b6beast

Hello, I am a new member but not new to the site. I've visited countless times to solve car issues but now i have a problem I can't seem to figure out.

My father and I replaced the timing belt and water pump about 2 weeks ago on my 2005 1.8T A4, but before that there was an MIL saying "Turbocharger under boost." My father says it is more than likely the diverter valve, but I'm not sure. Yesterday the fuel cap open light came up on the center display, so I clicked it about 5 times (I usually click it 3 times) to see if it would disappear. The warning was still there, so I reset it. Then, on my way to the parts store the oil sensor light came on for about a minute, then disappeared. I asked the guy at the counter and he didn't exactly know either. I'm thinking and hoping it's an electrical issue and not mechanical, the turbo still spools and the wastegate opens, so i don't think it's and issue with the turbo assembly. I cleared the under boost code yesterday and it has yet to come back on, usually when im getting on the highway and in the higher RPM range.

The car seems to run fine and upon checking the oil levels, it was not low at all. Hopefully it is the diverter, but I don't think that would have any connection with the oil sensor warning.

Thank You!

lyleswk

I doubt all those are related.

1) Oil level light, which is the yellow one, not the red pressure light: Assume you checked your oil level Assuming you did, just buy an OEM sensor and replace next time you change the oil. Don't get a cheap knockoff
2) I get the underboost fault about every 3 months or so when i get on it a little too hard at highway speeds just like you. I assume you are using a VAGCOM reader and are getting P0299 (see link below for troubleshooting)? Anyway, I will check that it is that fault I get. I don't clear it; I let it clear itself. Usually takes 4 or 5 drives. Not sure why other than it makes me feels like the issue that is causing it is intermittent.
3) You may be looking at a new cap.

16683/P0299/000665 - Ross-Tech Wiki

b6beast

lyleswk

I checked and that's is the intermittent fault I get. I had my front clip off to replace the fan module last summer and decided to replace the diverter valve and still get the fault, so my issue is not that.

david9999

Check hoses throughout and make sure they are tight if you have not.