According to statements by the Environmental Protection Agency, Volkswagen is using software to detect when the car is undergoing its periodic state emissions testing. Only during such tests are the cars' full emissions control systems turned on. During normal driving situations, the controls are turned off, allowing the vehicles to emit as much as 40 times the amount of pollution mandated under the Clean Air Act.
EPA officials have issued Volkswagen with a notice of violation and said the automaker had admitted to the use of a so-called defeat device.
The software installed in the vehicles which are being recalled, is designed to hide nitrogen oxide emissions. Nitrogen oxide is a pollutant that contributes to the creation of ozone and smog, and is linked to a range of health problems, including asthma and respiratory diseases, and premature death.