That doesn't sound right. West Virginia University's 2014 report to the ICCT only included 3 cars, 2 of which were VWs. There's a unpublished report by WVU with suspicions on Fiat-Chrysler, but that's been floating around this year. The EPA did reprimand 6 manufacturers including GM & Ford for defeat devices, but that was back in 1973. There's a civil class action brewing against GM truck diesels and I understand that Germany has been recently looking into emissions of the Ford Mondeo, but neither of them are via the actions of the EPA.

>Prosecution started in 2015, and only against VW.

Why not? They were the ones that fraudulently claimed they could achieve low emissions without urea injection, used defeat devices, and impeded the investigation into their malfeasance.

Yes, I don't understand why only VW is being prosecuted when it was/is most car makers cheating tests.

This is like when the US went after the Swiss Banks which paid Billions in fines, yet none of the US banks got in trouble although they where all doing the same thing.