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 is 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.

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. Aftermarket parts or software, such modified exhausts or chip tuning products and services, are considered defeat devices if they inhibit or bypass a vehicle's emissions controls.

In 1973 the Big 3 Detroit automakers, Chrysler, Ford Motor Company and General Motors, along with import brand Toyota, were ordered by the EPA to stop using ambient temperature switches which disabled pollution controls at low temperatures. The automakers agreed to cease using the ambient temperature switches in the way the EPA said was in violation of the Clean Air Act, while insisting that the switches were not 'defeat devices' intended to evade rules. The auto companies said the devices improved engine efficiency and actually reduced pollution. The EPA order affected 2 million 1973 model year cars slated for production, but did not require a recall of cars already on the road.

Also in 1973, Volkswagen agreed to a settlement with the EPA, in which they admitted no wrongdoing and paid a $120,000 fine, for failing to disclose the existence of two temperature sensing switches that affected emissions function. In their 1974 model year application to the EPA, VW disclosed the presence of the switches and the EPA rejected them, so they were removed.

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