What Denver requires and who has to test

Denver requires emissions testing for most vehicles registered in the city, though the exact rules depend on your vehicle's age, fuel type, and how often you drive. Gasoline vehicles from model year 1981 and newer must test. Diesel vehicles from 1997 and newer must test. Electric vehicles and vehicles from 1980 and earlier are exempt. If you register your vehicle in Denver County, you will need to pass an emissions test before you can renew your registration — the test is not separate from registration, it is part of the process.

The Colorado Department of Transportation (CDOT) oversees the emissions program statewide, but Denver operates its own testing network. You cannot test in another Colorado county and use that result for a Denver registration. The test must happen at a Denver-area testing facility, and you must complete it before your current registration expires.

Vehicles that are brand new to you (newly purchased or newly moved to Denver) have a grace period. You have until your first registration renewal to complete your first test. After that, testing is required every two years for most vehicles, though some older or higher-emission vehicles may need to test annually — the testing facility will tell you which category your vehicle falls into when you arrive.

Key Takeaways

  • Gasoline vehicles from 1981 onward and diesel vehicles from 1997 onward must test in Denver; electric vehicles and pre-1981 vehicles do not.
  • You must test at a Denver-area facility before your registration renewal date, and the test result is required to complete registration.
  • Testing happens every two years for most vehicles, though some older vehicles test annually — the facility will confirm your schedule when you arrive.
  • The test itself takes about 10 minutes and costs between $20 and $30, depending on the testing facility.
  • If your vehicle fails, you have 60 days to repair it and retest at no additional charge at the same facility.

Finding a testing location and scheduling

Denver has multiple emissions testing stations run by private contractors under CDOT oversight. The official CDOT website lists all active testing locations, their hours, and whether they accept walk-ins or require appointments. Some facilities accept both; others are appointment-only. Call ahead or check the facility's website before you go, because hours vary by location and some close for lunch or maintenance.

Testing stations are spread across Denver and surrounding areas — you are not required to test at a specific location, only at one that is authorized for Denver County. Popular facilities often have wait times during peak hours (typically late afternoon and weekends), so testing early in the day or mid-week usually means shorter waits. If your registration expires soon, do not wait until the last week; testing facilities can become backed up, and you cannot legally drive with an expired registration.

You do not need an appointment at many locations, but calling first saves time. Have your vehicle's VIN (vehicle identification number) and current registration handy when you call or arrive. Some facilities let you schedule online; others require a phone call.

What happens during the test

The emissions test itself is a straightforward process that takes about 10 minutes. You drive into a bay, a technician connects a probe to your vehicle's tailpipe, and the equipment measures what comes out. For most vehicles, this is a tailpipe test. For 1996 and newer vehicles, the technician also plugs a scanner into your vehicle's onboard diagnostic port (usually located under the steering wheel on the driver's side) to read emissions data from your vehicle's computer.

Your vehicle must be warmed up before testing — if you arrive and the engine is cold, the technician may ask you to drive around the parking lot for a few minutes first. Bring your keys and be prepared to sit in the vehicle during the test. The technician will tell you whether you passed or failed before you leave. If you pass, your result is sent electronically to the Colorado Division of Motor Vehicles, and you can proceed with registration renewal when ready.

The test costs between $20 and $30 depending on the facility. Most accept cash, card, or both. Ask about payment methods when you call to schedule or arrive.

What to do if your vehicle fails

If your vehicle fails the emissions test, you have 60 days to repair it and retest at no additional charge at the same facility where you failed. The technician will give you a printed report showing which emissions standards your vehicle did not meet. This report is useful to show a mechanic, though it does not specify what repair is needed — that is the mechanic's job to diagnose.

Common reasons for failure include a faulty oxygen sensor, a malfunctioning catalytic converter, a loose or missing gas cap, or an engine running too rich (burning too much fuel). Some repairs are inexpensive (a gas cap replacement might cost $15 to $30); others are costly (catalytic converter replacement can run $800 to $2,500 depending on the vehicle). Get a repair estimate before committing, and ask your mechanic whether the specific repair will address the emissions issue your vehicle failed on.

After repairs, return to the same testing facility within 60 days and retest. You do not pay again. If you pass the retest, your result is sent to the DMV and you can complete registration. If you fail again, you have another 60 days to repair and retest. If you cannot repair the vehicle within the 60-day window, you can request a waiver from the Colorado Division of Motor Vehicles, though waivers are granted only in specific circumstances (such as if repairs cost more than a certain percentage of the vehicle's value).

Registering after you pass the test

Once your vehicle passes the emissions test, the result is transmitted electronically to the Colorado Division of Motor Vehicles. You do not need to carry the test result with you or submit it separately. You can renew your registration online through the DMV website, by mail, or in person at a DMV office or authorized county clerk's office. The system will show that your emissions test is complete, and you will not be able to proceed with registration until the test result is in the system.

Registration renewal can happen up to 60 days before your current registration expires. If you test early, you can renew early. If you wait until the last few days, you risk running out of time if the testing facility is busy or if your vehicle fails and needs repairs.

Special situations and exemptions

New residents moving to Denver from out of state have until their first registration renewal to complete an emissions test. If you move to Denver mid-year, your first test is due when your out-of-state registration would have renewed. Vehicles registered as antiques or classics (typically 25 years old or older, depending on the model year) are exempt from testing, though you must register them as antique vehicles.

Vehicles with a waiver from the Colorado Division of Motor Vehicles are exempt from testing for the duration of the waiver. Waivers are issued when a vehicle has failed testing twice and the owner can demonstrate that repairs would cost more than a set percentage of the vehicle's value (currently 7 percent). To request a waiver, contact the Colorado Division of Motor Vehicles directly with documentation of your failed tests and repair estimates.

Hybrid vehicles and vehicles with alternative fuel systems (such as compressed natural gas) follow the same testing rules as gasoline vehicles, though the testing procedure may differ slightly. Tell the testing facility what type of vehicle you have when you arrive, and they will direct you to the correct bay.

Planning ahead for registration renewal

Mark your registration expiration date on a calendar and plan to test at least two weeks before that date. This gives you time to test, pass, and complete registration without rushing. If your vehicle is older or has had emissions issues in the past, test even earlier — three to four weeks before expiration — to allow time for repairs if needed.

Keep your emissions test results and any repair receipts in your vehicle's file. If you ever dispute a test result or need to request a waiver, these documents are useful. The testing facility keeps records, but having your own copy is helpful.

If you are unsure whether your vehicle must test, call a Denver testing facility or check the CDOT website. Providing your vehicle's VIN and model year will get you a quick answer about whether testing is required and how often.

Frequently Asked Questions

Can I test in a different Colorado county and use that result for Denver registration?

No. Denver requires testing at a Denver-area facility. Results from other counties do not transfer. You must test in Denver County to renew a Denver registration.

What if I cannot afford the repair after my vehicle fails?

You can request a waiver from the Colorado Division of Motor Vehicles if repairs cost more than 7 percent of your vehicle's value. You will need documentation of the failed test and repair estimates. Contact the DMV directly to start the waiver process. If a waiver is denied, you have 60 days to repair and retest.

Do I have to test if I work from home and rarely drive?

Yes, if your vehicle is registered in Denver County, it must test before registration renewal, regardless of how often you drive. The testing requirement is tied to registration, not to actual driving.

What happens if I let my registration expire without testing?

Driving with an expired registration is illegal in Colorado. You cannot legally operate the vehicle on public roads. If you are pulled over, you face a fine. Complete the emissions test and renew your registration before the expiration date.

How long does the emissions test result stay valid?

An emissions test result is valid for two years from the test date for most vehicles, though some older vehicles require annual testing. When you pass, the facility will tell you when your next test is due. The result is tied to your registration renewal cycle.