Aftermarket, Performance and Add-On Parts

This page last reviewed January 16, 2019

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What's under the hood is important to air quality.  Automotive emissions account for over 50 percent of all smog-forming pollutants in California. To improve air  quality, the California Air Resources Board (ARB) requires vehicle manufacturers to develop engine and emission equipment systems that reduce the specific pollutants that cause California's severe air quality problem. These emission control systems are also  required to be proven durable and reliable.

To ensure that these systems operate as designed, California Vehicle Code Section 27156 and the Federal Clean Air Act prohibit modifications that increase motor vehicle emissions. Since if properly designed, most performance modifications do not increase vehicle emissions, these same laws also allow the installation of parts or modifications proven by their manufacturers and the ARB not to increase vehicle emissions.

All aftermarket parts sold in California belong to one of the following four groups:

1.   Replacement Parts- Replacement Parts Guide
2.   Legal Add-On or Modified Parts (Executive Order Parts) -   Aftermarket Parts Database
3.   Competition or Racing Use Only Parts -   Exemptions for Uncontrolled Vehicles
4.   Catalytic Converters

Additional Information for Manufacturers of Aftermarket Parts:

An exemption from Vehicle Code Section 27156 (VC 27156), California's anti-tampering law, is required before any add-on or modified part can be sold in California. Manufacturers interested in obtaining a VC 27156 exemption for an add-on or a modified part should fill-out and submit an application form to the ARB for evaluation. Detailed information on how to do this can be obtained from the document, "Procedures for Exemption of Add-On and Modified Parts," amended June 1, 1990. (PDF - 2.54MB)

What's New:

Work Group (1/22/19): Aftermarket Parts Procedures Work Group - Intercooler Kits or Modifications to the Stock Intercooler System.

  • Webinar Information: Aftermarket Parts Procedures Work Group - Intercooler Kits or Modifications to the Stock Intercooler System.
  • Work Group Agenda: Aftermarket Parts Procedures Work Group - Intercooler Kits or Modifications to the Stock Intercooler System 1/22/2019. (PDF - 82K)

Aftermarket Parts related Workshops and Meetings:

For a complete listing of Public Workshops and Meetings, please visit the Aftermarket Parts Public Meetings wepbpage.

Aftermarket Parts Mailings List Information:

Amendments to the Aftermarket Parts Regulations: If you would like to participate in future meetings, or get future workgroup announcements, please subscribe to the: Aftermarket, Performance and Add-On Parts (aftermkt) Topic List.

Heavy-Duty Diesel Retrofit Device Emission Reduction Verification:  

Recently, the Air Resources Board initiated a number of incentive programs to offer funds for retrofitting existing heavy-duty engines in public and private fleets to reduce PM and NOx emissions. Retrofit systems to be used in any PM or NOx incentive program must be evaluated and certified for their emission reducing capabilities. Applicants who plan to participate in any of the ARB's retrofit programs may obtain additional information by viewing the ARB's Diesel Mobile Programs website.

Evaluation of Omstar D-1280X Fuel Additive:

Who can I contact for more information?

For more information, please contact ARB's Public Information Helpline at  (800) 242-4450.