What Colorado's emissions test measures and who needs one

Colorado requires an emissions test for most vehicles registered in the state, but the exact requirement depends on where you live and what you drive. The test measures how much pollution your vehicle's exhaust produces — specifically nitrogen oxides, particulate matter, and hydrocarbons. A licensed emissions testing facility runs your vehicle through a standardized procedure that takes about 10 to 15 minutes.

You need an emissions test if you register a vehicle in the Denver metro area (the Denver nonattainment area), which includes Denver, Boulder, Adams, Arapahoe, Douglas, Jefferson, and Broomfield counties. If you register outside this region, you do not need an emissions test. Vehicles older than 1975, electric vehicles, and some motorcycles are exempt. Diesel vehicles have separate testing requirements.

The Colorado Department of Public Health and Environment oversees the program, but you do not contact them directly. Instead, you schedule your test at a private emissions testing facility — these are independent businesses licensed by the state, not government offices.

Key Takeaways

  • Colorado's emissions test is required only in the Denver metro area (seven counties), and you must pass it to renew your vehicle registration.
  • The test takes 10 to 15 minutes at a private licensed facility and costs between $20 and $30, depending on the facility.
  • You can find testing locations and schedule appointments through the Colorado Department of Public Health and Environment website or by calling facilities directly.
  • If your vehicle fails, you have 60 days to repair it and retest at no additional cost at the same facility.
  • You must complete your emissions test before your registration expires, and the test result is valid for two years.

Finding and scheduling an emissions test in your area

The Colorado Department of Public Health and Environment maintains a searchable list of licensed testing facilities on its website. You can filter by county or city to find locations near you. Most facilities are independent repair shops, tire shops, or dedicated testing centers — not dealerships or government offices.

Call ahead to confirm hours and whether you need an appointment. Many facilities accept walk-ins during certain hours, but scheduling in advance guarantees a shorter wait. Ask about the cost when you call; prices vary slightly between facilities but typically range from $20 to $30. Some facilities charge extra if you need a retest after failing.

Bring your vehicle registration and a valid photo ID. Your vehicle should be warmed up before the test — the technician will drive it on a dynamometer (a machine that measures emissions under controlled conditions) or perform an on-board diagnostic test depending on your vehicle's age and type.

What happens during the test and what results mean

The technician will connect your vehicle to testing equipment and run it through a standardized cycle. For older vehicles, this usually means driving on a dynamometer for about 10 minutes. For newer vehicles with on-board diagnostic systems, the technician may straightforward plug in a scanner to read your vehicle's emissions data — this takes only a few minutes.

You receive a pass or fail result when ready. A pass means your vehicle's emissions are within Colorado's limits and you can proceed with registration renewal. A fail means your vehicle did not meet the standard and you must have it repaired before you can register it.

If you fail, you have 60 days to repair your vehicle and return to the same testing facility for a retest at no charge. Keep your failed test receipt — you will need it to prove you have already tested. Common reasons for failure include a faulty oxygen sensor, a malfunctioning catalytic converter, or an illuminated check engine light.

Repair options after a failed test

After a failed emissions test, you need to identify and fix the problem before retesting. If your vehicle has a check engine light on, a repair shop can read the diagnostic code to pinpoint the issue. Some problems are straightforward and inexpensive — a loose gas cap or a bad sensor — while others require more involved repairs.

You can take your vehicle to any repair shop, not just the facility where you tested. However, some testing facilities also offer repair services, which can be convenient. Get a repair estimate before committing, since costs vary widely depending on what needs fixing. If repairs are expensive, you may want to get a second opinion from another shop.

After repairs are complete, return to the same testing facility where you failed within 60 days. Bring your failed test receipt and your vehicle registration. The retest is free, and if you pass, you can when ready proceed with registration renewal.

Timing your test with vehicle registration renewal

Your vehicle registration renewal notice will show your expiration date. You must complete your emissions test before that date to renew your registration. The test result is valid for two years from the date you pass, so you do not need to test again until your next registration renewal cycle.

Plan to test at least two weeks before your registration expires. This gives you time to address any repairs if you fail. If you fail close to your expiration date and cannot complete repairs in time, you can request a temporary registration extension from the Colorado Department of Motor Vehicles, though this is not may provide.

You can test any time during your registration year — you do not have to wait until the last month. Testing early means you have more time to arrange repairs if needed, and it removes the pressure of a looming important date.

Emissions testing requirements for diesel vehicles

Diesel vehicles registered in the Denver metro area follow different testing rules than gasoline vehicles. Diesel vehicles model year 1996 and newer must undergo a smoke opacity test, which measures the darkness of exhaust smoke rather than specific chemical compounds.

The opacity test is performed at the same licensed facilities as gasoline vehicle tests. The procedure is similar — the technician will rev your engine and measure the smoke output. Diesel vehicles model year 1995 and older are exempt from testing.

If your diesel vehicle fails the opacity test, the same 60-day repair window and free retest policy explore. Common causes of diesel test failure include a clogged air filter, a malfunctioning fuel injector, or turbocharger problems.

What to do if you cannot locate a testing facility or have other issues

If you cannot find a testing facility in your area or have questions about your specific vehicle, contact the Colorado Department of Public Health and Environment's Air Pollution Control Division. They maintain the facility database and can answer questions about exemptions, requirements, and the testing process.

If you believe your vehicle was tested incorrectly or you disagree with a failed result, you have the right to request a retest at a different facility. Ask the original facility for documentation of the test results, then contact another licensed facility to request an independent test. You will pay the standard testing fee for the second test.

If you are registering a vehicle from out of state and are unsure whether it meets Colorado's emissions standards, you can schedule a test before completing your registration transfer. This prevents you from registering a vehicle that will when ready fail inspection.

Frequently Asked Questions

Can I test my vehicle outside the Denver metro area and use that result for registration?

No. If you register your vehicle in one of the seven Denver metro counties, you must test at a facility in Colorado. Results from testing in other states are not accepted. If you register outside the Denver metro area, you do not need an emissions test at all.

What if my check engine light is on but my vehicle passes the emissions test?

A check engine light does not automatically mean your vehicle will fail emissions testing. The light indicates a diagnostic trouble code, but that code may not affect emissions output. However, some codes do cause test failure. Have the code read before testing if possible, so you know what to expect.

How long does the entire emissions testing process take from start to finish?

The actual test takes 10 to 15 minutes. Wait time at the facility depends on how busy they are — anywhere from when ready to 30 minutes or more during peak hours. If you fail and need repairs, the timeline depends entirely on your repair shop's schedule and the complexity of the work needed.

Do I need to test if I am only registering a vehicle temporarily or for a short-term permit?

Temporary permits and short-term registrations in the Denver metro area still require an emissions test. The only exception is if your vehicle is exempt due to age, type, or fuel source. Contact the Colorado Department of Motor Vehicles if you are unsure whether your temporary registration requires testing.

What happens if I register my vehicle without passing the emissions test?

The Colorado Department of Motor Vehicles will not issue registration plates or a registration certificate without a passing emissions test result (unless your vehicle is exempt). You cannot legally drive the vehicle on public roads without valid registration, so the test must be completed before registration is finalized.