[anarcticpuffin]

I'm wondering how they detect that they're in an emissions test quickly enough to not emit too much early in the test. Do the testers connect their equipment to the OBD-II port of the car? Or I guess you could tell from the fact that one set of wheels is spinning while the other wheels are stationary (because it's mounted on a dynamometer).

[anarcticpuffin]

I found a bit of an answer. According to this EPA document, it detected a test by sensing the position of the steering wheel, vehicle speed, duration of engine operation and barometric pressure.

http://www3.epa.gov/otaq/cert/documents/vw-nov-caa-09-18-15....

[trashcan]

Everything I have read is that the defeat was activated when the car was in use, but not in motion (probably on something like a dyno). It was discovered by testing with portable sensors to measure the pollutants while the car was driving on the road.

[fancyketchup]

The test protocol is a fairly specific schedule of engine power demands, is it not? It seems like one could look for any behavior outside of what is expected from the test, and then activate the 'defeat device.'