Motor vehicle emissions - FAQs


A vehicle may receive an alternative test for one of several reasons:

  • The required Onboard Diagnostic (OBD) inspection may not be able to be performed on a vehicle due to a communication problem that prevents the vehicle’s computer from communicating with the test equipment. Therefore, an alternative I/M 240 inspection may be performed. 
  • The required Onboard Diagnostic (OBD) inspection may not be able to be performed on a vehicle due to the vehicle’s OBD system not being ready.  While this does not necessarily mean that the vehicle has a problem, it does indicate that the vehicle’s OBD computer has not yet completed its self-tests (or become “Ready”). Therefore, an alternative IM240 inspection may be performed. 
  • A few vehicles are selected at random to receive an I/M 240 inspection instead of the Onboard Diagnostic (OBD) inspection to ensure the quality of the various inspection types. 

Collector vehicles can be passenger cars or trucks that don’t exceed 16,000 pounds empty weight and are at least 32 years old. Such vehicles are registered for a period of five years.

House Bill 13-1071 governs vehicles that qualify to register as collector vehicles, dividing them into the following categories:  

  • Category A includes model year 1975 and older vehicles. These vehicles aren’t required to obtain an emissions test, and owners aren’t required to sign the DR 2839 Collector’s Item Affidavit to renew. 
  • Category B includes model year 1976 or later vehicles that were registered prior to Sept. 1, 2009. These vehicles aren’t required to obtain a passing emissions test, and owners aren’t required to sign the DR 2839 Collector’s Item Affidavit to renew. These vehicles will remain in Category B until a change of ownership occurs. The new owner may register the vehicle as a collector vehicle, but at that time it will be placed into Category C.
  • Category C includes collector vehicles that are at least 32 years old. 
    In 2015, for example, 1983 or older vehicles qualify as collector vehicles; in 2016, the model year will be 1984; in 2017 the model year will be 1985, etc. 

    Category C is further divided into these subcategories:
    • If your vehicle is registered to an address in the Emissions Testing Program Area, you must to sign the DR 2839 Collector’s Item Affidavit and pass an emissions test to register and renew.
    • If your vehicle is at least 32 years old and is being registered outside the Emissions Testing Program Area, you aren’t required to obtain an emissions test or sign the DR 2839 Collector’s Item Affidavit.

If your vehicle is registered to an address outside the Emissions Testing Program Area but is driven at least 90 days a year to the program area for employment or school, then it falls under the requirements for emissions inspection outlined above.

  • Air Care Colorado inspects only gasoline-powered vehicles. Diesel-powered vehicles are inspected through independent diesel emissions testing facilities.
  • Light-duty vehicles with a gross vehicle weight rating (GVWR) of 14,000 pounds or less are exempt from an emissions test for four years if they are purchased brand new, and then tested after that.
  • 2003 and older vehicles are tested every year.
  • 2004 and newer vehicles are tested every two years.
  • Heavy-duty vehicles with a gross vehicle weight rating of 14,001 pounds or more are exempt from emissions testing if they are purchased brand new for their first four years, and then tested every two years until they reach their tenth year. After that, such vehicles must be tested every year.

If you're a Colorado resident temporarily living outside the state, you must complete an Application for an Affidavit of Emissions Extension (Form DR 2376). Send the completed form, an emissions test (if testing is performed in the county of temporary residence) and payment to your home county's motor vehicle office in Colorado. 

If emissions testing isn’t performed in the county of temporary residence, then you must include a Verification of Vehicle Identification Number (VIN: Form 2698) with the extension form. Any law enforcement officer can complete the VIN verification form. 

For more information about VIN verifications, visit the Colorado Department of Revenue.

Your vehicle may have failed the emissions inspection for a variety of reasons.

Here are the most common:

Note: As of January 2015, vehicles that are 8-11 years old will fail the inspection if their "Check Engine" light is turned on. These vehicles must be repaired and reinspected.

Brochure "My vehicle has failed its Emissions Test ... now what do I do?"


A properly functioning gas cap is an essential part of the vehicle's emissions control system. A missing or leaking gas cap will cause the vehicle to fail the emissions test.

We require a full retest when the vehicle fails initially for a missing or defective gas cap. Replacing the gas cap will affect the vehicle's emissions control capability and may increase its tailpipe emissions.

Brochure: "Your vehicle failed its emissions inspection because the gas cap is broken or missing.


I/M 240 stands for "Inspection and Maintenance — 240 seconds" and refers to the dynamometer (treadmill-like device) found in each lane of the emissions testing station.

Gasoline-powered vehicles that are at least 12 years old (back to model year 1982) and registered in the Automobile Inspection and Readjustment (AIR) program area require an I/M 240 test every two years. The I/M 240 test simulates emissions during a variety of driving conditions (idle, low speed and high speed) over the course of 240 seconds (4 minutes). 

More information about the I/M 240 test is available through the Air Care Colorado website


  • Inspection not required for vehicles that are seven model years old or newer.
  • Vehicles that are at least eight years old (back to model year 1982) are inspected every two years. Model year 1981 and older vehicles are inspected every year.
  • Inspection is required when a vehicle changes ownership. Change of ownership requires a new passing emissions certificate supplied by the seller at the time of the sale. This requirement doesn’t apply to vehicles that are seven model years old or newer.
  • Inspection is required for registration renewal when indicated on your registration renewal card. 
  • Inspections are required when a vehicle meets the above criteria and moves to a mailing address in the Metro Denver and north Front Range emissions inspection area.



  Back to Top 



  • Bring your vehicle and (if possible) registration renewal card with you to the emissions inspection station in order to complete the process.


  • All Air Care Colorado emissions inspection stations are open 8 a.m.-5:30 p.m. Monday-Friday, 8 a.m.-1 p.m. Saturday, and closed Sundays and all Colorado state holidays.
  • Please check the Air Care Colorado website and Twitter feed to make sure a station is open before you go there.

Wait time

  • The actual emissions inspection usually takes about 20 minutes. Wait times for the inspection vary, so please refer to Air Care Colorado's station map for current wait times at each station.


  • Emissions inspections for gasoline-powered vehicles model year 1982 and newer cost $25. 
  • Emissions tests for gasoline-powered vehicles model year 1981 and older cost $15 and are required every year.
  • AirCare Colorado inspection stations accept cash, check, Visa, MasterCard or Discover Card for payment. 
  • The cost for testing diesel-powered vehicles varies among Licensed Diesel Emission Testing Stations. Diesel inspection stations can charge up to one hour of posted labor rate.


Every vehicle built for sale in the United States since model year 1996 comes equipped with onboard diagnostics (OBD). This feature helps you quickly determine problems with your vehicle, allowing for quicker repairs and improved performance. 

Air Care Colorado tests the following components of your vehicle's OBD system: 

  • The "Check Engine" light is the primary way your vehicle's OBD system communicates with you. Inspectors check to make sure the light bulb and circuit are functioning properly.
  • Command status - Inspectors check to see if the OBD system detects any emissions-related problems, and if it can and does command the Check Engine light to turn on. 
  • Diagnostic trouble codes can describe the exact issue(s) your vehicle is experiencing.
  • "OBD: Advise" indicates the OBD system found problems. These can include communication problems, diagnostic trouble codes, issues with your Check Engine light, or something else. You should promptly seek further diagnosis and repairs to improve vehicle performance, save money, avoid failing your next emissions test, and prevent more serious problems.

Note: As of January 2015, vehicles that are 8-11 years old will fail the inspection if their "Check Engine" light is turned on. These vehicles must be repaired and reinspected.

Air Care Colorado is making OBD a more important part of its emissions testing process, giving you more test results and information on your Vehicle Inspection Report.


RapidScreen is Air Care Colorado's roadside emissions testing program. This is an alternative to standard testing at emissions testing stations, allowing you to have your vehicle's emissions screened by driving past a RapidScreen emissions testing system. 

For more information about RapidScreen, visit the Air Care Colorado website.


There are up to 11 readiness monitors in a vehicle that allow the vehicle’s Onboard Diagnostic system (computer system) to monitor for potential emissions problems. Some of these monitors run whenever the vehicle is operating while others run periodically. Once a monitor has run, it is set to “Ready” indicating that the system’s self evaluation is complete.

Part of Colorado’s OBD emissions test requires certain monitors to be set to “Ready” to ensure the system has properly performed this self evaluation. All OBD-inspected vehicles must have the Catalytic Converter, Oxygen Sensor, and Heated Oxygen Sensor (if so equipped) monitors set to “Ready” during the inspection. Vehicles model year 2000 and older can have two remaining monitors “Not Ready” while vehicles 2001 and newer can only have one unset monitor.

Specific conditions must be met while driving for the Readiness Monitors to be set to “Ready.”  Some vehicle manufacturers provide specific driving procedures to set the necessary monitors to ready.

You can report vehicles with excessive smoke to our Smoking Vehicle Hotline
 by phone at 303-692-3211
 or by email to

Please include the vehicle's license plate number and, if possible, whether it's gasoline- or diesel-powered.

This hotline is only for reporting smoking vehicles with Colorado license plates, and not out-of-state plates or temporary tags. 


For used vehicles from a dealership:

  • If the vehicle fails emissions testing, you have three business days beginning the day after you take possession of the vehicle to bring it back to the dealer for repairs/repurchase. "Business days" are defined as Monday through Saturday, with the exception of state holidays. The dealer is required by law to repair, pay a third party to repair, or repurchase the failed vehicle. The dealer will tell you which of these options it has chosen within three business days after the vehicle has been returned to the dealer.
  • If you don’t return the failed vehicle within the initial three-day period, the dealer will be relieved of responsibility to repair or repurchase the vehicle for compliance with the emissions program.
  • For more information about this situation, visit the Air Care Colorado website.


For used vehicles from a private party:

  • The seller must provide you a new Certificate of Emissions Compliance (obtained after passing the emissions test) at the time of sale.
  • For more information, contact the Colorado Department of Revenue at 303-205-5603.


If you received a “Vehicle Unable to Test” form during your inspection, it was for any of the reasons checked by the inspector. Unsafe, inaccessible, or malfunctioning equipment must be repaired before the vehicle can be inspected.

You may need an emissions inspection if your vehicle is more than 7 model years old, and;

  • A light-duty gasoline-powered vehicle, defined as weighing 8,500 pounds or less.
  • A heavy-duty vehicle defined as weighing more than 8,500 pounds.
  • A vehicle registered to a mailing address in the emissions testing program area (all of Boulder, Broomfield, Denver, Douglas and Jefferson counties, and parts of Adams, Arapahoe, Larimer and Weld counties).
  • A vehicle registered to a mailing address outside the emissions testing program area, but is driven at least 90 days a year into the program area for employment or school.
  • Also check the registration renewal card mailed to you, which will indicate one of the following:

    Due by the end of the month in which your current registration expires.

    Vehicle was "clean screened" through the RapidScreen Roadside Emissions Testing program



Some vehicles don't require an emissions inspection:

  • Vehicles that are 7 model years old and newer.
  • All-electric vehicles (hybrid-electric vehicles are inspected after 7 years).
  • Collector vehicles (model year 1975 and older).
  • Horseless carriages, street rods, farm vehicles, kit cars and motorcycles.

Contact your county clerk for more specific information.


  • Your vehicle should be on for at least 20 minutes (either through driving or idling) before taking the emissions inspection. The combination of driving to an emissions inspection station and waiting in line at the station should usually help to meet this requirement. 
  • Idling should be kept to a minimum at all other times. Idling your engine for just one minute produces as much carbon monoxide as smoking three packs of cigarettes. 
  • Find out more about Colorado's efforts to reduce vehicle idling through the Engines Off! program.



  Back to Top