IMHO besides VW others outside Germany should be punished too.
https://en.wikipedia.org/w/index.php?title=Volkswagen_emissions_violations&oldid=683264419

The U.S. test results confirmed the ICCT's findings in Europe.[37] The
West Virginia scientists didn't identify the defeat device, but reported
their findings in a study they presented directly to the EPA and CARB in
May 2014.[41][42]
And in 2013 there was warning about "defeat device"

There probably isn't any specific "defeat device".  These days, probably all fuel engines are controlled by complex computer programs, that take various inputs (ambient temperature, ambient air pressure, engine temperature, and perhaps others) and make complicated adjustments in inputs to the engine, in order to make the engine run better in various ways.  In other words, the "defeat device" is in the software, not the hardware.

               Jim bell