What Colorado requires and who has to test

Colorado requires emissions testing for most vehicles registered in the state, but the rules depend on where you live and what you drive. If you register a vehicle in the Denver metro area — which includes Denver, Boulder, Jefferson, Adams, Arapahoe, Douglas, and El Paso counties — you must pass an emissions test every two years. Outside that area, you do not need to test unless your vehicle is more than 25 years old and you are registering it for the first time in Colorado.

Gasoline vehicles, diesel vehicles, and hybrids all test under Colorado's program. Plug-in electric vehicles and fully electric vehicles are exempt. If you own a vehicle that is less than four model years old, you are also exempt for the first test cycle after you buy it — though you will need to test in subsequent years if you keep the vehicle.

The test itself measures tailpipe emissions: nitrogen oxides, carbon monoxide, and particulate matter. You cannot pass with a check engine light on, even if the light is for an unrelated issue. Colorado uses the OBD (on-board diagnostics) test, which reads your vehicle's computer rather than using a separate tailpipe probe.

Key Takeaways

  • The Denver metro area requires emissions testing every two years; the rest of Colorado does not test vehicles under 25 years old.
  • You cannot test with a check engine light illuminated, regardless of what triggered it.
  • Testing costs between $20 and $30 per vehicle and takes about 10 minutes at a certified station.
  • You must renew your registration within 60 days of your test expiration date, and the test results stay valid for two years.
  • If you fail, you have 60 days to fix the vehicle and retest at no additional charge at the same station.

Where to find a testing station and what to bring

Colorado operates through a network of private testing stations, not state-run facilities. You can find stations near you on the Colorado Department of Revenue's website by entering your county. The state lists all certified stations with their addresses and hours. Most are independent repair shops, tire shops, or quick-lube facilities that have been certified to perform the test.

Bring your vehicle registration and a valid photo ID. The station will need your vehicle identification number (VIN), which is on your registration and on the dashboard at the base of the windshield on the driver's side. You do not need to bring proof of previous tests or any service records. The station pulls your test history from the state system.

Testing stations are open year-round, but your test must be completed before your registration expires. If your registration expires on June 30, you must test by June 30. Many people wait until the last month, which creates lines at stations in that final month. Testing earlier in your two-year window avoids the rush.

What happens if you fail the test

If your vehicle fails, the testing station gives you a printed report showing which emissions exceeded the limit. You have 60 days from the test date to fix the vehicle and return to the same station for a retest at no charge. The station keeps your failed test on file and will compare your second test against the same standards.

Common reasons for failure include a faulty oxygen sensor, a malfunctioning catalytic converter, or a leak in the fuel system. A mechanic can read the specific error codes from your vehicle's computer to pinpoint the problem. Some repairs are inexpensive (under $100), while others — like catalytic converter replacement — can cost several hundred dollars.

If you cannot afford the repair within 60 days, you can request a waiver from the Colorado Department of Revenue. The waiver requires proof that you spent at least $375 on repairs or diagnostic work and the vehicle still fails. With a waiver, you can register your vehicle even though it did not pass, but you will have to test again in two years and the vehicle must pass at that time.

Timing your test with registration renewal

Your emissions test and vehicle registration are separate transactions, but they are linked. You cannot renew your registration without a passing test result on file. The test result stays valid for two years from the date you test, not from the date you register.

If your registration expires on June 30, you can test anytime in the 60 days before that date (starting May 1) and use that result to renew. If you test on May 15, your next test will be due on May 15 two years later. You do not have to renew your registration on the same day you test — you can test early and renew closer to your expiration date if you prefer.

You can renew your registration online through the Colorado Department of Revenue website, by mail, or in person at a county clerk's office. Once your test result is in the state system, you can complete registration renewal when ready. Online renewal is the fastest option and takes a few minutes.

What to do before your test appointment

Drive your vehicle for at least 10 minutes before arriving at the testing station. The test measures emissions from a warm engine, and a cold engine produces different readings. If you drive straight from home to the station, your results may be inaccurate.

Make sure your check engine light is off. If it is on, the station will not test your vehicle. You can take your vehicle to a mechanic or auto parts store to have the code read for free or low cost. Some auto parts stores will read the code without charge if you ask. Once you know what triggered the light, you can decide whether to fix it before testing or take it to a mechanic.

Check your tire pressure before you go. Underinflated tires can affect engine performance and emissions readings. Your vehicle's recommended tire pressure is printed on a sticker inside the driver's door jamb, not on the tire itself.

Costs and payment methods

Testing costs between $20 and $30 per vehicle, depending on the station. The state does not set a fixed price; each certified station sets its own fee. Call ahead if you want to know the exact cost at your chosen station, though most are within this range.

Most stations accept cash, debit cards, and credit cards. A few accept only cash, so ask when you call or check the station's listing on the Department of Revenue website. The fee covers one test only. If you fail and need a retest, the retest is free at the same station within 60 days.

If you need a waiver after failing twice, there is no additional fee to request one. You submit the waiver request to the Department of Revenue with proof of repair expenses, and the decision is made within a few weeks.

Frequently Asked Questions

Can I test my vehicle before my registration expires?

Yes. You can test anytime in the 60 days before your registration expires. The test result is valid for two years from the test date, so if you test early, your next test will not be due until two years later. This is useful if you want to spread out your testing and registration renewal across different months.

What if I move out of the Denver metro area?

If you move outside the testing area, you no longer need to test unless your vehicle is more than 25 years old. When you renew your registration at your new county clerk's office, tell them your new address. The state will remove the testing requirement from your registration if you are outside the metro area.

Do I need to test if I just bought a used car in Colorado?

Not when ready. You have until your first registration renewal to pass a test. If you buy a used car and register it for the first time in Colorado, you must test before you renew that registration two years later. However, if the vehicle is less than four model years old, you are exempt from the first test cycle.

What if the testing station says my vehicle cannot be tested?

A station may refuse to test if your check engine light is on, if your vehicle is too new or too old for the program, or if it is not registered in Colorado. If you believe the refusal is incorrect, contact the Colorado Department of Revenue's Air Quality Control Commission. They can clarify whether your vehicle is required to test and direct you to another station if needed.

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

Yes. You can test at any certified station in Colorado, regardless of which county issued your registration. The test result is recorded in the state system under your VIN, so any station can see it when you renew. This is helpful if you travel or move temporarily.