MaxD

2003 A4 1.8t Avant Quattro, 84,000 miles.

First real warm weather here in Denver, and on comes my CEL. I recently completed 80K service (oil, timing belt/water pump, air filter(s), plugs).

Ran VAGCOM and here are the codes:

I'm just starting to troubleshoot this, but if anyone has thoughts on damage I might do by continuing to drive the car until I figure it out, I'd be much obliged.

Thanks in advance.

ryan_qttro

Check your crankcase vent hose, the big 3 way tube off the back of valve cover. It meets up with a plastic hose and is held with a very strong metal clip, after awhile the plastic hose becomes brittle and breaks where the metal Clip holds it as it enters the rubber 3 way tube

MaxD

The crankcase vent hose and its couplings looks in pretty good shape from the front. I'll look with a mirror in the daylight.

There's definitely a check valve or something that is eaten all up by corrosion behind/above the airbox:



Could that be the culprit?

MaxD

The leak is a fractured check valve at the rear of the valve cover, in pretty tight quarters:



Now I just need to figure out: Will any check valve do? Or do I need a specific part #? It doesn't look exactly like the really basic check valves sold all over the place for $13.

MaxD

Replaced both parts, cleared CEL and everything seems back to normal... maybe better than normal as performance seems better. The leaks may have been sapping power.

The parts were very expensive from Audi dealer. I ordered them online and even with overnight shipping I saved $30 off the dealer price. Part numbers were:

Crankcase Vent Valve
Mfg Part# 06A133528D

Vacuum Check Valve
Mfg Part# 058905291K

The Crankcase Vent Valve was kind of a pain, just because of the extremely tight quarters and single-use hose clamps Audi uses. But got it done and back running.

lyleswk

Good info. Thanks for posting. I am always amazed how very simple problems look bad when you first look at them and turn out to be very simle to fix. I had lean running condition on a Z31 Nissan turbo that was a simply the O2 sensor. This after many many hours of troubleshooting and over thinking. Removing the O2 sensor on a 27 year old car is not simple, but she is fixed