Colorado requires an emissions test every two years for most vehicles, and you'll need to pass it before you can renew your registration

Colorado's emissions test measures how much pollution your vehicle produces. The state runs this program through the Department of Revenue, and it applies to most gasoline-powered cars, trucks, and SUVs registered in certain counties. You must pass the test before your registration expires, or you cannot legally renew it.

The test itself takes about 10 minutes and costs between $20 and $30 depending on your vehicle type and which testing station you visit. You'll drive onto a dynamometer (a machine that measures your engine's output), and sensors will check your exhaust for nitrogen oxides and particulate matter. If you pass, you get a certificate that's valid for two years. If you fail, you have options to repair your vehicle and retest.

Key Takeaways

  • Colorado requires emissions testing every two years for vehicles in the Denver metro area and other designated counties, but not statewide.
  • You must pass the test before you can renew your vehicle registration, and the test costs $20 to $30.
  • If your vehicle fails, you have 60 days to repair it and retest at no additional charge under Colorado's repair information program.
  • Diesel vehicles, motorcycles, and vehicles over 25 years old are exempt from the emissions requirement.
  • You can find a testing station through the Colorado Department of Revenue website or by calling your local air quality office.

Which Colorado counties require emissions testing

Not all of Colorado requires emissions testing. The state focuses the program on areas with air quality concerns, primarily the Denver metro region and surrounding counties. Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, El Paso, Jefferson, Larimer, and Weld counties all require it. If you live in a county not listed here, you do not need to test.

If you're unsure whether your county requires testing, check the Colorado Department of Revenue's Air Quality Control Commission website or call your county clerk's office. They can confirm your testing requirement in seconds. If you move to a county that doesn't require testing, you'll stop needing to test once your current certificate expires.

How to find a testing station and schedule your test

Colorado has about 150 emissions testing stations across the state, run by private operators under state contract. You can find one near you through the Colorado Department of Revenue website—search by county or city, and you'll see a list with addresses, phone numbers, and hours. Most stations are open during business hours and on Saturdays, though hours vary.

You do not need an appointment at most stations; you can drive in during business hours and wait your turn. Some stations do take reservations, which can save you time during busy seasons like the months before registration renewal important date. Call ahead if you want to confirm wait times or book a slot. Bring your vehicle registration and a valid ID.

What happens if your vehicle fails the emissions test

If your vehicle fails, you'll receive a detailed report showing which emissions standards it didn't meet. You then have 60 days to repair the vehicle and retest at no additional charge. This means your second test is free—you only pay the initial test fee.

Colorado's repair information program can help if the repairs are expensive. If your vehicle fails and repairs cost more than $500, you may be able to get a waiver that lets you renew your registration anyway. You'll need to document the repair estimate and submit it to the testing station or the state. Not all vehicles may have access to, and the waiver process has specific requirements, so ask the testing station about your options when you get your failure report.

Vehicles exempt from Colorado emissions testing

Diesel vehicles are exempt from the standard emissions test, though Colorado has separate rules for diesel trucks in certain counties. Motorcycles and mopeds do not require testing. Vehicles manufactured before 1975 are also exempt, as are vehicles over 25 years old in some cases—the exact cutoff depends on your county and the current year.

Electric vehicles do not require emissions testing because they produce no tailpipe emissions. If you own a hybrid, it still must test unless it's a plug-in hybrid that's over 25 years old. When you go to renew your registration, the system will tell you whether your vehicle needs to test based on its model year and fuel type.

Preparing your vehicle for the emissions test

Before you test, make sure your vehicle is in reasonable running condition. The test measures what comes out of your tailpipe, so a vehicle with a check engine light, a loose gas cap, or worn spark plugs is more likely to fail. If your check engine light is on, get it scanned at a mechanic first—that's often a sign of an emissions system problem.

Warm up your engine for a few minutes before you arrive at the testing station. The test works best when your engine is at normal operating temperature. You don't need to do anything special beyond that—the testing station will handle the rest. If your vehicle has been sitting unused for weeks, drive it for 20 minutes or so before testing to clear out any buildup.

Renewing your registration after passing the test

Once you pass the emissions test, you'll get a certificate with a confirmation number. You can then renew your vehicle registration online through the Colorado Department of Revenue website, by mail, or in person at your county clerk's office. The system will ask for your emissions test confirmation number, so keep that certificate or write down the number.

You must renew your registration before the expiration date on your current registration. If your registration expires before you pass the test, your vehicle is no longer legal to drive. If you're close to your expiration date, test early—don't wait until the last week.

Frequently Asked Questions

Can I renew my registration without passing the emissions test?

No. If your vehicle is in a county that requires testing, you cannot renew your registration without a passing emissions certificate. The system will not allow it. If you fail the test, you have 60 days to repair and retest before your registration expires.

What if I just moved to Colorado from another state?

You'll need to register your vehicle in Colorado within 30 days of moving. If you're in a county that requires emissions testing, you'll need to pass the test before you can complete registration. Out-of-state registrations don't count—you must test under Colorado's rules.

How much does it cost to repair a vehicle that failed the emissions test?

Repair costs vary widely depending on what's wrong. Common fixes include replacing spark plugs, fixing a vacuum leak, or replacing an oxygen sensor—these might cost $100 to $300. More serious problems like a catalytic converter replacement can cost $500 or more. Get a repair estimate before you decide whether to fix it or pursue a waiver.

Do I have to test at the same station where I failed?

No. You can retest at any Colorado emissions testing station, not just the one where you failed. If you want to try a different station, that's your choice. The retest is free regardless of which station you use.

What if my vehicle is registered in one county but I live in another?

Test in the county where your vehicle is registered, not where you live. If your registration is in a county that requires testing, you must test. If it's in a county that doesn't require testing, you don't have to, even if you live in a county that does.