Defeat device

A defeat device is any motor vehicle hardware, software, or design that interferes with or disables emissions controls under real-world driving conditions, even if the vehicle passes formal emissions testing. The term appears in the US Clean Air Act and European Union regulations, to describe anything that prevents an emissions control system from working, and applies as well to power plants or other air pollution sources, as to automobiles. Use by manufacturers of these devices is considered to have caused many deaths and health problems, a scandal referred to as "Dieselgate". The United States Environmental Protection Agency (EPA) has taken numerous enforcement actions against car makers and other companies that have used or installed defeat devices, whether deliberately, or through error or negligence. While defeat devices were used worldwide, much less remedial action has been taken in other countries. Defeat devices were built into many vehicles by manufacturers, but aftermarket parts or software, such as modified exhausts and chip tuning products and services, are considered defeat devices if they inhibit or bypass a vehicle's emissions controls.