The knowledge you can get from a 5 year old post is amazing. Thanks to PaulW and everyone else who contributed in this thread. Really good stuff here.

I've an '01 A6 4.2 that's throwing P1423 and P1411 codes. These are the "secondary air injector" codes you guys are talking of. I've read another post where someone was using the Output Test with a VAG-Com and noticed leaking air during these tests. I'm running into the same thing. As soon as I start the output test, I hear a hiss, that I can't locate. As I let the output test run I hear all sorts of relays/fans/valves working. But I always hear that hiss.

Could this be the way it's supposed to be? Or do I just have a leak I can't find? Please stop me before I rip my engine compartment to shreds trying to find a hiss that's supposed to be there! Haha!

Brian

2001 A6 4.2 loaded minus nav (83k mi)
ECS Tuning Slotted Rotos Front & Back
Mintex Red Box

32 tranny recode
recoded central locks

looking at VAST ECU/TCU
trying to come up with custom exhaust
my cats are on their way out (see above comment)
need timing belt soon
one of my headlight motors is f'd up