The Environmental Protection Agency (EPA) in United States is accusing Volkswagen and Audi of using a "defeat device" on approximately 482,000 cars for cheating during official emissions tests.

The software in question was used on the Volkswagen Beetle, Golf, Jetta and Audi A3 for the 2009-2015 model years and also on the Volkswagen Passat 2014MY and 2015MY. All these vehicles come equipped with a four-cylinder 2.0-liter turbodiesel engine and have a special software that was able to automatically detect when the car was undergoing EPA emissions testing and it turned on the car's full emissions controls device. After that, the software switched off the device during rear world driving.

This is the explanation given by EPA and they say the software allowed all those VW and Audi models to fully comply with the emissions standards during lab testing, but in real-word driving the nitrogen oxides emissions are up to 40 times above the allowable levels.

Under the current federal law, EPA can apply a maximum fine of $37,500 per car which means Volkswagen and Audi could face a total fine of up to $18 billion.