1.8T aux air pump/systems Q

Old man has an A6 1.8T (circa 2000), for a year or so it's had an intermittent 'aux air leak' fault code, sometimes it goes away for 200 miles then it pops back on.
Seems that there's a pump of some kind low down on the block that releases air into the airbox every now and then and that seems to be the cause, it's got loads of water from condensation? in it and audi want best part of 300 notes for one!
But with it disconnected the fault has gone.
What's this unit all about then?, and is it only emissions related and not really needed running?

Correct the secondary air pump is for emissions...it pumps air into the intake to help warm the cat up quicker.

The fault code you have is quite common I get it all the time at work, have a look on the rear of the head (slightly to the left near the bulkhead of the car) there should be a valve with a vacuum tube going to it...make sure this tube is ok because if its leaking it can throw that fault code.

Let me know if that helps

cheers for the reply, will investigate and let you know,

well, pretty much all the vac pipes have been replaced and the problem persisted, then he took the secondary air pump apart and it was full of water, how it got in there is not clear, perhaps a build up of condensation, perhaps from standing water? it's not been driven through any floods or anything?
Anyhow, with the pump disconnected the fault didn't reoccur, cleaned the pump out, put back fully connected and it's done over 1000 miles without the fault coming back, so hopefully that's it.

excellent news