On Mon, 21 Sep 2015 12:57:34 +0000 (UTC), Ewald Böhm wrote:

My question is HOW did the car *know* it was being *tested* for emissions?

The best answer to the question seems to be here, as noted by Sofa Slug:

http://www.rocketnews.com/2015/09/did-volkswagen-cheat/
http://www.latimes.com/opinion/edito...919-story.html

Staying on topic, this article says the cheat only worked when there was a
DYNO involved!
http://www.chron.com/business/energy...on-6520088.php

Here are the contiguous quotes:
(begin quote)
VW used secret software €” an algorithm that detects when cars are being
tested on treadmill-like devices called dynamometers, and stealthily
switches the engines to a cleaner mode.

Because *smog tests are almost always done on dynamometers*, VW got away
with the scheme for seven years, until the "clean transportation" advocates
went to West Virginia University, which tests emissions using equipment
that fits in car trunks.
(end quote)