Hey guys

My 02 A6 4.2L has been throwing P0492 for a few months. I've tried fixing it since I need the CEL off to smog it. Everything I google seems to lead me to something I've already tried! Here's what I've tried so far:
--Checked vac lines as best as I could--nada
--Switched air pumps with my boyfriend's 03 S6--my CEL stayed on, his stayed off.
--Replaced the air filter--I know this really doesn't have much to do with this, but a K&N is much better anyway
--Replaced one of the N112s (solenoids) at the front of the engine, seemed like it had a bad line, replaced it--CEL stayed on.
**Haven't tested the kombi-valves, since those seem like SUCH a pain, and my free time during daylight is few and far between these days, but I don't even know how to test them if I got them out!

The newest issue: P0492 added his bff P0491! AHH. I feel like it could have something to do with something attaching to the air pump, as my old air pump sounded like a jet taking off (that now my boyfriend's car sounds like ), and the "new" one was fine, but now, I swear I hear it getting high pitched again. Maybe I'm just going insane from trying to figure this out, though.
I am at a complete loss now! If anyone could help shed some light on anything I missed or need to/should check, I would be forever grateful! I start fall semester soon and can't park on campus with expired reg unless I want vast amounts of tickets!

Thanks for any help!!

 

P0492 and P0491 usually go hand in hand. Basically it is telling you that the secondary air injection failed for both banks (hence 2 codes).
I had the same codes on my car (same as yours) - and it turns out it was the big hose from the SAI going directly into the intake manifold (rear of the engine). It had a huge hole on the bottom side of the hose (near the engine) so I couldn't see it until I took it out.
Audi wants 100$ for that hose, or go to a local car parts shop and get a heater hose for 10$
This is just one suggestion. Seeing that you already replaced the pump itself and checked the vacuum lines it will get tougher if it isn't that hose I mentioned.

 

Just picked up 2002 A6 4.2 that threw the P0492 CEL after a couple of weeks. After poking around for a couple of weeks, but not digging in properly, I took it to an independent shop. So embarrassed when they said there was a hole in the hose. The Audi hose was $190. Stunning price since it doesn't have fuel or coolant under pressure flowing through it.

Lesson learned, pull the whole hose out and inspect it. Casual visual inspection from under the car with flashlight is insufficient.

Great advice here, when you choose to follow it.