Eagleone1

My daughter's car is a 05 Passat with a 1.8T, same as my wife's A4.
The issue is her oil warning light will illuminate but it only happens when she is on the interstate. I have had it at the dealer and they mentioned sludge (I have receipts showing nothing but full synthetic in the car as far back as 07, we are third owner), of course without pulling the valve cover or oil pan to confirm. I talked with a mechanic buddy and his recommendation is to have the engine chemically flushed, which I did. Picking up the car from the garage and they informed me there was really nothing of note from the flush and they did not see any sludge. Yesterday, the same issue with the warning light and we had to have it towed to a garage because she was 100 miles from home and in a snow storm. The oil pressure is normal according to the garage and they can't get the light to come back on. I don't want to use the shotgun approach trying to fix it. Anyone have an idea or this issue before?

x19

I think that your engine has 2 oil pressure sensor and one is just above oil filter body and the other one is on cylinder head( back of head) I think, these switch become weaken some time. Good luck and Happy Holidays. x19

Prospeeder

The sensor is cheap, try replacing it. If it still comes back, remove the pan, no chemical flush will touch the stuff. Its not really like sludge you see in other cars. Its oil coke from the turbo, its hard as a rock and packs into the fine mesh screen in the pickup tube. Its common if run low on oil, not using synthetic, using synthetic but not changing it evey 5k-6k miles or not keeping it topped off, and running the car hard, and then turning it off right away. This burns the oil in the turbo and then it flushes down into the oil pan and is picked up. You have to replace the pickup tube or chisel the stuff out and be certain its clear.

Eagleone1

Update... I replaced the sensor and it did not work. I sent it to a German garage and they found a lot of issues. Pulled the oil pan and the pickup tube was clogged with sludge. Replaced the oil pump, oil screen, cleaned the pick up tube and had to replace the rod bearings. Turned out Dealership was correct, by default. The garage only charged $953 to do it all! Dealership wanted around $1200 just to replace pick up tube. Car is running great. Knowing the car has only seen synthetic oil the sludge issue is a bit of a boggle.

Prospeeder

Synthetic oil will do it also if its left in too long. 5k miles needs to be your oil change intervals with 5w40 synthetic. Running the oil too long causes it to loose to ability to withstand extreme temperatures, the hot turbo will cook the oil to the little particles that run down the turbo drain into the pan and pack into the pickup tube, which is why you can remove the valve cover and its spotless. I really wouldnt call it sludge, its more like oil coke.

Eagleone1

Thanks for the explanation, that make sense.

Nawdyaudi

Thank you Prospeeder and Eagleone! I am female and HATE going to the dealership for repairs or any garage for that matter. Audi Dealership was going to charge me for sensors, spark plugs, and some other stuff in addition fix this oil sludge issue...around $2500. But after reading this forum, I was able to research the red oil lamp pressure off/on and the sludge and coking issue in the 2004 a4 1.8l turbo engines and at least go in with my game face...instead of a sucker face. Also, the car is idling higher than usual- 900 usually, since this started it idles around 1100. Service said it was misfiring as well - the need for new spark plugs? Car has 101,000. All services up to date. thanks guys and or gals!

Eagleone1

Are you in the Denver Area? You really need to get a Vag Com and run the diagnostic. It could be a lot of things. Plugs, coil pack, leak in the PCV system... etc. Seeing it has over 100,000 miles I would start to look at the PCV hoses. They tend to crack a LOT! The lower portion that runs from your valve cover down to the crank case breather hose is a web of hoses and would cost around $400.00 just for the parts. If that is the case, check out 034 Motorsports for replacement. That web of hoses they redesigned into just 3 and better quality. We have about 2500 miles on the hoses and no issues.