The Environmental Protection Agency accused the German automaker of using software to detect when the car is undergoing its periodic state emissions testing. Only during such tests are the cars’ full emissions control systems turned on. During normal driving situations, the controls are turned off, allowing the cars to spew as much as 40 times as much pollution as allowed under the Clean Air Act, the E.P.A. said.
This will be interesting.
It's one thing to use cycle-beating to exaggerate real-world performance, but this time it looks like VW have been pinged for doing something far more sneaky and deliberate.
The cynic in me may lead me to conclude that EU authorities may have been prepared to turn a bit of a blind eye because of the economic importance of the car industry. Uncle Sam might not be so forgiving when AFAIK, VAG don't have production in the US (though VW are Borg Warner's largest customer for DSG dual-clutch auto transmissions, I believe most of that DSG production is outside the US).