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

Colorado requires an emissions test for most vehicles registered in the state, and the test checks whether your car's exhaust meets state air quality standards. The test itself takes about 10 minutes and costs between $20 and $30, depending on your vehicle type and the testing station.

You need a test if you register a vehicle in Colorado and it was built in 1981 or later. The main exceptions are vehicles registered in certain rural counties (Archuleta, Delta, Dolores, Garfield, Gunnison, Hinsdale, Jackson, Montrose, Moffat, Ouray, Rio Blanco, Routt, and San Juan counties), plus some vehicles that are brand new, heavily modified, or registered as antiques. Diesel trucks over 14,000 pounds also have different rules.

You'll take the test at a Colorado Department of Transportation (CDOT) approved testing station. These are private businesses — repair shops, tire shops, and dedicated emissions testing centers — not government offices. You can find approved stations on the Colorado Air Quality Control Commission website by entering your county.

Key Takeaways

  • Colorado emissions tests cost $20 to $30 and take about 10 minutes at a private testing station approved by the state.
  • You need a test every two years when you renew your registration, unless your vehicle is new, an antique, or registered in one of Colorado's rural counties.
  • The test measures tailpipe emissions through a dynamometer (a machine that simulates driving) or a two-speed idle test, depending on your vehicle's age and type.
  • If your car fails, you have 60 days to fix the problem and retest for free at the same station, or you can appeal the result within 30 days.
  • You cannot register your vehicle without a passing test result, so plan to test before your registration renewal important date.

When you need to take the test and how often

You need an emissions test before you renew your vehicle registration. In Colorado, registration renewal happens every two years, so you'll need a test every two years as well. The test must be completed within 90 days before your registration expires.

If you just moved to Colorado and are registering a vehicle for the first time, you'll need a test as part of that initial registration. If you buy a used car in Colorado, the seller should provide you with a passing test result from the current registration period, but you'll be responsible for getting a new test when that registration expires.

You can take the test at any approved station in the state, not just in your county. If you're near a border, you don't have to test in Colorado — but if you register the vehicle in Colorado, you do need the test before the state will issue your registration.

How the test actually works

The test measures what comes out of your tailpipe. For most vehicles built after 1995, the station uses a dynamometer, which is a machine with rollers that your car drives onto. Your wheels spin on the rollers while the machine simulates city and highway driving, and a probe in your tailpipe measures emissions during that simulated drive. The whole process takes about 10 minutes.

For older vehicles (1981 to 1995), the test is simpler: the station measures emissions while your engine idles at two different speeds, without the dynamometer. This takes less time but is less thorough.

The test checks for nitrogen oxides, carbon monoxide, carbon dioxide, and hydrocarbons — pollutants that contribute to smog and air quality problems. Your car passes if these measurements fall below Colorado's limits. The limits are set by state air quality rules and are stricter in the Denver metro area than in other parts of the state.

What happens if your car fails the test

If your car fails, you'll receive a written report showing which emissions exceeded the limit. You then have 60 days to fix the problem and return to the same testing station for a free retest. You don't pay for the retest — only for the original test.

Common reasons for failure include a faulty oxygen sensor, a loose gas cap, a failing catalytic converter, or engine problems that trigger the check-engine light. A mechanic can read your car's diagnostic codes to pinpoint the issue. Some repairs are inexpensive (a gas cap might cost $10 to $20), while others (a catalytic converter) can cost several hundred dollars.

If you believe the test result is wrong, you can request an appeal within 30 days. You'll need to contact the Colorado Air Quality Control Commission and provide documentation of your appeal. The station will then conduct a second test, and if that test also fails, you'll need to make repairs before you can register your vehicle.

Finding a testing station and preparing for your test

To find an approved testing station, visit the Colorado Air Quality Control Commission website and search by county. The site lists each station's address, phone number, and hours. Call ahead to ask about wait times — some stations are busier than others, especially near registration renewal important date.

Before you go, make sure your car is in reasonable condition. Your check-engine light should not be on (if it is, have a mechanic scan the codes first). Your gas cap should be tight. Your tires should be properly inflated. These straightforward checks can prevent a failure.

Bring your vehicle registration and a photo ID. Some stations may ask for your Vehicle Identification Number (VIN), which is on your registration and on a sticker inside your driver's side door. You don't need an appointment at most stations, but calling ahead can save you time.

What to do if you can't pass the test

If your car repeatedly fails even after repairs, you may be able to get a waiver. Colorado offers a repair cost waiver if you've spent $500 or more on repairs to fix emissions problems within the past two years and the car still fails. To request a waiver, contact the Colorado Air Quality Control Commission with documentation of your repair costs and failed test results.

If you're granted a waiver, you can register your vehicle without a passing test for that registration period. However, you'll need to test again at your next renewal. A waiver is not permanent — it's a one-time relief when repair costs become unreasonable.

If your vehicle is very old or has serious engine problems, you might also consider whether it makes financial sense to repair it. Some people find that the cost of repairs exceeds the car's value. In that case, you'd need to either sell the car, scrap it, or move it out of state.

Emissions testing in different Colorado counties

Colorado's emissions rules vary by region. The Denver metro area (Denver, Boulder, Jefferson, Adams, Arapahoe, Douglas, and El Paso counties) has stricter standards than the rest of the state because air quality is worse in that region. If you live in the metro area, your car must meet tighter emissions limits.

Rural counties listed earlier in this article don't require emissions testing at all. If you register a vehicle in one of those counties, you won't need a test. However, if you move from a rural county to a metro area, you'll need to test before you can register the vehicle in the new location.

Some counties also have different testing requirements for diesel vehicles. If you own a diesel truck or SUV, check with your local testing station about whether your vehicle needs a test and what type of test applies.

Frequently Asked Questions

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

Yes. You can take your emissions test at any approved station in Colorado, regardless of which county you live in. However, the emissions standards that explore are based on where you register the vehicle, not where you test it. If you register in Denver, your car must meet Denver metro standards even if you test in a rural county.

What if I just bought a used car and it fails the emissions test?

The seller should have provided a passing test from the current registration period. If they didn't, that's a problem — you may have a claim against them depending on your purchase agreement. If the car fails your test, you have 60 days to repair it and retest for free. Keep all repair receipts in case you need to request a waiver later.

Do I need to test my car if I'm only registering it for a few months?

Yes. Colorado requires an emissions test before registration, regardless of how long you plan to keep the vehicle registered. There's no short-term registration option that skips the test. If you're only keeping the car briefly, you might still need to test before you can register it.

What happens if my registration expires before I get a passing test?

You cannot legally drive the vehicle once your registration expires. You must test and pass before your registration renewal important date. If you're close to the important date and worried your car might fail, test early so you have time to make repairs if needed.

Is there a way to avoid the emissions test?

The only ways to avoid testing are to register your vehicle in a rural county that doesn't require it, to register a brand-new vehicle (which are exempt for the first few years), or to register an antique vehicle. If your vehicle doesn't fall into one of these categories and you register it in Colorado, you need a test.