Motor vehicle emissions


Gasoline-powered vehicle inspections 


General emissions inspection requirements and information

Check the registration renewal postcard that your county clerk mails to you about a month before your vehicle’s registration renewal is due.

  • If “EMISSIONS TEST REQUIRED” appears on the card, then you'll need to take your vehicle to an Air Care Colorado inspection station.
  • New vehicles are exempt from inspection for the first seven model years. A 2011 vehicle, for example, doesn't need an inspection until 2018.
  • Vehicles 8 through 11 years old will be inspected using onboard diagnostics (OBD).
    • If the “Check Engine” light is turned on, these vehicles will fail the inspection and need repairs.
    • Making repairs improves vehicle performance, extends vehicle life and saves money.
    • Learn more at EPA or National OBD Clearinghouse.
  • Vehicles manufactured beginning in 1982 that are at least 12 years old will be inspected using the  “I/M 240” dynamometer (treadmill) test.

    • In 2016, this requirement applies to model year 1982 through 2005 vehicles and so on.
    • A check engine light on a vehicle at least 12 years old may still pass if the I/M 240 test can be run and the car can pass the test. An advisory may be issued. 
  • Vehicles manufactured in 1981 and older will be inspected using a two-speed idle test.

  • Hybrid vehicles 8 years and older will be inspected using onboard diagnostics (OBD). As with all vehicles inspected, hybrids will also have their gas caps checked, and no visible smoke is allowed.

  • ​Most inspection stations now have at least two lanes dedicated to inspecting all-wheel-drive vehicles to accommodate the large number of these vehicles.

  • RapidScreen roadside tests remain an important part of the program, allowing exceptionally clean vehicles to skip a trip to an inspection station. 

    • Owners of eligible vehicles will see “PASSED ROADSIDE EMISSIONS” on their registration renewal cards, and they won't need to go to an inspection station.

    • Current RapidScreen locations are posted on the Air Care Colorado website.

  • Air Care Colorado inspection stations accept cash, checks, Visa, MasterCard and Discover.
  • Diesel-powered vehicles are inspected through a different program.

For more information, contact Air Care Colorado: 303-456-7090


Metro Denver and North Front Range emissions inspection

County requirements

  • You must have an emissions inspection done on any gasoline-powered vehicle when you register, renew registration for, or sell the vehicle within the Automobile Inspection and Readjustment (AIR) program area. The program area covers all or parts of the following counties:
    • Adams (west of Kiowa Creek)
    • Arapahoe (west of Kiowa Creek)
    • Boulder
    • Broomfield
    • Denver
    • Douglas
    • Jefferson
    • Larimer (Fort Collins, Loveland, Windsor, and surrounding mountain areas).
    • Weld (Greeley, Windsor and the I-25 corridor).
  • Vehicles registered to an address outside the program area but driven regularly into the program area (e.g., for work or school) must be inspected.

Inspections for 1982 and newer vehicles

  • An enhanced inspection is required every two years for 1982 and newer gasoline-powered light duty vehicles (i.e. paasenger cars and light trucks under 8,501 pounds GVWR).
  • Many vehicles can pass inspection by driving past the RapidScreen roadside unit found throughout the program area. 
  • Vehicle owners learn if they need an inspection (e.g., "EMISSIONS TEST REQUIRED") through the registration renewal cards they they get from their county clerks.
  • Newer vehicles are exempt from inspection to the original owner for the first seven years. A 2010 vehicle, for example, won't need a emissions inspection until 2017.
  • Vehicles that are 8 through 11 years old get a test of their onboard diagnostic (OBD) computer systems.
  • AS OF JANUARY 2015: vehicles in this age range with their "Check Engine" light turned on will fail the inspection. They must be repaired and reinspected in order to pass.
  • AS OF JANUARY 2015: Hybrid and plug-in hybrid vehicles that are 8 years and older must have a test of their OBD computer systems. If these vehicles have their "Check Engine" light on, they will fail the inspection and must be repaired and reinspected in order to pass. 
  • Fully electric powered vehicles (i.e., with no gas tank or tailpipe emissions) remain exempt from inspection. 
  • Vehicles that are 12 years and older will have their emissions tested on a dynamometer (a treadmill-like device that provides real-time emissions data). Hybrid vehicles aren't placed on the dynamometer.
  • The inspection can be done at any Air Care Colorado inspection stations
  • Collector vehicles are subject to different emissions requirements.
  • See the frequently requested information page or the Air Care Colorado website for additional emissions inspections information. 

Inspections for 1981 and older vehicles

A two-speed idle test is required every year for 1981 and older light-duty vehicles and all heavy truck. This test can be done at Air Care Colorado stations or independent licensed test stations.

Enhanced inspection expanded to North Front Range 

The Enhanced Vehicle Emissions inspection was expanded in 2010 to parts of Larimer and Weld counties to control ground-level ozone. 


RapidScreen Roadside Emissions Testing Program

To reduce the number of vehicles requiring a traditional emissions inspection, the RapidScreen roadside emissions testing program was established for metro Denver and northern Front Range. The RapidScreen program measures emissions and records license plate numbers as vehicles drive past roadside monitors. 

You can skip a trip to the Emissions Inspection Station if your notified by mail that your vehicle passed RapidScreen. 



On Board Diagnostics (OBD) and being READY for an inspection

Every vehicle built for sale in the USA since model year 1996 has On Board Diagnostics (OBD). This feature helps find potential problems with the vehicle, leading to quicker repairs, improved performance, and better air quality. 

Make sure your vehicle is ready for the next inspection.

If you received an "Incomplete Inspection Report," it may be because:

  • Your OBD system had problems communicating with the station's test equipment

  • Your OBD system is "Not Ready" for an inspection. 

OBD monitors must be set to "Ready" before getting an inspection. Readiness monitors are set by a procedure known as a Drive Cycle. Many vehicle manufacturers include Drive Cycle procedures in the owner's manuals. In many cases, a few days of the normal city and highway driving will complete the Drive Cycle and set the required monitors to "Ready." Many repair technicians can verify that the required readiness monitors are set to "Ready." 

The following list gives manufacturer-specific information for Drive Cycle procedures (NOTE: You must follow post speed limits, traffic laws, and road conditions when performing these Drive Cycle procedures):

These procedures are not guaranteed to work for all vehicles. Please contact your vehicle maker for specific drive-cycle and other information about your vehicle. 

CDPHE operates several Emissions Technical Centers that can also provide assistance: Phone - 1-888-861-2646 

Performing a readiness monitor check

Some vehicle manufactures show you how to see if the On Board Diagnostics (OBD) system is ready for an emissions inspection. 

The following manufacturer-specific procedures can help determine if the required monitors are set to "Ready." NOTE: This list is not all-inclusive, and may not work for all vehicle from that manufacturer. 

Some newer Ford, Lincoln, and Mercury vehicles:

Turn the ignition switch to the "ON" position for 15 seconds without starting the engine:

  • If the "Check Engine" light blinks eight (8) times, then the monitors are "Not Ready"
  • If the "Check Engine" light stays on solid, then the monitors are "Ready"

Some Jeep, Chrysler, and Dodge vehicles:

Turn the ignitions switch to the "ON" position without starting the engine. The "Check Engine" light will turn on, and one of two things will happen about 15 seconds later:

  • If the "Check Engine" light blinks for about ten (10) seconds and then stays on solid the monitors are "Not Ready"
  • If the "Check Engine" light does not blink at all and stay on solid, the monitors are "Ready"

Some Honda and Acura vehicles:

Turn the ignition switch to the "ON" position without starting the engine. The "Check Engine" light will come on for about 20 seconds, and then one of the following things will happen:

  • If the "Check Engine" light blinks five (5) times, then the monitors are "Not Ready"
  • If the "Check Engine" light goes off, then the monitors are "Ready"

Vehicles with known Readiness Monitor issues:

If your vehicle is listed below, please take it to the manufacturer for the required service. This table lists specific vehicle makes and models with known readiness monitor issues. 

1996 Chrysler Cirrus, Sebring, Concord, LHS All monitors reset to incomplete upon every ignition key-off. TSB #18-005-01
1996 Dodge Stratus, Intrepid, Neon, Avenger All monitors reset to incomplete upon every ignition key-off. TSB #18-005-01
1996 Eagle Vision Non-turbo, Talon Non-turbo All monitors reset to incomplete upon every ignition key-off. TSB #18-005-01
1996 Plymouth Breeze, Neon All monitors reset to incomplete upon every ignition key-off. TSB #18-005-01
2003 Ford Focus Monitors may be difficult to complete TSB #06-7-5
2003 Hyundai Tiburon Will not communicate with OBD test equipment.  TSB #03-01-003-01
2005, 2006 Jeep Wrangler Oxygen sensor heater readiness remains incomplete. TSB #25-001-07
2007 Lexus RX400 Monitors may be difficult to complete. OBD Drivability Re-flash
2007 Toyota Highlander Monitors may be difficult to complete. OBD Drivability Re-flash
2010 Dodge Charger 3.5L, Challenger 3.5L Evaporative Leak Detection Monitor may not set to ready. TSB #18-008-10 Rev. A
2010 Chrysler 300 3.5L Evaporative Leak Detection Monitor may not set to ready.  TSB #18-008-10 Rev. A
2010, 2011 Jeep Wrangler 3.8L Downstream oxygen sensor monitor may not set to ready.  TSB #18-027-10


CDPHE operates six Emissions Technical Centers which can also check readiness Monitors: 888-861-2646.


Administration of the Automobile Inspection and Readjustment (AIR) Program

The Automobile Inspection and Readjustment (AIR) Program's purpose is to reduce motor-vehicle-related pollution through the inspection and emissions-related repair of gasoline-powered motor vehicles.


  • The program is administered jointly by our Air Pollution Control Division and the Colorado Department of Revenue.
    • The Air Pollution Control Division certifies the program, including testing procedures and equipment.
    • It works with the Air Quality Control Commission, the Regional Air Quality Council, the state Legislature, local governments, the U.S. Environmental Protection Agency (EPA) and others in assessing the effectiveness of the program and in determining program modifications.
  • The Department of Revenue administers the day-to-day operations, including:
    • Licensing of inspectors and test facilities.
    • Conducting field audits.
    • Investigating complaints.
    • Processing waivers.
    • Collecting revenues.
    • Working with county governments that issue vehicle registrations.

More information

Automobile Inspection and Readjustment Program Annual Reports:

Air Care Colorado 
Information on emissions testing, including station locations, fees, testing tips and what to do if your car fails.

Colorado Department of Revenue 
Answers to frequently asked questions about emissions testing.

Fuel economy website
From the EPA listing gas mileage, greenhouse gas emissions, air pollution ratings and safety information for new and used cars and trucks.



Please send questions/comments to  



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Diesel-powered vehicle inspections



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Emissions technical centers 

CDPHE operates emissions technical centers throughout the Denver Metro and North Front Range areas. These are multifunction facilities that conduct a variety of customer service and field activities to help vehicle owners and the repair industry meet emission requirements.

Emissions technical centers are especially helpful if your vehicle has already failed multiple emissions inspections. Their technicians are experts in identifying emissions-related problems, but they do not make any repairs.

Emissions technical centers serve motorists, independent and franchised auto dealers, automotive repair technicians, diesel fleet owners and operators, petroleum marketers, alternative-fuel vehicle converters and consumers, and the Colorado Department of Revenue.

Emissions technical centers also provide training and certification for repair technicians and emissions inspectors, and inspect to support the Diesel Emissions Control Program and the Oxygenated Gasoline Program.

Emissions technical centers evaluate vehicles by appointment only. Please contact the center nearest you to make an appointment: 



Aurora *
15608 E. 18th Ave.
Aurora, CO 80011

* The Aurora Emissions Technical Center also houses the High Altitude Test Facility that provides high altitude motor vehicle emissions testing, collects data for evaluation new strategies to reduce vehicle emissions, tests the emissions performance under a variety of conditions (wintertime driving, oxygenated and alternative fuels, etc.), and tests various emissions-control technologies.


Broomfield 11609 Teller St. 
Broomfield, CO 80020



Denver 2450 W. Second Ave.
Denver, CO 80223



Fort Collins 835 Southeast Frontage Road
Fort Collins, CO 80524
Greeley 2844 W. 30th St.
Greeley, CO 80631
Highlands Ranch 8498 S. Colorado Blvd.
Littleton, CO 80126


Building use criteria

Emissions Technical Centers (ETCs) are state-operated facilities with duties specified in state law to provide support to various Mobile Sources program activities. This includes support to the Gasoline and Diesel emissions inspection programs, fuel sampling and analysis, field inspections and enforcement, and the training and testing of inspection and repair technicians, among other responsibilities.

Requests routinely come from automotive trainers, training committees, vocational schools, industry trade groups, auto clubs, etc. for use of ETCs for various functions. CDPHE honors requests for building use and/or presentations/tours if they are related to ETC functions and statutory purpose, if it is of educational benefit to the public or repair industry, and if it is not competing with a role best met by the private sector.

ETCs are not available for marketing or endorsement of products, or other such functions where private facilities would be more appropriate. Requests are also not honored for research, development, or evaluation of automotive retrofit (add-on) devices, fuel additives, or other automotive products. The U.S. Environmental Protection Agency (EPA) has an established protocol for the evaluation of such devices and additives. All inquiries in regards to fuel additive/retrofit devices should be made to the EPA.

There are several public- and private-sector trainers in Colorado who conduct nationally-recognized automotive technician training classes for diagnosing and repairing Inspection/Maintenance emissions failures. The ETCs are available for use by these trainers to train automotive technicians. Depending on class size and the individual ETC location, one or two classes may be scheduled per evening. Due to space limitation, no more than two classes will be scheduled per evening per facility.

All scheduling, including training by state employees as part of assigned duties, must be arranged at least one month in advance through the ETC supervisor. A signed application and agreement of ETC use stating the purpose of request, curriculum to be taught, and obligating the trainer to cover loss of tools and/or equipment, building or vehicle damage, re-keying the facility due to lost or non-returned keys, etc. will be required before use of any ETC is allowed. Violation of policies will result in denial of access and billing to the person or his/her company for losses as cited above.




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Motor vehicle emissions resources


Smoking vehicle hotline 

The Smoking Vehicle Hotline helps to identify vehicles with excessive emissions, and gives vehicle owners information that will encourage them to make repairs. 

Report a smoking vehicle

by phone: 303-692-3211         

or email:

Please include the vehicle's license plate number and, if possible, whether it is gasoline- or diesel-powered. We’ll then send a letter to the address that on that vehicle's registration. 

Repairs are required if a vehicle fails a mandatory emissions test because of a visible smoke problem. The cause of such smoke must be corrected before the required emissions sticker can be issued.

Local law enforcement can stop a smoking vehicle, issue a ticket and order the owner to make repairs. Colorado law provides for fines of up to $100 (CRS 42-4-314, 412, 413). Some municipalities may impose additional fines for operating a smoking vehicle. 


Engines Off! Idle Reduction Program

School bus drivers, parents, teachers, students and others are turning off their engines whenever parked or stopped for more than one minute. Many fleet drivers also practice this healthy habit.

Idling engines produce thousands of tons of toxic pollution per year in Colorado. Limiting your vehicle’s idling time can dramatically reduce these pollutants and your exposure to them. Engines Off! is designed to reduce toxic vehicle exhaust. 

Please limit your idling whenever possible. It will be good for you, good for your vehicle and good for the air we all breathe!


Engines Off! 


To learn more about this program, please contact: 

Matt Goble

Regional Air Quality Council

303-629-5450 x280 


Small Business Technical Assistance Program (SBTAP)

The Small Business Technical Assistance Program (SBTAP) offers technical assistance to the automotive service and repair industry. SBTAP coordinates technician training, provides testing and repair information to technicians, and works to solve vehicle repair issues.

SBTAP is guided by industry experts who serve on a Diagnostic and Repair Advisory Committee. The committee includes representatives of the automotive service and repair industry, tool and equipment manufacturers and automotive training providers. 


Registered repair facilities

SBTAP maintains a network of registered repair facilities in the Denver Metro and North Front Range areas.

Each registered repair facility receives the following from SBTAP:

  • A sign and banner advertising their registered status.

  • A monthly repair effectiveness report card.

  • A quarterly repair newsletter.

  • Specific-vehicle repair-related information that targets "hard-to fix" vehicles.

  • Priority access to their own repair-related Air Care Colorado website.

Registered repair facilities are listed in a guide given to drivers whose vehicles fail an Air Care Colorado emissions test. This guide ranks facilities in order of their Repair Effectiveness Index. You can use the guide to select repair facilities that have a proven record of repairing emissions-related failures. 


Consumer Assistance for Repairs and Service (CARS) program

The CARS program helps reduce emissions from vehicles that fail emissions tests:

  • CARS provides both you and repair facilities with current information on the emissions repair process.
  • CARS investigates and develops solutions to consumer issues and problems within the inspection and repair process.



To learn more about the CARS program, please contact: 

Bill Haan 

Air Care Colorado 




Tampering of emissions control systems is prohibited!

Who is affected by this notice?

Vehicle owners, operators, automotive/diesel technicians and repair facilities, fleet managers, car and truck dealers, and auto/truck parts retailers.

Why is CDPHE issuing this notice?

It is illegal under state and federal law to tamper with the emissions system of any vehicle. All vehicles (gasoline-or-diesel-powered, and light-or-heavy-duty) are subject to the regulation.

What is the definition of tampering?

Tampering is defined as the disconnecting, deactivating, removing or rendering inoperable any emission control device or element of design installed or engineered by the manufacturer on your vehicle, and is prohibited pursuant to CRS 42-4-314.

All vehicles certified for sale in the United States by U.S. EPA or the California Air Resources Board (CARB) have emission control systems that monitor and regulate the engine operations and exhaust gases to maintain air pollutants at strict levels. Tampering with these devices is illegal: it causes excess pollution, and may cause damage to other emissions control devices on your vehicle.

If you remove, disconnect, detach, deactivate, alter, modify, reprogram, or reduce the effectiveness of any emission control device installed by the manufacturer, or use less-effective replacement parts, then you are committing the act of tampering. This includes reprogramming or “re-flashing” the vehicle’s computer, or installing performance chips to circumvent or “defeat” factory settings, or to produce excessive exhaust smoke (diesel trucks). This also includes modifications such as installing an aftermarket exhaust system (pre-catalyst), or installing larger capacity turbocharger and/or turbo waste-gate modifications.

Tampering with a vehicle will also void its warranty.

Any person other than a manufacturer or dealer who violates this section, or any person who violates the Clean Air Act (CAA § 203(a)(3)(B)), shall be subject to a civil penalty of not more than $3,750 per violation. Any manufacturer or dealer who violates this section shall be subject to a civil penalty of not more than $37,500 per violation.

What is CDPHE doing?

CDPHE is reaching out to vehicle owners, fleet managers, vehicle dealers and enforcement agencies to clarify the tampering prohibition. 

What should I do?

Here is a general (but not complete) list of things to check to ensure compliance:

  • Do not remove, disconnect, detach, deactivate, alter, modify, reprogram or in any way render any emission control device or element of design inoperable or less effective than originally designed.
  • Do not sell, lease, or offer for sale or lease any vehicle with a tampered emissions system.
  • Do not purchase a tampered vehicle from any person, dealer, or auto auction.
  • Do not install any non-compliant emission control devices on your vehicle or engine.
  • Use only emissions control systems replacement parts that are approved by U.S. EPA or CARB.

Additional information: 


For additional information on vehicle tampering, contact the CDPHE Emissions Technical Center: 888-861-2646

or email:

Gasoline-powered vehicles:
Mitch Seek

Diesel-powered vehicles:
Raymond Elick 






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    Low and Zero Emission Vehicles


    Low Emission Vehicle (LEV) Program

    Starting with model year 2022, all new light- and medium-duty vehicles made available for sale in Colorado must be certified as Low Emission Vehicles.



    Please send your contact information to  


    Background information 

    Consumer information, rule development history, etc.



    Please send any questions or comments about the Colorado Low Emission Vehicle programs to


    Aftermarket catalytic converters

    Catalytic Converters

    A catalytic converter is an emissions control device that is installed into the exhaust system on vehicles powered by an internal combustion engine. Catalytic converters reduce toxic pollutants by chemically converting carbon monoxide, unburned hydrocarbons, and oxides of nitrogen into harmless compounds.

    In 2018, the Air Quality Control Commission adopted California’s aftermarket catalytic converter requirements in title 13, California Code of Regulations, section 2222.

    What does this mean for motorists in Colorado?

    Beginning January 1, 2021, all sales or installations of aftermarket catalytic converters for any model year vehicle in Colorado must comply with the Air Quality Control Commission, Regulation Number 20, 5 CCR 1001-24. Either replacement catalytic converters must be original equipment from the manufacturer (OEM), or a new aftermarket catalytic converter certified as meeting California’s Air Resources Board (CARB) emissions standards.

    The California Air Resources Board issues Executive Orders that exempt specific catalytic converters from anti-tampering regulation and laws. This exemption allows "exempted" (approved) catalytic converters to be used in California and in states that have adopted regulations in Title 13, California Code of Regulations, Section 2222. 

    Regulation 20 prohibits the following:

    • Any person to install, sell, offer for sale, or advertise any Aftermarket Catalytic Converter intended for use on any motor vehicle originally equipped with catalytic converter(s) in Colorado unless it has been exempted pursuant to the requirements of California Code of Regulations, Title 13, Section2222 (h) (i.e. a “California Aftermarket Catalytic Converter”).
    • Any person to install, sell, offer for sale, or advertise any used, recycled, or salvaged catalytic converter in Colorado pursuant to the requirements of California Code of Regulations, Title 13, Section 2222 (h) and (i).

    The table below summarizes the types of catalysts that can currently (2020) be used, and what options will be available once the regulatory changes take effect on January 1, 2021:​

    Catalytic Converter Type Currently Legal for Use in Colorado in 2020? Legal for Use Once New Rules Take Effect in 2021?
    New original equipment (OEM) converters
    Yes Yes
    New aftermarket converters
    Yes, if the converter model has been exempted by ARB or are compliant with Federal requirements.
    Yes. Converter models sold or installed on or after January 1, 2021 must be exempted under Colorado Regulation 20.
    Certified used OEM converters
    Yes, if the converter has been tested and approved for resale by an EPA authorized business
    No, used converters may not be sold for use or installed on a vehicle after January 1, 2021.
    Used aftermarket converters or uncertified used OE converters
    No No 


    When Should an Aftermarket Catalytic Converter be Installed?

    A new aftermarket catalytic converter may be installed when the vehicle is beyond its emissions warranty period and a legitimate need for replacement has been established. New vehicles are covered under the federal emissions warranty of 8 years or 80,000 miles and 15 years or 150,000 miles for partial zero emission vehicles (PZEV), whichever comes first. A legitimate need for replacement may be established through the vehicle emissions inspection program. Non-I/M program-related reasons for replacement may include damage resulting from vehicle accidents, cracked or melted substrate, or converter malfunctions.

    If the vehicle is still under the emissions warranty, an OEM catalytic converter must be installed. Aftermarket catalytic converters may only be installed on vehicles beyond the emissions warranty period. You can verify the vehicle's warranty by checking the vehicle owner's manual or warranty booklet, or by contacting an OEM dealership and providing your vehicle identification number (VIN). The vehicle's model year and odometer reading can then be compared to the warranty period and covered mileage.

    There may be instances where a CARB certified aftermarket catalytic converter is not available for a particular vehicle model. In these limited instances, the only option may be an OEM replacement part.

    There may also be cases where neither a CARB certified aftermarket catalytic converter or OEM replacement catalytic converter is available for a particular vehicle model. This would occur where there are no longer any OEM replacement catalytic converters available (e.g., the make was discontinued), and none of the aftermarket catalytic converter manufacturers has received a CARB Executive Order. Contact CDPHE at (888) 861-2646 as there may be a suitable replacement option for a similar vehicle application.

    How to determine what aftermarket catalytic converters are legal for use in Colorado

    If the vehicle requires a CARB-certified catalytic converter, there are several ways to determine the correct catalytic converter to install on a vehicle. The first point of reference should be the catalog provided by the aftermarket catalytic converter manufacturer. Aftermarket catalytic converter manufacturers have hardcopy and electronic versions of their product application guides for both California and Colorado approved converters. These application guides include the part number, make, model, model year, engine family, and engine displacement/test group.

    A listing of approved aftermarket catalytic converters is also available at California’s Air Resources Board website:

    It is important to note that the California aftermarket parts website only provides results for vehicles that have a California-only certification, or vehicles that were dual certified for both California and Federal use. Therefore, some vehicles with a Federal-only certification will not be found in California aftermarket parts database.    

    The CARB aftermarket catalytic converter database provides options to search by vehicle make, model year, model, and engine size; or the installer may enter an executive order (EO) number to determine all applicable vehicles allowed for that EO. Air Resources Board exemptions are issued through Executive Orders. Executive Orders for pre-OBD II and OBD II converters can be sorted by Executive Order number, or by converter manufacturer. Aftermarket catalytic converters sold after January 1, 2009, will also have the CARB Executive Order number permanently labeled on the converter shell.

    Aftermarket Catalytic Converter with indicator descriptions


    Before installation, installers should consult the manufacturer’s catalytic converter application catalog to verify that the converter model is designed to fit the specific vehicle application and that it is specifically approved for use in Colorado. Statements such as “approved for use on OBD II vehicles” does not necessarily mean that the approval is valid for Colorado. If you still have questions, you may contact the CDPHE at (888) 861-2646.

    If a CARB approved aftermarket catalytic converter cannot be identified on the CARB aftermarket catalytic converter website, or in the manufacturer’s catalog; please call (888) 861-2646 for additional guidance. 


    Pursuant to Colorado Revised Statutes section 25-7-122(1)(b), the Colorado Department of Public Health and Environment has the authority to assess monetary penalties to any person who violates any requirements of an emissions control regulation of the Air Quality Control Commission. Any person who violates Regulation Number 20, 5 CCR 1001-24, can be subject to a civil penalty of not more than fifteen thousand dollars ($15,000) per day for each day of such violation.


    Please send questions/comments to  


    Zero Emission Vehicle (ZEV) Program

    As of automotive model year 2023, automakers must make a minimum percentage of Zero Emission Vehicles available for sale as part of their light-duty vehicle offerings in Colorado.



    Automakers can earn early action credits for each ZEV and TZEV they make available for sale in Colorado during model years 2021 and 2022. Please submit any requests to bank early action credits by December 31, 2020. 

    Click here for important additional information for automakers. 


    Consumer information

    Additional information on Zero Emission Vehicles is available through these external resources: 

    Other resources will be added to this list as they become available.  


    Background information

    Colorado ZEV rulemaking history and additional resources.



    Please send any questions or comments about the Colorado Zero Emission Vehicle programs to




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    Frequently asked questions 

    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


    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 at 303-692-3211 or email

    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. 


    • 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.



    • 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.


    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.



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