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 not all counties enforce the same rules. The test measures how much pollution your vehicle's exhaust produces — specifically nitrogen oxides, particulate matter, and hydrocarbons. A machine reads your vehicle's onboard diagnostic system and runs a tailpipe test to see whether your emissions fall within state limits.
You need an emissions test if you register a vehicle in one of Colorado's eight ozone nonattainment areas: the Denver metro area (Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, El Paso, Jefferson, Larimer, Weld, and Weld County portions), parts of the Front Range, and a small area around Pueblo. If you live outside these counties, you do not need an emissions test — your registration renewal is simpler.
The test applies to most gasoline and diesel vehicles model year 1975 and newer. Motorcycles, RVs, and vehicles registered as antiques or collector vehicles are exempt. Electric vehicles do not need emissions testing.
Key Takeaways
- Colorado's emissions test is required only in eight counties in the Denver metro area, parts of the Front Range, and around Pueblo — not statewide.
- The test costs between $20 and $30 and takes about 10 minutes at a certified testing station.
- Your vehicle must pass before you can renew your registration, and you have until your registration expires to complete the test.
- If your vehicle fails, you have 60 days to repair it and retest at no additional charge at the same station.
- You can find testing stations and schedule appointments through the Colorado Department of Public Health and Environment website.
Where to find a testing station and how to schedule
The Colorado Department of Public Health and Environment maintains a searchable list of certified emissions testing stations on its website. You can filter by county and city to find stations near you. Most stations are independent repair shops, not dealerships, and many accept walk-ins, though scheduling an appointment usually means shorter wait times.
Call ahead to confirm hours and whether the station is currently accepting tests. Some stations close seasonally or have limited availability during peak testing periods (typically before registration important date). A few stations operate mobile units that travel to different locations — the CDPHE website lists their schedules.
Bring your vehicle registration and a valid ID. The test takes about 10 minutes. You do not need to bring any paperwork about your vehicle's maintenance or repair history unless it has previously failed.
What happens during the test and what results mean
The technician will connect a diagnostic scanner to your vehicle's onboard diagnostic port (usually located under the steering wheel). The scanner reads your vehicle's emissions control system data. The technician will then run a tailpipe test, inserting a probe into your exhaust to measure what comes out.
A pass means your emissions are within Colorado's limits. You will receive a printed pass certificate or a digital record that the testing station sends to the Colorado Division of Motor Vehicles. You can then renew your registration online, by mail, or in person.
A fail means your vehicle's emissions exceed state limits. The technician will provide a report showing which emissions were too high. You have 60 days from the test date to repair your vehicle and retest at the same station at no additional charge. If you retest at a different station, you will pay the testing fee again.
Some vehicles receive a conditional pass if the diagnostic system detects a problem but the vehicle still meets emissions limits. You will need to repair the issue before your next test, but you can renew your registration now.
Common reasons vehicles fail and what repairs typically cost
The most common failure causes are a faulty oxygen sensor, a loose or missing gas cap, a malfunctioning catalytic converter, or an engine misfire. Many of these repairs are straightforward and inexpensive — a gas cap costs $10 to $30, and an oxygen sensor replacement typically runs $150 to $300 at an independent shop.
Catalytic converter problems are more costly, ranging from $400 to $1,200 or more depending on your vehicle. However, if your vehicle is still under the manufacturer's emissions warranty (usually eight years or 80,000 miles), the repair may be covered by the manufacturer at no cost to you.
Before paying for repairs, ask the testing station for the specific diagnostic code from your vehicle's computer. Take that code to a trusted mechanic — it will help them diagnose the problem faster and more accurately than guessing. Some repair shops offer free or low-cost diagnostic scans.
Timing: when you need to test and what happens if you miss the important date
You must pass an emissions test before your vehicle registration expires. The test is valid for two years from the date you take it. If your registration expires on June 30, you can test anytime up to and including June 30.
If your registration has already expired and you have not passed an emissions test, you cannot legally drive the vehicle. You will need to test, pass, and then renew your registration before the vehicle is legal again. Driving an unregistered vehicle can result in a traffic citation.
If you are renewing your registration early (more than 60 days before expiration), you can test up to 60 days before your renewal date. Testing earlier than that will not count toward your current renewal.
What to do if your vehicle fails and you cannot afford repairs
Colorado offers a Repair information Program for low-income vehicle owners whose vehicles fail emissions testing. The program provides grants of up to $500 toward repairs at participating repair shops. You must meet income requirements (based on federal poverty guidelines) and own a vehicle model year 1996 or newer.
Contact your county's air quality division or the Colorado Department of Public Health and Environment to learn whether your county participates and how the process works. Some counties have additional local programs. The process process typically requires proof of income and the emissions test failure report.
If repairs cost more than the grant covers, ask the repair shop whether they offer payment plans or whether they participate in any manufacturer warranty programs. Some shops will also negotiate lower labor costs for low-income customers.
Emissions testing for vehicles with recent repairs or modifications
If you have recently had emissions-related repairs done, the vehicle's diagnostic system may need time to relearn normal operating patterns before testing. Most vehicles need 50 to 100 miles of normal driving after a repair before the system is ready. If you test too soon after a repair, you may receive a false fail.
If your vehicle has been modified — such as a custom exhaust system or engine tuning — it may not pass Colorado's emissions test even if it passes in other states. Colorado requires that all emissions control equipment remain in place and functional. Modifications that disable or remove emissions equipment will cause a fail.
If you have made modifications and are concerned about passing, contact a testing station before scheduling your test. Some technicians can advise whether your specific modifications will affect the results.
Frequently Asked Questions
Can I test in a different county than where I live?
Yes. You can test at any certified station in Colorado, even if it is outside your home county. However, you must test in one of the eight nonattainment counties to satisfy Colorado's requirement. If you live in a nonattainment county but test in a county that does not require emissions testing, the test will not count toward your registration renewal.
What if I just bought a used car and it fails the test?
You still have 60 days to repair and retest. If you bought the car from a dealer, check your purchase agreement — some dealers offer a short warranty on emissions-related repairs. If you bought from a private seller, you have no recourse through the seller, but the Repair information Program may help if you may have access to by income.
Do I need to test if I am renewing my registration online?
Yes. Online renewal still requires a passing emissions test if you live in a nonattainment county. You must complete the test before you can finish the online renewal process. The testing station will send your pass record to the Division of Motor Vehicles automatically.
What if the testing station says my vehicle cannot be tested?
This is rare but can happen if your vehicle is too damaged to safely connect the diagnostic scanner or if the scanner cannot communicate with your vehicle's computer. Ask the technician what the specific problem is. You may need repairs to the diagnostic system itself before testing is possible. Contact the CDPHE if you believe the station made an error.
How long does a pass certificate last?
A pass is valid for two years from the test date. You can renew your registration anytime during those two years. After two years, you will need a new test to renew again.