On Mon, 21 Sep 2015 21:44:12 -0700, Sam Wilhelm wrote:

How did this alleged cheat work exactly?

http://www.greencarreports.com/news/...estions/page-2
(4) What exactly did VW do?

Volkswagen has admitted that it equipped the control software for its
2.0-liter TDI diesel vehicles with a "defeat device" that detected when the
car was undergoing emissions testing and significantly changed the
operations of its powertrain to reduce emissions during the tests.

That detection was likely based on a combination of sensor data from the
car, which might include steering angle (since cars on dynamometer tests
don't make turns), front-wheel versus rear-wheel rotation speed, and a
variety of other factors.

It appears that a combination of the factors above plus extremely gentle
acceleration and braking might alert the car that it wasn't on the road but
being tested in a lab.