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National Compliance Initiative: Stopping Aftermarket Defeat Devices for Vehicles and Engines


Mobile sources are a significant contributor to air pollution. The EPA, through its direct implementation authority, can play a critical role in addressing these important pollutant sources. Title II of the Clean Air Act (CAA) authorizes the EPA to set standards applicable to emissions from a variety of vehicles and engines. Required emission controls often include filters and catalysts installed in the vehicle’s or engine’s exhaust system, as well as calibrations that manage fueling strategy and other operations in the engine itself. The CAA prohibits tampering with emissions controls, as well as manufacturing, selling, and installing aftermarket devices intended to defeat those controls. The EPA has found numerous companies and individuals that have manufactured and sold both hardware and software specifically designed to defeat required emissions controls on vehicles and engines used on public roads as well as on nonroad vehicles and engines. Illegally-modified vehicles and engines contribute substantial excess pollution that harms public health and impedes efforts by the EPA, tribes, states, and local agencies to plan for and attain air quality standards.

FY 2020-2023 Update

This new NCI will be implemented during FY 2020-2023.


This NCI will focus on stopping the manufacture, sale, and installation of defeat devices on vehicles and engines used on public roads as well as on nonroad vehicles and engines.