What Denver requires and when you need to test

Denver requires emissions testing for most vehicles registered in the city and surrounding counties that are part of the Denver metro area. You must test every two years if your car is newer than 1981, or every year if it is older. The test checks whether your vehicle's exhaust meets Colorado air quality standards — specifically measuring nitrogen oxides, particulate matter, and other pollutants.

You do not need to test if your vehicle is brand new (usually the first four model years are exempt), registered as a classic or antique car, or powered entirely by electricity. Diesel vehicles have their own testing protocol. Hybrids and plug-in hybrids follow the standard gasoline vehicle schedule.

Your registration renewal notice will tell you whether your car is due. If you are moving to Denver from another state, you will need to pass emissions before you can register your vehicle in Colorado. The test must happen before your registration expires, or you risk a fine and cannot legally drive the vehicle.

Key Takeaways

  • Denver emissions testing is required every two years for most vehicles, or annually for cars made before 1981.
  • You can test at any Colorado Department of Transportation-approved testing station, which you can find through the state's online station locator.
  • The test costs between $25 and $35 depending on the station, and you receive results when ready on the same day.
  • If your vehicle fails, you have 60 days to repair it and retest at no additional charge at the same station.
  • Vehicles that fail twice in a row may be subject to additional inspections or restrictions on registration renewal.

Finding a testing station and what to bring

The Colorado Department of Transportation maintains a searchable list of approved emissions testing stations on its website. You can filter by location, hours, and whether the station offers drive-through service. Most stations are independent repair shops, tire shops, or dedicated testing centers — not dealerships. Many are open early morning and evening to accommodate working drivers.

Bring your vehicle registration card or proof of registration, your driver's license, and payment (cash or card, depending on the station). You do not need an appointment at most stations, though some busier locations accept them. The actual test takes 10 to 15 minutes. The technician will plug a probe into your vehicle's exhaust system while the engine runs through a short cycle, measuring what comes out.

Your vehicle must be in reasonably good mechanical condition to test. If your check engine light is on, the station may refuse to test until you have the problem diagnosed. If your vehicle has not been driven for several days, warm it up for a few minutes before arriving, as a cold engine can fail even if the vehicle would pass when warm.

Understanding your test results

You will receive a printed receipt showing whether your vehicle passed or failed. A pass means your emissions are within Colorado's limits and your registration can proceed. The receipt is valid for 30 days, so you have time to complete your registration renewal after testing.

A fail means your vehicle's emissions exceeded the standard for at least one pollutant. The receipt will show which pollutant failed and by how much. Common reasons for failure include a faulty oxygen sensor, a clogged fuel injector, worn spark plugs, or a problem with the catalytic converter. You do not need to know the cause when ready — you have 60 days to have the vehicle repaired and retested.

If you retest within 60 days at the same station, the retest is free. You can have the repair done anywhere — a dealership, an independent mechanic, or yourself if you have the skills. Many repair shops can diagnose the specific problem based on your fail notice. Once repaired, return to any approved testing station (not necessarily the same one) to retest.

What happens if you fail twice

If your vehicle fails the retest, you have entered what Colorado calls the "two-failure" category. This does not automatically prevent registration, but it does trigger additional requirements. You may be asked to provide documentation of the repairs you attempted, or to undergo a more detailed inspection called an OBD (on-board diagnostic) test.

In some cases, the Colorado Department of Transportation may require you to take your vehicle to a state-certified repair facility for diagnosis before allowing another retest. This is meant to prevent repeated failures from the same underlying problem. The cost of this diagnostic is separate from the testing fee and varies by facility.

If your vehicle continues to fail after multiple attempts, you may lose the ability to renew your registration until the emissions problem is resolved. At that point, you would need to either repair the vehicle to pass, have it declared non-operational (which suspends registration but removes the testing requirement), or retire it.

Cost and payment options

A standard emissions test in Denver costs between $25 and $35, depending on which station you choose. Some stations charge slightly more for drive-through service or for testing diesel vehicles. The fee is due at the time of testing and most stations accept both cash and card payment.

If you fail and need to retest within 60 days at the same station, the retest is free. If you wait longer than 60 days, you will pay the full testing fee again. If you go to a different station for your retest, that station may charge the standard fee — check their policy before you go.

Some repair shops bundle emissions testing with a diagnostic service if your vehicle has failed. This is optional and separate from the required test. If you choose to use a repair shop's diagnostic, that service will cost extra and is not covered by the free retest period.

Preparing your vehicle to pass

The best preparation is regular maintenance. Keep your oil changed, your air filter clean, and your spark plugs in good condition. If your check engine light is on, have it diagnosed before you test — a mechanic can read the code for $50 to $100 and often identify the problem when ready.

Drive your vehicle normally for at least a few days before testing. A vehicle that has been sitting for weeks may fail even if it would pass after normal use. Make sure your gas cap is tight, as a loose cap can trigger a sensor that causes failure. If you have recently filled your tank with low-quality fuel, run the tank down and refill with a reputable brand before testing.

If your vehicle is older or has high mileage, consider having a pre-test inspection at a repair shop. Many shops offer this for $30 to $50 and can identify problems like a faulty oxygen sensor or catalytic converter issue before you pay for the official test. Catching these problems early can save you from a fail and the cost of a retest.

Registration and renewal after passing

Once you have a passing test result, you can complete your vehicle registration renewal with the Colorado Department of Motor Vehicles. You can renew online, by mail, or in person at a DMV office. You will need your test receipt, your current registration, proof of insurance, and payment for the registration fee (which varies by vehicle type and is separate from the testing cost).

Your new registration is valid for two years from the date of renewal. Your next emissions test will be due two years later, unless your vehicle is older than 1981, in which case you will need to test again in one year. The DMV will send you a renewal notice about 60 days before your registration expires.

If you move out of the Denver metro area to a part of Colorado that does not require emissions testing, you will not need to test again. However, if you move to another state, that state's emissions requirements will explore to your vehicle registration there.

Frequently Asked Questions

Can I test my vehicle before my registration is due?

Yes. You can test at any time, and the result is valid for 30 days. This is useful if your registration expires soon and you want to get testing done early. However, you cannot renew your registration until your current registration is within a certain window — usually 60 days before expiration — so testing too far in advance may not help you renew sooner.

What if I just bought a used car in Denver?

If the car is new to you but already registered in Colorado, you do not need a new emissions test unless the previous owner's test has expired. Check the registration card to see when the test was done. If you are registering an out-of-state vehicle in Colorado for the first time, you must pass emissions before registration is complete.

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

You must retest at the same station within 60 days to get the free retest. After 60 days, or if you choose a different station, you pay the standard testing fee again. Different stations may have slightly different fees, so it is worth calling ahead if cost is a concern.

What if my vehicle is too old or damaged to repair?

You can declare your vehicle non-operational with the Colorado DMV, which suspends registration and removes the testing requirement. This is useful if you own the vehicle but do not plan to drive it. You can reactivate it later if you repair it. Alternatively, you can retire the vehicle through a scrap or donation program.

Does Denver test motorcycles or RVs?

Motorcycles are exempt from emissions testing in Colorado. RVs and trailers have their own rules depending on their weight and registration type — check with the Colorado DMV or your local testing station to confirm whether your specific vehicle requires testing.