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?

As of January 1, 2021, all sales or installations of aftermarket catalytic converters for any model year vehicle in Colorado must comply with Air Quality Control Commission Regulation Number 20. 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 regulations 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, Section 2222 (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 following table summarizes the types of catalysts and options that are available once these regulatory changes took effect on January 1, 2021:​

Catalytic Converter TypeLegal for Use Once New Rules Take Effect in 2021?
New original equipment (OEM) converters
New aftermarket converters
Yes. Converter models sold or installed on or after January 1, 2021 must be exempted under Colorado Regulation 20.
Certified used OEM converters
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


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 printed and electronic versions of their product application guides for converters that have been approved by both California and Colorado. 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: https://ssl.arb.ca.gov/AftermarketParts/catalysts

It is important to note that the California aftermarket parts website only provides results for vehicles that have California-only certification, or for vehicles that were dual certified for both California and Federal use. Therefore, some vehicles with a Federal-only certification will not be found in the 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 CDPHE at (888) 861-2646 or CDPHE_mobile@state.co.us.

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. 

Colorado Non-compliant Catalytic Converters

If you believe that a catalytic converter has been installed that does not comply with Air Quality Control Commission Regulation Number 20, file a complain using the form below:

Colorado Non-compliant Catalytic Converter Complaint Form


Pursuant to Colorado Revised Statutes Section 25-7-122(1)(b), CDPHE 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, is subject to a civil penalty of not more than forty-seven thousand three hundred fifty-seven ($47,357) dollars per day for each day of the violation. 

Webinar: "Understanding Colorado's New Aftermarket Catalytic Converter Regulation"

CDPHE hosted webinars in January 2021 to explain new requirements for aftermarket catalytic converters.

Presentation Slide Deck (PDF) 




Please send questions/comments to CDPHE_mobile@state.co.us