What Denver County requires for emissions testing

Denver County requires emissions testing for most vehicles registered in the county, with some exceptions. Your vehicle needs to pass an OBD emissions test (on-board diagnostic test) every two years if it was built in 1981 or later. The test checks whether your vehicle's emissions control system is working properly by reading data from your engine's computer.

You must complete emissions testing before you renew your vehicle registration with the Colorado Department of Revenue. If your registration expires and you have not passed the test, you cannot legally renew. The test itself takes about 10 to 15 minutes at a certified testing station.

Diesel vehicles, motorcycles, and vehicles older than 1981 are exempt from Denver County emissions testing. Vehicles registered outside Denver County but driven there regularly do not need to pass Denver County's test — they follow the rules of their home county.

Key Takeaways

  • Denver County requires OBD emissions testing every two years for vehicles built in 1981 or later before you can renew registration.
  • The test costs between $20 and $40 at a certified testing station and takes 10 to 15 minutes.
  • You can find certified testing stations through the Colorado Department of Revenue website or by calling 303-205-5600.
  • If your vehicle fails, you have 60 days to repair it and retest at no additional charge at the same station.
  • Diesel vehicles, motorcycles, and pre-1981 vehicles do not need emissions testing in Denver County.

Finding a testing station and scheduling

The Colorado Department of Revenue maintains a list of certified emissions testing stations in Denver County on its website. You can search by ZIP code or station name. Most stations are independent repair shops, not dealerships, and many offer walk-in testing without an appointment.

Call ahead if you want to confirm hours or ask about wait times. Some stations get busy during the last month before registration important date, so testing earlier in your renewal window usually means shorter waits. You will need your vehicle's registration and proof of insurance to bring with you.

What happens if your vehicle fails the test

If your vehicle fails the emissions test, the testing station will give you a printed report showing which emissions systems did not pass. You have 60 days from the test date to have the vehicle repaired and retested. The retest is free at the same station where you failed, even if you take the vehicle elsewhere for repairs.

Common reasons for failure include a faulty oxygen sensor, a loose or missing gas cap, or problems with the catalytic converter. A mechanic can read the diagnostic codes from your vehicle's computer to pinpoint the issue. Repair costs vary widely depending on what needs fixing — a gas cap might cost $15, while a catalytic converter can cost several hundred dollars.

If you cannot afford repairs, some nonprofits in Denver County offer low-cost repair information for low-income vehicle owners. Contact the Colorado Department of Revenue at 303-205-5600 to ask about programs in your area.

Timing your test before registration renewal

You can take the emissions test up to 60 days before your registration expires. The Colorado Department of Revenue will not process your registration renewal without a passing emissions test result on file. Testing early gives you time to repair and retest if you fail, rather than scrambling in the final days before your registration lapses.

Your registration renewal notice will show your expiration date. Plan to test at least 30 days before that date so you have a buffer for repairs if needed. If your registration has already expired, you can still test and renew, but you cannot legally drive the vehicle until the renewal is complete.

Cost and payment methods

Emissions testing in Denver County costs between $20 and $40 per test, depending on the station. Most testing stations accept cash, debit cards, and credit cards. The price is set by individual stations, so you can call ahead to compare if cost is a concern.

The retest after a failure is free at the same station. If you take your vehicle to a different station for the retest, you will pay the full testing fee again. Some stations offer discounts for seniors or low-income residents — ask when you call to schedule.

What the OBD test actually checks

The OBD test reads data from your vehicle's onboard diagnostic computer without any physical probes or tailpipe sampling. The technician plugs a scanner into a port under your steering wheel, usually on the left side of the dashboard. The scanner retrieves information about your emissions control systems — oxygen sensors, catalytic converter, fuel system, and exhaust gas recirculation system.

The test passes if your emissions systems are functioning and no fault codes are stored in the computer. It does not measure the actual pollution coming out of your tailpipe. A vehicle can pass the OBD test and still emit high levels of pollutants if the test does not detect a malfunction, though this is rare.

Vehicles that do not need testing in Denver County

Diesel-powered vehicles are exempt from Denver County emissions testing, even if they are newer than 1981. Motorcycles and mopeds do not require testing. Vehicles manufactured before 1981 are also exempt because they do not have onboard diagnostic systems.

If you own a vehicle that is exempt, you still need to renew your registration normally — you just do not need to submit an emissions test result. Your registration renewal will process without one.

Frequently Asked Questions

Can I test my vehicle in a different county and use that result in Denver County?

No. Denver County requires testing at a station certified by the Colorado Department of Revenue specifically for Denver County. If you move to Denver County or register a vehicle there, you must test at a Denver County station. Tests from other counties do not transfer.

What if I just moved to Denver County — do I need to test when ready?

You need to test before you renew your registration with the Colorado Department of Revenue. If your registration does not expire for several months, you can wait until closer to that date. If it expires soon, you should test within the next few weeks to leave time for repairs if you fail.

Do I have to test if I only drive through Denver County occasionally?

If your vehicle is registered in Denver County, yes — you must test every two years before renewal, regardless of how often you drive. If your vehicle is registered in a different county, you follow that county's rules, not Denver County's, even if you drive there regularly.

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

Some vehicles with severe electrical or engine problems cannot be tested because the diagnostic scanner cannot communicate with the vehicle's computer. The station will give you a written statement explaining why. Take this to the Colorado Department of Revenue — you may be able to renew your registration conditionally while you repair the vehicle.

How long does a passing test result stay valid?

A passing test result is valid for two years from the test date. You can renew your registration anytime during those two years using that result. After two years, you must test again before the next renewal.