EPA details how VW software thwarted emission tests

The software used by Volkswagen to get around environmental standards in some 11 million vehicles effectively told each car to go into a "clean mode" when it detected the car was being tested for emissions.
Details about how the automaker was able to elude emissions testing -- the "defeat device," as the software has been called -- is included in a Sept. 18 letter from the Environment Protection Agency (EPA) to Volkswagen.
That letter prompted VW to admit that half a million Volkswagens and Aud