mobaar

Got a CEL the other day, stopped by my local shop and they said I had two codes: 02 sensor and secondary air injection (or something like that). They reset them and said come back if the CEL comes back.

Well it came back today. Any ideas on cause? Something simple or gonna cost me my right kidney?

SnowZach

Could be a lot of things. For the V6, and 4 should be similar:

Something is wrong with the secondary injection, it pumps air into the cats to warm them up quick when you start the car cold. Here's some suggestions:

1. The pump isn't running, check fuses, pump. (That little approx1.5" hose that goes to the air intake box will be sucking when you fist start the car when it's cold (MUST BE COLD) if it's working right)

2. There is a vaccum actuator on each of the exhaust manifolds (or assumably one on the 4) It is a mushroom shaped thingy and it has a small vacuum line attached to it. Trace the vacuum line and make sure it's in good shape. Mine cracked and it's started throwing CEL's for secondary air injection. If it's a V6, there's a recall on those vacuum lines. Make sure you get it done.

The O2 sensor may be a result of the Secondary injection system not working. It's possible it's the other way around but the SAI is designed to heat the cat so it's working faster and the O2 may complain that the CAT isn't working because the SAI isn't working right.

There's a start... The exact errors on your codes would be a lot more helpful...

mobaar

I forget the exact codes though.

1.8T btw. Just had some other vac lines go bad, so maybe thats it. Thanks for the thoughts.

czand

iF IT IS A 2k LOOK AT THE KOMBI VALVE BEHIND HEAD

wrgum

Just wanted to say thanks for the old threads on the SAI and combi valve vacuum system. I've got a CEL w/ P0411 code. Turned out to be a busted vac line at the combi valve behind the cyl. head. Thanks all!

wrgum

2001 A4 1.8TQ