Dear Mr. Anderson:

Thank you for your response. Modifications to motor vehicle emission control systems or elements of design are governed by the tampering prohibition section of the federal Clean Air Act, Section 203(a)(3)(A), 42 U.S.C. § 7522(a)(3)(A). Section 203(a)(3)(A) prohibits any person from knowingly removing or rendering inoperative an automotive emission control device or element of design after sale and delivery of the motor vehicle to the ultimate purchaser. Furthermore, section 203(a)(3)(B) of the act goes on to prohibit the manufacture, sale, or installation of devices which defeat or bypass an emission control device or element of design. These are referred to as defeat devices. Individuals or repair shops that violate these sections of the Clean Air Act are subject to civil penalties of no more than $2,500 (which is now $2,750 for current violations) per vehicle or per defeat device. Manufacturers and dealers who violate section 203(a)(3)(A) are subject to civil penalties of no more than $31,500 per vehicle.

Basically, if you alter a vehicle from its certified configuration with respect to the emissions control system, it could be considered tampering. Contacting the vehicle manufacturer is the best way to get the complete list of emissions components and systems on your vehicle. Since every vehicle design is different, EPA cannot keep a complete list for every vehicle configuration that is on the market. The emissions warranty booklet may also be a source for that information.

Many aftermarket parts marketed to improve vehicle performance fall into the defeat device category. Manufacture and sale of such parts are clearly prohibited and these violations are enforced by EPA. However, not all aftermarket parts are considered defeat devices. Many aftermarket parts are intended to be used to repair or modify a vehicle without adversely affecting emissions performance. EPA has issued an enforcement policy called Memo 1A to clarify under what conditions these components could be sold or used without being considered tampering which is available on the EPA web site at:  www2.epa.gov/enforcement/memorandum-1a-tampering-enforcement-policy-alternative-fuel-aftermarket-conversions.

Essentially, it states that an aftermarket part can be used or a vehicle can be modified if there is reasonable basis for knowing that it will not adversely affect emissions performance. When an aftermarket replacement part or a rebuilt part is used for the purpose of maintenance or repair of a vehicle, a reasonable basis is considered to exist if the individual performing the repair reasonably believes that the replacement /rebuilt part is designed to perform the same function with respect to emission control as the original part, or the replacement/rebuilt part is represented in writing by the part manufacturer to perform the same function with respect to emission control as the original part.

When an aftermarket part is manufactured, sold, or installed as an add-on, auxiliary, augmenting, or secondary part or system (e.g. a performance enhancing part), or when an individual modifies a vehicle, emissions tests conducted according to the federal test procedure are required to establish a reasonable basis for knowing that emissions performance will not be adversely affected. Additionally, the on-board diagnostics (OBD) system on vehicles is considered to be an emissions control system or element of design. The manufacturer or installer of an aftermarket part or an individual modifying a vehicle will need to have a reasonable basis for knowing that the OBD system functionality will not be affected.  

A reasonable basis is considered to exist if: (a) the installer knows of emissions tests which have been performed according to the federal test procedure showing that the act does not cause similar vehicles or engines to fail to meet applicable emission standards for their useful lives; or (b) the part or system manufacturer represents in writing that tests as described in (a) have been performed.

The California Air Resources Board (CARB) has a program to certify aftermarket parts based on testing performed by the part manufacturer. This program is actively used by many aftermarket parts manufacturers that sell parts nationwide. EPA would likely regard CARB Executive Order approval as reasonable basis for use of the CARB approved parts outside of California. For more information on this program, please visit the CARB web site at: www.arb.ca.gov/msprog/aftermkt/aftermkt.htm.

If you know of potential tampering violations, please fill out the form that is on EPA's web site at www.epa.gov/tips.

We hope this information is helpful. Thank you for contacting the Office of Transportation and Air Quality.

Sincerely,

Jennifer France

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Public Information Services
Office of Transportation and Air Quality
U.S. Environmental Protection Agency