can renew your registration in a testing area. The test checks whether your car's exhaust meets state pollution standards. Diesel vehicles, motorcycles, and vehicles older than 1975 are exempt. Vehicles newer than the current model year minus 3 years are also exempt — so in 2024, a 2021 model would not need testing yet.
You can find out whether your address requires testing by entering your ZIP code on the Colorado Department of Public Health and Environment website. The site will tell you when ready whether you live in a testing area and when your vehicle's test is due.
Key Takeaways
- Emissions testing is required only in the Denver metro area, North Front Range, and Pueblo area — most of Colorado does not require it.
- You must test every two years before you can renew your vehicle registration in a testing area.
- Vehicles newer than three model years old, motorcycles, and diesel vehicles are exempt from testing.
- You can take your vehicle to any Colorado emissions testing station, not just one assigned to you.
- A test costs between $15 and $25 depending on the station, and you receive results when ready.
Where to find an emissions testing station in Colorado
Colorado does not assign you to a specific testing station. You can visit any station in the state that is licensed to perform emissions tests. The Colorado Department of Public Health and Environment maintains a searchable list of all active stations on its website, organized by county. You can search by your location or by the station name if you already know where you want to go.
Most testing stations are independent repair shops, not dealerships. Many are small garages that do general automotive work and offer emissions testing as one service. Some stations are busier than others — if you go during lunch hours or right after work, you may wait longer. Early morning or mid-afternoon on a weekday is usually faster.
You do not need an appointment at most stations. You can drive in, pay the fee, and have your vehicle tested the same day. A few stations do take appointments, which you can arrange by phone. Bring your vehicle registration and a valid ID.
What happens during the test and what causes a failure
The emissions test takes about 10 to 15 minutes. The technician will connect a probe to your vehicle's exhaust pipe and measure the levels of nitrogen oxides, carbon monoxide, and other pollutants. For vehicles with an onboard diagnostic system (most cars made after 1996), the technician will also read your vehicle's computer to check for any emissions-related trouble codes.
Your vehicle passes if the pollutant levels are below the state limits and your check engine light is not on. If your check engine light is on, the test will fail even if the pollutant levels are low. A vehicle also fails if the technician cannot read the onboard diagnostic system or if the system shows emissions-related codes.
Common reasons for failure include a faulty oxygen sensor, a loose or missing gas cap, a catalytic converter problem, or an engine that is running too rich (burning too much fuel). Many of these issues cause the check engine light to turn on. If your vehicle fails, the technician will give you a report showing which system failed. You can then take that report to a repair shop to have the problem fixed.
What to do if your vehicle fails the test
You have until your registration expires to get your vehicle repaired and retested. You do not have to return to the same station — you can go to any licensed station in Colorado. The retest fee is the same as the initial test, usually $15 to $25.
If you repair your vehicle and it still fails the retest, Colorado offers a waiver program for vehicles that have been repaired but cannot pass. To receive a waiver, you must spend at least $375 on repairs related to the emissions failure. You then take your repair receipts and your failed test report to the testing station, and the station will issue a waiver that allows you to renew your registration without passing the test.
The waiver is valid for one registration period (two years). After that, your vehicle must pass the test again. If you cannot afford the $375 in repairs, some nonprofits and community programs in Colorado offer low-cost repair information, though availability varies by county.
How to prepare your vehicle before testing
Before you go to a testing station, make sure your vehicle has been driven for at least 20 minutes so the engine is fully warmed up. A cold engine can produce higher emissions readings and cause a failure even if the vehicle would pass when warm. Drive on the highway if you can — a mix of highway and city driving warms the engine more thoroughly than city driving alone.
Check that your gas cap is tight and not cracked. A loose or damaged cap can trigger the check engine light and cause an automatic failure. If your check engine light is already on, have the code read before you go to the station. Many auto parts stores will read the code for free and tell you what system is affected.
If your vehicle is very old or has high mileage, consider having a pre-test inspection at a repair shop. A technician can check your oxygen sensors, catalytic converter, and fuel system before you pay for the official test. This costs extra but can save you money if a major repair is needed.
Understanding your test results and what the numbers mean
When you pass the test, you receive a printed report showing the pollutant levels your vehicle produced and the state limits for your vehicle's model year. The report also shows whether your onboard diagnostic system passed. You do not need to do anything with this report — the testing station sends the results electronically to the Colorado Department of Public Health and Environment, and your registration renewal is cleared.
If you fail, the report will show which pollutant exceeded the limit or which diagnostic code was found. The report uses technical abbreviations: NOx means nitrogen oxides, CO means carbon monoxide, and O2 means oxygen. If the report shows a code like P0420, that refers to a specific emissions system problem — you can search the code online or ask a repair shop what it means.
Keep your passing test report in your vehicle or with your registration documents. You do not need to show it to renew your registration, but it is useful proof if there is ever a question about whether your vehicle was tested.
Emissions testing important date and registration renewal
Your emissions test must be completed before your vehicle registration expires. The expiration date is printed on your registration card. You can test up to 60 days before your registration expires, so you do not have to wait until the last moment.
If your registration has already expired, you cannot legally drive your vehicle in Colorado. You must renew your registration before you can test. You can renew your registration online through the Colorado Department of Revenue website, by mail, or in person at a county clerk's office. Once your registration is renewed, you can then go for your emissions test if you live in a testing area.
If you move out of a testing area to a part of Colorado that does not require emissions testing, you no longer need to test. You only need a safety inspection. If you move into a testing area, you will need to test before your next registration renewal.
Frequently Asked Questions
Can I test my vehicle in a different county than where I live?
Yes. You can visit any licensed emissions testing station in Colorado, regardless of which county your vehicle is registered in. The test results are reported to the state, not to your county, so it does not matter where you test as long as you live in a testing area.
What if I just bought a used car and do not know when it was last tested?
Contact the Colorado Department of Public Health and Environment or check the online testing station locator — you can enter your vehicle's information and it will tell you when the last test was done and when the next one is due. You can also ask the seller for their test records.
Do I have to test if my vehicle has a temporary registration?
No. Temporary registrations are exempt from emissions testing. Once your permanent registration is issued, you must test before the first renewal if you live in a testing area.
What if my vehicle is registered out of state but I live in Colorado?
If you live in a Colorado testing area and your vehicle is registered in another state, you must still have an emissions test before you can register it in Colorado. You will need to register your vehicle in Colorado first, then test, then renew your registration.
How long does it take to get my test results?
You receive your results when ready when you finish testing. The technician prints a report on the spot. The results are also sent electronically to the state within 24 hours, so your registration renewal is cleared right away.