What Colorado's emissions test checks and who has to take it

Colorado requires an emissions test for most vehicles registered in the state, though the exact rules depend on where you live and what year your vehicle was made. The test measures what comes out of your tailpipe — specifically nitrogen oxides, particulate matter, and hydrocarbons — to make sure your vehicle meets state air quality standards. Vehicles from 1975 and newer generally need testing, but some counties have stricter rules than others.

The Denver metro area (which includes Adams, Arapahoe, Boulder, Broomfield, Douglas, El Paso, Jefferson, Larimer, and Weld counties) has the most stringent requirements because of air quality concerns. If you live outside these counties, your vehicle may not need an emissions test at all, or you may only need one every other year. You can check your county's specific rules on the Colorado Department of Public Health and Environment website or by calling your local emissions testing center.

Key Takeaways

  • Colorado's emissions test measures tailpipe pollution and is required in most counties, though Denver metro counties have stricter rules than rural areas.
  • Your vehicle must pass the test before you can renew your registration, and the test costs between $20 and $30 depending on your vehicle type and testing location.
  • You can take the test at any state-certified emissions testing station, and results are sent directly to the Colorado Department of Revenue so you do not have to submit them yourself.
  • If your vehicle fails, you have until your registration expires to fix the problem and retest, though some repairs may be expensive.

Where to find a testing station and what to bring

Colorado has hundreds of certified emissions testing stations across the state, run by private companies under state oversight. You can find one near you by visiting the Colorado Department of Public Health and Environment website and entering your zip code, or by searching online for "emissions testing near me" — most stations are at repair shops, service stations, or dedicated testing centers.

When you go to test, bring your vehicle registration and a valid photo ID. Some stations may ask for your vehicle's VIN (vehicle identification number), which is on your registration or on the driver's side of your dashboard. You do not need to make an appointment at most stations, though calling ahead during busy seasons (typically fall and winter) can save you a wait. The test itself takes about 10 to 15 minutes.

How the test works and what happens if you pass

The emissions test is straightforward: a technician plugs a probe into your vehicle's tailpipe while the engine runs through a short cycle. The machine measures the pollutants coming out and compares them to Colorado's limits. For most vehicles, the test is non-invasive and does not require any work on your part beyond showing up with a vehicle in normal running condition.

If your vehicle passes, the testing station sends the results electronically to the Colorado Department of Revenue within 24 hours. You do not have to do anything else — your registration renewal will go through. The test is valid for one year from the date you take it, so you will need to test again when you renew your registration the following year.

What to do if your vehicle fails the test

If your vehicle fails, you will receive a report showing which pollutants exceeded the limit. Common reasons for failure include a faulty oxygen sensor, a problem with the catalytic converter, a check engine light that is on, or straightforward an engine that needs a tune-up. The testing station will give you a copy of the results, which you can take to a mechanic to diagnose the problem.

You have until your registration expires to fix the vehicle and retest at no additional charge — most stations will retest you for free if you come back within a certain window (usually 30 to 60 days). Some repairs are inexpensive, like replacing spark plugs or an air filter, but others, like catalytic converter replacement, can cost several hundred dollars. If the repair cost is very high, you may be able to request a waiver from your county, though this is not may provide.

Emissions testing waivers and repair information

If your vehicle fails and the repair cost exceeds a certain threshold — typically $500 to $700, though this varies by county — you may be able to get a waiver that lets you renew your registration without passing the test. To request a waiver, you will need to get a repair estimate from a mechanic and submit it to your county's emissions program office. The waiver is not automatic, and rules differ between counties.

Some counties also have repair information programs that help pay for emissions-related fixes if your household income is below a certain level. Contact your local county health department or the Colorado Department of Public Health and Environment to ask whether your county offers this program and what the income limits are.

Timing and registration renewal

Your emissions test must be completed before your vehicle registration expires. The test is valid for one year, so if you test in January, that result is good through the following January. You can test up to 90 days before your registration expires, which gives you a window to plan ahead.

If your registration expires before you pass the test, you cannot legally drive the vehicle. If you fail the test and need time to make repairs, contact your county assessor's office about a temporary registration extension while you work on the vehicle — this is not may provide, but some counties will grant a short extension if you can show proof that you have scheduled a repair.

Denver metro area rules and stricter standards

If you live in the Denver metro area, your vehicle must meet stricter emissions standards than the rest of Colorado. The test is more sensitive, and vehicles that might pass in other parts of the state could fail here. Additionally, Denver metro residents must test every year, while some rural counties only require testing every other year or not at all.

Diesel vehicles in the Denver metro area face even stricter rules and may be subject to additional testing or restrictions. If you own a diesel vehicle, check with your testing station or county office about whether your vehicle meets current standards, as rules have tightened in recent years.

Frequently Asked Questions

Can I test my vehicle before my registration expires?

Yes. You can test up to 90 days before your registration expires, and the result will be valid for one year from the test date. This gives you time to plan and schedule the test during a less busy period if you prefer.

What if I just bought a used car and do not know if it will pass?

You can take it to any testing station to find out. If it fails, you have until your registration expires to fix it and retest. Many people test a used car soon after purchase so they know what repairs, if any, are needed before the registration important date.

Do I have to test if I just moved to Colorado?

You will need to test when you register your vehicle in Colorado for the first time. The registration office will tell you whether your vehicle needs an emissions test based on your county and your vehicle's year. If you move from one Colorado county to another, you may need to retest if the new county has stricter rules.

What if my vehicle has a check engine light on?

Most testing stations will not test a vehicle with an active check engine light because the light usually indicates an emissions-related problem. You will need to have the problem diagnosed and fixed first, then clear the light before you can test.

How much does the emissions test cost?

The cost is typically between $20 and $30, depending on your vehicle type and the testing station. Diesel vehicles and heavy-duty trucks may cost more. If you fail and need to retest, the retest is usually free if you return within 30 to 60 days.