Audi utvecklade teknik för VW-fusket redan 1999

A defeat device, as defined by the United States Environmental Protection Agency (EPA), is any apparatus that unduly reduces the effectiveness of emissions control systems under conditions a vehicle may reasonably be expected to experience. Defeat devices are also forbidden in the European Union, and the use of a defeat device is subject to a penalty. The term originates from the US Clean Air Act, and refers to anything that prevents an emissions control system from working. The EPA has taken numerous enforcement actions against companies that have deliberately, or through error or negligence, allowed defeat devices to interfere with pollution controls at power plants, in motor vehicles, and elsewhere. Aftermarket car parts and accessories, such as exhaust or fuel system modification components, which affect emissions, are considered defeat devices.