What Colorado's emission test measures and who needs one

Colorado requires an emission test for most vehicles registered in the state, but the rules depend on where you live and what you drive. If you live in the Denver metro area, the North Front Range, or the Pueblo area, your vehicle must pass an emission test every two years. If you live elsewhere in Colorado, you do not need an emission test — your registration renewal is simpler.

The test itself checks whether your vehicle's exhaust meets state pollution limits. A technician connects a machine to your vehicle's diagnostic port (usually under the steering wheel) and reads the data your car's computer has recorded. The machine measures nitrogen oxides, particulate matter, and other pollutants. Diesel vehicles and gasoline vehicles have different standards, and newer cars (usually 1996 and later) are tested differently than older ones.

You do not need a test if your vehicle is brand new (typically exempt for the first four years), if it is registered as a motorcycle, or if it is a vehicle you only drive occasionally and have registered as such. Electric vehicles are also exempt. If you are unsure whether your vehicle needs testing, the Colorado Department of Public Health and Environment website has a lookup tool where you enter your vehicle information.

Key Takeaways

  • Emission testing is required every two years in the Denver metro, North Front Range, and Pueblo areas, but not in other parts of Colorado.
  • The test takes about 15 minutes and costs between $20 and $30 depending on your vehicle type and the testing station.
  • You can visit any Colorado Department of Revenue-certified emission testing station; they are not run by the state itself.
  • If your vehicle fails, you have 60 days to repair it and retest at no additional charge before your registration becomes invalid.
  • Newer vehicles (usually 1996 and later) are tested using your car's onboard computer; older vehicles may require a different test method.

Where to find a testing station and what to bring

Colorado does not run emission testing stations itself. Instead, the state certifies private shops — repair shops, tire shops, quick-lube places, and dedicated testing centers — to perform the test. You can find a certified station by searching the Colorado Department of Revenue's online station locator, which shows locations near you, their hours, and whether they accept walk-ins or require an appointment.

Bring your vehicle registration and a photo ID. Some stations may ask for your vehicle's VIN (vehicle identification number), which is on your registration and on the dashboard. If your vehicle's check engine light is on, the test will fail automatically, so have that repaired first. You do not need to bring any documents related to previous tests or repairs.

The test itself takes about 15 minutes. The technician will connect a diagnostic machine to your vehicle, run the test, and print a result. If you pass, the result is sent electronically to the Colorado Department of Revenue, and your registration is cleared. If you fail, you receive a printed report showing which emissions standards your vehicle did not meet.

What happens if your vehicle fails the test

A failed test does not when ready invalidate your registration, but you have 60 days to fix the problem and retest. During those 60 days, you can still drive your vehicle legally. The test report will tell you which emissions systems are not working properly — for example, "oxygen sensor malfunction" or "catalytic converter failure."

Take the report to a repair shop. The shop can use the information to diagnose and fix the problem. Once repaired, you can return to any certified testing station and retest at no additional charge (the retest is free; you pay only if you visit a different station). If you pass the retest, the result is sent to the state and your registration is valid.

If you do not retest within 60 days, your registration becomes invalid and you cannot legally drive the vehicle. If you have already paid for registration and then fail the test, you do not get a refund, but you can request a registration extension while you repair the vehicle. Contact the Colorado Department of Revenue to request an extension if you need more than 60 days.

Cost and timing for registration renewal

The emission test itself costs between $20 and $30, depending on whether your vehicle is gasoline or diesel and whether it is older or newer. This is a separate fee from your vehicle registration renewal fee. Some stations charge a flat rate; others charge slightly more for diesel vehicles or for vehicles that require additional testing steps.

You must pass the emission test before you renew your registration. In Colorado, you renew registration online through the Colorado Department of Revenue website, by mail, or in person at a county clerk's office. The online system will not let you complete renewal if your vehicle has not passed a current emission test (in the required counties).

Plan to take the test at least two weeks before your registration expires, in case you fail and need time to repair and retest. If your registration has already expired and you have not yet tested, you can still test and renew, but you may owe a late fee on top of the registration renewal cost.

Vehicles exempt from testing and special situations

New vehicles are typically exempt from emission testing for their first four years of registration in Colorado. After that, they enter the regular testing cycle. Vehicles registered as "occasional use" or "collector" vehicles may have different rules — check with your county clerk about whether your registration type requires testing.

If you have a vehicle with a gross vehicle weight rating (GVWR) over 14,000 pounds, it may be subject to different emission standards or may not require testing at all. Heavy trucks and commercial vehicles have separate rules. If you are unsure, the Colorado Department of Public Health and Environment website has detailed information by vehicle class.

If you move to Colorado from another state and your vehicle is registered out of state, you have until your out-of-state registration expires to obtain a Colorado registration. Once you register in Colorado, the emission testing requirement applies if you live in a required county.

What to do if your vehicle has an active check engine light

If your vehicle's check engine light is on, it will fail the emission test automatically. The light indicates that your vehicle's onboard diagnostic system has detected a problem — usually with the engine, emissions system, or transmission. You must have the problem diagnosed and repaired before you can pass the test.

Take your vehicle to a repair shop and have them read the diagnostic trouble code using a scanner. The code will tell the technician what system is malfunctioning. Common causes include a loose gas cap, a faulty oxygen sensor, or a catalytic converter problem. Once repaired, the technician should clear the code and verify that the light does not return.

After repair, you can return to a testing station and retest. If the light comes back on during the test, you will fail again. If it stays off and your emissions are within limits, you will pass.

Understanding the difference between older and newer vehicle tests

Vehicles from 1996 onward have an onboard diagnostic system (OBD-II) that stores emissions data. The emission test for these vehicles is straightforward: the technician connects to the diagnostic port and reads the data your car's computer has already recorded. The test takes a few minutes and does not require your vehicle to run on a dynamometer (a machine that simulates driving).

Vehicles older than 1996 do not have this system. If you own a pre-1996 vehicle in a county that requires emission testing, you may need to take it to a shop that performs older-vehicle testing, which may involve a tailpipe test or a dynamometer test. These tests are less common and may cost more. Check with your local testing station about whether they test pre-1996 vehicles.

Diesel vehicles, whether old or new, have their own testing procedures because they produce different emissions than gasoline vehicles. Most certified stations test both gasoline and diesel vehicles, but confirm this before you visit.

Frequently Asked Questions

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

Yes. You can visit any certified testing station in Colorado, regardless of which county you live in. However, your vehicle must meet the emission standards of the county where it is registered. If you are registered in Denver but test in a rural county, the test will still use Denver's standards.

What if I just moved to Colorado and my vehicle is still registered in another state?

You have until your out-of-state registration expires to register your vehicle in Colorado. Once you register here, you must follow Colorado's emission testing rules if you live in a required county. You do not need to test when ready upon moving; you test when you renew your registration.

Do I need an emission test if I am renewing my registration online?

If you live in the Denver metro, North Front Range, or Pueblo area, yes — you must pass an emission test before you can complete your online registration renewal. The system will not let you finish without a passing test result. If you live elsewhere in Colorado, no test is required.

How long does a retest take if my vehicle fails?

The retest itself takes about 15 minutes, the same as the initial test. However, the time between failure and retest depends on how long repairs take. You have 60 days from the date of failure to retest, so plan your repair schedule accordingly.

What if I sell my vehicle before the emission test is due?

The emission test requirement transfers to the new owner. If the vehicle is due for a test and the new owner wants to register it in Colorado, they must pass the test before registration is complete. As the seller, you are not responsible for the test; the buyer must handle it.