It's only for the engines that are not running urea injection, which is the only way all the other manufactures can pass NOx emissions and oddly all the new VW/Audi 2015 models now have.
I don't think they've figured out exactly what they did but I've read the ECU was programmed on all the vehicles to detect when it was being tested using the wheel and steering sensors. If the front wheels were spinning with the rear wheels stationary and there was no steering input then the computer could assume it was being tested and modify the fuel/timing. I haven't seen anything explaining how it would differentiate between an emissions test and a dyno.