The EU did not prevent Dieselgate because the EU was lacking the regulatory framework to do so. And after Dieselgate, lots of new laws were put into place to address a market wide breach of consumer law (the representative actions directive and the omnibus directive). That is exactly what a good governing body should do: act within the boundaries of the law, and improve the law when something bad happens. I very much doubt it will happen again. We are talking billions in fines before there was an actual framework in place to address this. Today the result could be in the tens of billions.