How VW Cheated on the EPA Test

There is a nice and succinct article by by Andrea Peterson and Brian Fung titled:

The tech behind how Volkswagen tricked emissions tests

 Here is how they did it from the article:

"In the end, the detailed requirements for each test gave Volkswagen the advance knowledge it needed to teach its cars when to behave more cleanly. By measuring how long the engine was running, the vehicle’s speeds, and even seemingly esoteric factors, such as the position of the steering wheel and barometric pressure, Volkswagen vehicles could understand they were being tested and so adjusted their engine performance to pass the tests, according to the EPA."

The article is well worth reaching.