I thought I would post this as another thing for people to check. Back in April, I had my system recharged because wasn't working properly. It had half the coolant required. They added a dye to it when they recharged it. I just went in today, because about two weeks ago, I started getting the econo mode intermittently. Well the dye did its job and revealed a slow leak with the schrader valve. They replaced the schrader valve and recharged it for $55.
Luckily, the didn't have to replace the complete hose. I know this wont be the answer for everybody, but I am sure in the Audi world, it will happen to someone else sometime.

 

good info to know! thanks for sharing