What Denver's emission test measures and who has to take it

Denver requires an emission test every two years for most vehicles registered in the metro area. The test measures what comes out of your tailpipe: nitrogen oxides, particulate matter, carbon monoxide, and hydrocarbons. A machine plugs into your vehicle's onboard diagnostic port (usually under the steering wheel) and reads the data your car's computer has already collected. The test takes about 10 minutes and costs between $25 and $35 depending on which testing station you visit.

You need a test if you own a vehicle registered in Denver, Adams, Arapahoe, Boulder, Broomfield, Douglas, El Paso, Elbert, Jefferson, Larimer, or Weld County. Vehicles older than model year 1982 are exempt. Diesel trucks and motorcycles follow different rules. If your vehicle has a check engine light on, the test station will fail you on the spot — you cannot pass until that light is off and the underlying problem is fixed.

Key Takeaways

  • Denver emission tests happen every two years and measure tailpipe emissions through your vehicle's onboard computer, taking about 10 minutes at a certified station.
  • You must schedule your test before your registration expires, and the test result is valid for two years from the date you take it.
  • A check engine light will cause an automatic failure, so have that diagnosed and repaired before you arrive at the testing station.
  • If you fail, you have 60 days to fix the problem and retest at no additional charge at the same station.
  • Vehicles registered outside the Denver metro area do not need emission testing, even if you drive through Denver regularly.

When your test is due and how to schedule it

Your emission test must be completed before your vehicle registration expires. The Colorado Division of Motor Vehicles sends a renewal notice in the mail about 30 days before expiration, and that notice tells you whether your vehicle needs a test. You can also check your registration status online at the DMV website by entering your license plate number.

Testing stations are scattered across the metro area — you do not have to go to a specific location. Search for "emission testing near me" or visit the Colorado Department of Public Health and Environment website, which lists all certified stations by county. Most stations operate Monday through Friday during business hours, and some open Saturday mornings. You can call ahead to ask about wait times, but you do not need an appointment at most locations. Walk-ins are common, though you may wait 30 minutes to an hour during peak times (late morning and early afternoon).

What happens if you fail the test

A failure means your vehicle's emissions exceed Colorado limits. The testing station prints a report showing which pollutants were over the limit and by how much. You have 60 days from the test date to have the vehicle repaired and retested at the same station. The retest is free — you only pay the initial test fee.

Common reasons for failure include a faulty oxygen sensor, a clogged fuel injector, a worn spark plug, or a problem with the catalytic converter. A mechanic can read the diagnostic codes from your vehicle's computer to narrow down the cause. If the repair is expensive, you may be able to get a waiver. Colorado offers a repair cost waiver if the repair would cost more than $500 and you have already failed twice in a row. Contact the testing station for waiver forms and instructions.

Documents and fees you need to bring

Bring your vehicle registration or a photo ID and proof of residency. The testing station needs to confirm you are registered in the testing area. You also need to know your vehicle identification number (VIN), which is on your registration or visible on the dashboard at the base of the windshield on the driver's side. Have your keys ready so the technician can start the vehicle.

The test fee ranges from $25 to $35 depending on the station. Most stations accept cash, debit, and credit cards. If you fail and need to retest, bring the same documents and your original test report. The retest is free, but you still need to pay if you take a new initial test at a different station.

How to prepare your vehicle before testing

Drive your vehicle for at least 10 minutes before arriving at the testing station. The engine needs to be warm for the test to run correctly. If your check engine light is on, do not go to the station — have a mechanic diagnose the problem first. A lit check engine light is an automatic failure.

Make sure your gas cap is tight and not cracked. A loose or damaged cap can trigger a check engine light. If your vehicle has not been driven in several days, take it for a longer drive (20 to 30 minutes) before testing to clear out any stale fuel and let the engine computer run its self-diagnostic cycle. This step is especially important if you have just had work done on the fuel system or ignition.

What to do if you move or sell your vehicle

If you move out of the Denver metro testing area, you no longer need emission tests. When you register your vehicle in a new county outside the testing area, the DMV will stop requiring the test. If you sell your vehicle to someone in the testing area, the new owner becomes responsible for the next test. The test result does not transfer with the vehicle.

If you move within the testing area, your test requirement stays the same — you still need a test every two years based on your registration renewal date. The testing area includes 11 counties, so moving from one county to another within that region does not change your obligation.

Frequently Asked Questions

Can I test my vehicle before my registration expires?

Yes. You can take the test up to 60 days before your registration expires. The test result is valid for two years from the date you take it, so testing early gives you flexibility if you need to schedule repairs.

What if I fail and cannot afford the repair?

You may be able to get a repair cost waiver if the repair exceeds $500 and you have failed twice in a row. Ask the testing station for a waiver process. Some nonprofits and county programs also offer repair information for low-income vehicle owners, though funding and may be able to access vary by county.

Do I need to test if I only drive through Denver occasionally?

No. You only need to test if your vehicle is registered in one of the 11 counties in the Denver metro area. Where you drive does not matter — registration location determines the requirement.

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

Some vehicles cannot complete the test — for example, if the onboard diagnostic port is damaged or if the vehicle is too new or too old for the equipment. Ask the station for a written explanation. You may need to contact the Colorado Department of Public Health and Environment for guidance on next steps.

How long does a retest take if I fail?

A retest takes the same 10 minutes as an initial test. You have 60 days from your original test date to complete the retest. Return to the same station where you failed, bring your original test report, and the retest fee is waived.