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Tampering of Vehicle Emission Controls

Defines "tampering" and what kinds of vehicle repairs can be made to correct tampering. Texas law prohibits selling or leasing tampered vehicles.


Definition of "Tampering"

Tampering is removing or making inoperable any system or device used to control emissions from a motor vehicle engine. The motor vehicle is defined as any self-propelled vehicle designed for transporting persons or property on a street or highway. The only exception to the tampering rule is the need to install a new certified emission control system or device that is equally effective in reducing vehicle emissions.

Tampering may include, but is not limited to:

  • Removing the catalytic converter, air pump, and exhaust gas recirculation (EGR) valve, or doing anything to keep them from working properly, such as disconnecting vacuum lines and electrical or mechanical parts of the pollution control system.

  • Adjusting any element of a car or truck's emission control design so that it no longer meets the manufacturer's specifications.

  • Installing a replacement part that is not the same in design and function as the part that was originally on the vehicle.

  • Adding a part that was not originally certified on the car, such as installing a turbocharger.

The U.S. Environmental Protection Agency's (EPA) anti-tampering enforcement policy is covered under the provisions of Mobile Source Enforcement Memorandum No. 1A.Exit the TCEQ This policy states that the EPA will not consider any modification to a certified configuration to be a violation of federal law if there is a reasonable basis that emissions are not adversely affected. A certified configuration is an engine or engine-chassis design that has been certified or approved by the EPA to meet certain emission standards prior to the production of vehicles with that specific design. Evidence of federally approved testing must be available upon request.

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Vehicle Repairs

Anyone can perform the necessary work on a vehicle to correct tampering-related problems, although it is recommended that the services of a facility with experienced repair technicians be used. Vehicle warranties usually cover emission control systems and devices. However, if these components are tampered with, the manufacturer may not honor the warranty because the car has not been maintained according to the manufacturer's specifications.

You may remove an emission system or device at any time if you are replacing it with one that is specified for that vehicle and is equally effective in reducing emissions. For example, it is acceptable to replace the engine of a vehicle if:

  • the replacement engine is certified by the EPA;

  • the replacement engine is compatible with the vehicle chassis and all applicable emission control systems and devices are properly installed and operable; and

  • the resulting vehicle is identical, with regard to all emission-related parts and engine design parameters and calibrations, to the same or a newer model year vehicle, as originally equipped.

A damaged or missing catalytic converter may be replaced with an original equipment manufacturer's catalytic converter certified for that vehicle or an aftermarket catalytic converter that meets the emissions requirement for that vehicle. However, all aftermarket converters must be certified and assigned an EPA number. The EPA number should be visible.

An older engine may be installed in a newer chassis if all emission control systems and devices are connected, including the exhaust system and catalytic converter, and the resulting engine-chassis configuration conforms to the engine configuration of the model year of the chassis or newer. It is illegal for anyone to change a vehicle into an older configuration.

A diesel engine may not be replaced by a gasoline engine if the manufacturer did not offer such an engine configuration for that model year chassis.

A catalytic converter may not be removed from a motor vehicle that is currently being used only for off-road driving. This is considered tampering. Tampering provisions pertain to all self-propelled motor vehicles originally designed for transporting persons or property on a street or highway.

A single exhaust system may not be replaced with dual exhaust unless the vehicle's manufacturer certified an identical engine-chassis configuration for that model year of vehicle or newer that includes such an exhaust configuration. The exhaust system configuration is specified by the vehicle manufacturer because engines and some of the associated emissions systems are generally affected by the exhaust system backpressure, which in turn affects vehicle emissions. Therefore, the installation of a dual exhaust system with two converters in the place of a single exhaust system would be considered tampering.

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Vehicle Sales

Texas law prohibits any person from selling, offering for sale, leasing, or offering to lease any vehicle not equipped with all emission control systems or devices in good operable condition. Violators are subject to penalties under the Texas Clean Air Act of up to $25,000 per violation. Buyers are advised to have the vehicle checked for all required emission control devices prior to purchasing a new or used vehicle.

A vehicle may not be legally sold if its original engine has been replaced with another certified engine but without the related emission control components. Tampering includes the failure to install the emission controls associated with an engine configuration.

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Alternative Fuel Conversions

The installation of alternative fuel conversion equipment is not considered tampering if acceptable emission reductions are verified by certification of the vehicle through the federal Small Volume Manufacturer Certification Procedures, the EPA full certification process, or through the federal emissions test procedures described in EPA's Mobile Source anti-tampering policies relating to alternative fuel conversions. Exit the TCEQ

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More Information

For more information on EPA's anti-tampering policies and enforcement, call EPA's Enforcement DivisionExit the TCEQ at 202/564-0652.

For more information about state regulations and policies against tampering, please call Amy Muttoni of TCEQ's Mobile Source Team at (512) 239-6351.

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Related Rules

Title 30 Texas Administrative Code 114.20-114.21 — Motor Vehicle Anti-Tampering Requirements

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