What Colorado requires from your vehicle

Colorado requires emissions testing for most vehicles registered in the state, but the rules depend on where you live and what you drive. The state divides the requirement into two zones: the Denver Metro area (which includes Denver, Boulder, and surrounding counties) and the rest of Colorado. Vehicles in the Denver Metro area face stricter standards and must test every two years. Vehicles outside that zone are tested less frequently or not at all, depending on their model year and fuel type.

The Denver Metro area includes Adams, Arapahoe, Boulder, Broomfield, Clear Creek, Denver, Douglas, El Paso, Gilpin, Jefferson, Larimer, Park, and Weld counties. If your vehicle is registered in any of these counties, you will need to pass an emissions test before you can renew your registration. If you live elsewhere in Colorado, your vehicle may not need testing at all, or testing may be required only once every five years.

Diesel vehicles, motorcycles, and vehicles older than 1975 are generally exempt from testing. Vehicles registered as antiques or classics may also be exempt. The Colorado Department of Transportation (CDOT) and the Air Quality Control Commission set these rules, and they can change based on air quality conditions in the Denver Metro area.

Key Takeaways

  • Vehicles registered in the Denver Metro area must pass an emissions test every two years before registration renewal, while vehicles outside that zone may test less often or not at all.
  • The test measures tailpipe emissions of nitrogen oxides, particulate matter, and other pollutants; a vehicle that fails must be repaired before it can be registered.
  • Testing costs between $20 and $30 per vehicle in Colorado, and you can find testing stations through the Colorado Department of Public Health and Environment website.
  • If your vehicle fails, you have options including repair, a waiver for vehicles over 15 years old, or a temporary registration extension while repairs are underway.
  • Vehicles registered outside the Denver Metro area face different rules based on model year, and many older or alternative-fuel vehicles are exempt entirely.

How the emissions test works and what it measures

An emissions test takes about 10 to 15 minutes and measures what comes out of your tailpipe. The test checks for nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), and particulate matter. For most gasoline vehicles, the test is a two-speed idle test: the vehicle idles at a low speed, then the technician revs the engine to a higher speed, and the machine records the emissions at each point. The vehicle must stay within Colorado's limits for each pollutant to pass.

Diesel vehicles and some newer gasoline vehicles use a different protocol. Diesel vehicles may undergo a snap acceleration test, where the engine is revved quickly and emissions are measured during that burst. Newer vehicles (typically 2000 and later) may be tested using an on-board diagnostic (OBD) scan, which reads the vehicle's computer for emissions-related fault codes. If the vehicle has a check engine light or a fault code related to emissions, it will fail the OBD test.

You cannot pass an emissions test if your vehicle has a check engine light on, even if the light is for an unrelated issue. The test station will not perform the test until the light is off. You can have the code read at most auto parts stores for free, or at a repair shop, to find out what triggered it.

Who must test and who is exempt

In the Denver Metro area, all gasoline and diesel vehicles registered there must test every two years, with a few exceptions. Vehicles registered as antiques or classics (usually 25 years or older, depending on the county) are exempt. Motorcycles are exempt. Vehicles powered entirely by electricity or hydrogen fuel cells are exempt. Vehicles that have been registered for less than 30 days are exempt from the current test cycle but will need to test in the next cycle.

Outside the Denver Metro area, the rules are less strict. Vehicles registered in rural Colorado counties may not need to test at all, or may test only once every five years. Vehicles model year 1981 and older are exempt statewide. Diesel vehicles registered outside the Denver Metro area are generally exempt. Check your vehicle registration notice or contact your county clerk to find out whether your vehicle must test.

If you move to Colorado from another state and register your vehicle here, you must test before your registration is renewed, even if you just moved. The test requirement applies to your vehicle's registration location, not where you lived before.

Finding a testing station and scheduling

Colorado has about 150 emissions testing stations across the state, run by private businesses under contract with the state. You can find a station near you through the Colorado Department of Public Health and Environment (CDPHE) website or by searching "emissions testing near me" online. Most stations are independent repair shops, tire shops, or dedicated testing facilities. You do not have to go to a dealership.

Testing stations are open year-round, but they are busiest in the weeks before registration renewal important date. If your registration expires in a specific month, you can test anytime in the two months before that month. For example, if your registration expires in June, you can test in April or May. Testing early can save you from a rush.

Most testing stations accept walk-ins, but some require appointments. Call ahead or check the station's website to see if you need to book a time. Bring your vehicle registration and a valid ID. The test takes 10 to 15 minutes, and you will receive a pass or fail notice on the spot. If you pass, the result is sent electronically to the Colorado Division of Motor Vehicles (DMV), and you can renew your registration when ready.

What happens if your vehicle fails

If your vehicle fails the emissions test, you cannot renew your registration until you fix the problem and retest. You have several options. The first is to repair the vehicle and return to the same testing station or a different one for a retest. Repairs can range from $50 (for something like a loose gas cap) to several hundred dollars (for a catalytic converter or oxygen sensor). Many repair shops can diagnose the problem based on the emissions test results.

If your vehicle is 15 years old or older, you may be may be able to access for a waiver. A waiver allows you to register the vehicle without passing the test, but only if you have already spent at least $500 on repairs in the past two years and the vehicle still fails. To get a waiver, you must provide receipts from a repair shop showing the work done. The waiver is not automatic; you must request it from your county clerk or through the DMV.

If you need time to repair the vehicle, you can request a temporary registration extension (usually 30 to 60 days) from your county clerk. This gives you time to get the repairs done and retest without driving an unregistered vehicle. You will need to show proof that you have taken the vehicle to a repair shop or scheduled an appointment.

Costs and what to expect at the station

The emissions test itself costs between $20 and $30 in Colorado, depending on the testing station and the type of vehicle. This fee goes to the testing station, not to the state. Some stations charge slightly more for diesel vehicles or for vehicles that require an OBD scan. The fee is separate from your registration renewal fee.

If your vehicle fails and you need repairs, costs depend on what is wrong. Common repairs include replacing an oxygen sensor ($100 to $300), fixing a loose or faulty gas cap ($10 to $50), replacing a catalytic converter ($400 to $1,200), or addressing a check engine light code ($50 to $500 in labor, depending on the problem). Some repair shops offer free diagnostic scans to identify the issue before you commit to repairs.

If you use a repair shop to fix the vehicle before retesting, ask whether they will retest for free or at a discount. Some shops offer free retests if they did the repair work. You can also retest at a different station if you prefer. There is no penalty for retesting at a new location.

Understanding Colorado's air quality zones and future changes

Colorado's emissions testing rules are tied to air quality in the Denver Metro area. When air quality worsens, the state may tighten testing standards or expand the testing zone to include more counties. When air quality improves, the state may relax the rules. The Air Quality Control Commission reviews these standards every few years and can make changes based on monitoring data.

In recent years, the Denver Metro area has struggled with ozone pollution in summer months, which is why testing standards remain strict there. Rural areas of Colorado generally have better air quality and face fewer testing requirements. If you move from a rural county to the Denver Metro area, your vehicle will need to test every two years from that point forward.

The state also offers incentives for vehicle owners to retire older, high-emission vehicles or to switch to electric or hybrid vehicles. These programs are separate from the testing requirement, but they can help offset the cost of buying a cleaner vehicle if yours fails repeatedly.

Frequently Asked Questions

Can I renew my registration if my vehicle fails the emissions test?

No. You must pass the test or receive a waiver before the DMV will renew your registration. If your registration expires before you pass, you cannot legally drive the vehicle. Request a temporary extension from your county clerk if you need time for repairs.

What does a check engine light mean for the emissions test?

A check engine light means the vehicle's computer has detected a fault, often related to emissions. The testing station will not perform the test until the light is off. Have the code read at an auto parts store or repair shop to find out what triggered it, then have it fixed.

Do I have to test at the same station where I tested before?

No. You can test at any Colorado emissions testing station. If you failed at one station and had repairs done, you can retest at a different station if you prefer. The results are reported to the DMV regardless of which station you use.

What if I just bought a used vehicle in Colorado?

If you register it in Colorado, it must pass an emissions test before your first registration renewal, unless it is exempt. You have until your registration expires to pass the test. If you buy a vehicle late in the registration cycle, you may have only a few weeks to test.

Are electric vehicles exempt from testing?

Yes. Vehicles powered entirely by electricity or hydrogen fuel cells are exempt from emissions testing in Colorado. Hybrid vehicles (gas and electric) are not exempt and must test like gasoline vehicles.