What Denver's emissions test requires and where to take it

Denver requires an emissions test every two years for most vehicles, and you'll take it at an Emissions Testing Center operated by the Colorado Department of Public Health and Environment. The test measures what comes out of your tailpipe — carbon monoxide, nitrogen oxides, and particulate matter — to confirm your vehicle meets state air quality standards. You cannot renew your vehicle registration without a passing test result.

The test itself takes about 10 to 15 minutes. A technician will plug a diagnostic scanner into your vehicle's onboard computer port (located under the dashboard on the driver's side) and run your engine through a standardized cycle. You'll need your vehicle registration and proof of ownership, and your vehicle's check engine light cannot be on.

Denver has multiple testing centers across the metro area. You can find the current list and book an appointment at Colorado.gov/CDPHE under the vehicle emissions section, or call the emissions hotline for walk-in locations. Some centers require appointments; others accept walk-ins during specific hours. Appointment slots fill up, especially before the registration important date, so booking ahead saves time.

Key Takeaways

  • Denver emissions tests are required every two years and must be completed before you can renew your vehicle registration.
  • The test takes 10 to 15 minutes at a state-operated Emissions Testing Center and costs between $20 and $30, depending on the location.
  • Your vehicle's check engine light must be off, and you'll need your registration and proof of ownership to complete the test.
  • You can find testing center locations and book appointments through Colorado.gov/CDPHE or by calling the state emissions hotline.

Cost and what happens if you fail

The emissions test costs between $20 and $30 at most Denver-area centers. Some centers charge slightly different amounts, so confirm the fee when you book. If you pass, you'll receive a printed test result when ready, and the result is automatically reported to the Colorado Division of Motor Vehicles — you don't have to submit it yourself.

If your vehicle fails, the test report will show which pollutants exceeded the limit. You'll have the option to retest at no additional charge within 30 days at the same center. Before retesting, you'll need to repair the issue — common failures involve a faulty oxygen sensor, a clogged fuel injector, or a problem with the catalytic converter. A mechanic can read your vehicle's diagnostic code (the same code the emissions test scanner reads) to pinpoint what needs fixing.

If you repair the vehicle and retest within 30 days, you pay only the original test fee. If you wait longer than 30 days, you'll pay the full fee again. Some repair shops offer a "retest may provide" — they'll cover the retest fee if the repair doesn't fix the emissions problem, though this varies by shop.

Timing: when to test before your registration expires

Your emissions test must be completed before your vehicle registration expires. You can take the test up to 120 days before your registration renewal date. Testing early gives you a buffer in case you fail and need time for repairs, but don't test too far ahead — if you fail and the 30-day retest window closes before your registration important date, you'll have to pay for a new test.

The safest approach is to test 60 to 90 days before your registration expires. That gives you time to repair and retest if needed, and still leaves a few weeks as a safety margin. If your registration expires on June 30, for example, test between mid-March and mid-April.

You can check your registration expiration date on your registration card or through the Colorado DMV website. If you're unsure whether your vehicle is due for an emissions test, the DMV website will tell you — not all vehicles require testing every year, and some are exempt entirely.

Which Denver vehicles are exempt from emissions testing

Vehicles registered in Denver County are generally required to test, but there are exceptions. Vehicles that are less than 6 model years old are exempt — a 2020 model registered in 2024 would not need to test yet. Vehicles over 25 model years old are also exempt, as are electric vehicles and some hybrid models.

Vehicles with a gross vehicle weight rating over 14,000 pounds (most commercial trucks) follow different rules and may test at a separate facility. If you're unsure whether your vehicle is exempt, enter your vehicle information on the Colorado DMV website or call the emissions hotline — they can confirm in seconds.

What to bring and prepare before you go

Bring your vehicle registration card and a photo ID. The registration card shows your vehicle's VIN, which the testing center will verify matches the vehicle you're driving. You don't need to bring your title or proof of insurance, though having them won't hurt.

Before you arrive, make sure your check engine light is off. If it's on, the test center will refuse to test you — the light indicates a diagnostic code is stored, and the test cannot proceed until that code is cleared. A mechanic can clear it, or in some cases driving the vehicle normally for a few days will clear it if it was a temporary sensor glitch. Don't try to disconnect the battery or use a code reader to clear it yourself; the test center's scanner will detect that.

Fill your gas tank or at least have a quarter tank of fuel. The test runs your engine, and you need enough fuel to complete it. Arrive with a clean windshield so the technician can see your odometer reading if needed.

Retesting and repair shops that may provide results

If you fail the emissions test, you have two paths: repair the vehicle yourself at a shop of your choice, or use a repair shop that offers a retest may provide. A retest may provide means the shop will pay for your second emissions test if the repair doesn't fix the problem. This is common at larger shops and dealerships, though not universal.

Ask the shop upfront whether they offer a retest may provide and what it covers. Some shops may provide only specific repairs (like oxygen sensor replacement) but not others. Get the may provide in writing before you authorize the repair. The may provide protects you if the repair doesn't solve the emissions issue, but it doesn't cover repairs that fail for other reasons — for example, if you hit a pothole and damage the new part.

You can also take your vehicle to any mechanic, get it repaired, and retest on your own. This is cheaper if the repair works the first time, but it leaves you paying for a second test if it doesn't. Weigh the cost of the repair against the cost of a potential retest fee to decide which route makes sense for your situation.

What to do if you can't test before your registration expires

If your registration expires before you can complete the emissions test, you cannot legally drive the vehicle. Driving with an expired registration is a traffic violation and can result in a fine. However, you can still test after your registration expires — the test itself is not time-limited, only the registration is.

If this happens, you'll need to renew your registration after you pass the emissions test. Go to a Colorado DMV office or use the online renewal system once you have your passing test result. The test result is valid for 120 days, so you have that window to renew. You'll pay a late renewal fee in addition to the standard registration fee, so it's worth testing before the important date to avoid that extra cost.

Frequently Asked Questions

Can I test in a different Colorado county if I live in Denver?

No. Your vehicle must be tested in the county where it's registered. Denver County has its own testing centers and requirements. If you've recently moved to Denver from another county, you'll need to update your registration address with the Colorado DMV before testing.

What if my vehicle has a check engine light that won't turn off?

The testing center will not test your vehicle until the light is off. A mechanic can read the diagnostic code and repair the underlying problem, which usually turns the light off. Once it's off, you can retest. Some auto parts stores will read the code for free, which can help you understand what needs fixing.

Do I need to make an appointment or can I just walk in?

It depends on the testing center. Some require appointments and others accept walk-ins during specific hours. Check the Colorado.gov/CDPHE website for your nearest center's hours and policy. Booking an appointment ahead of time is faster and guarantees a slot, especially during busy seasons.

How long does a passing test result stay valid?

Your passing emissions test result is valid for 120 days. You must renew your vehicle registration within that window. If you don't renew within 120 days, you'll need a new emissions test before you can renew your registration.

What if I fail the test twice?

You can retest as many times as needed within the 30-day window after your first test. If you fail a second time, the same 30-day retest period applies. However, if you're failing repeatedly, the underlying problem is likely more serious — a mechanic should diagnose it rather than guessing at repairs.