Federal investigators couldn't figure out why perfectly good fuel pumps were failing in some Volkswagen (and Audi) vehicles. The investigation lasted 4 years and had VW's full cooperation.
The pumps seemed fine and even came with built-in margins for fuels that were slightly out of specification. What the pumps couldn't handle is owners filling up their diesel engines with gasoline.
For the love of everything, don't do that!
Using gas for diesel engines would be like trying to replace my morning coffee with soy milk. Sure, I could swallow it but the result wouldn't be pretty. A little gas in a diesel engine will burn quickly and create a very low power output. A lot of gas in a diesel engine can cause the engine to blow or, you guessed it --- fuel pump to fail.
In 2013, VW started a service campaign to install bright yellow stickers near the gas cap to warn owners not to let this happen.
Full story on carcomplaints.com