AudiForYou's 2.7T

16524 - o2s b1 s2: no activity
17526 - o2s heating: b1 s2: open circuit - intermittent
17522 - o2s: b1 s2: internal resistance too high

Those are the codes.
Here are my questions:

1. Which of the 4 sensors is that?
2. If it's behind the cat, does it really need replacing, or can it be disregarded?
3. If I do replace it, is it worth it to replace all 4? How difficult is it to replace? I know the cables run down the firewall, but I am hoping there's no need to drop the engine or anything that crazy... Input please? Thanks!

Eric 2.7

you can remove the post cat sensors fairly easily, but I haven't done it. Get up on ramps and you can see the sensors right at the main cats.

The post cat sensors do not do anything for the ECU so, you could let it go.

I wouldn't replace a good 02 sensor since they are pricey.

FYI Bosch makes a universal that comes with a splice kit for about 1/2 the price of the OEM one ($70 vs $140).

ZIPPYGAS

I had o2 sensor fault codes also came on (ce light) last time it snowed and was cold. I had it cleared and it came back on a few days later I thought it was the 02 sensor but it was the coolant sensor (6 dollar part) the old ones were black and the new ones are green common failure. It could be going, My ce light came on both times. After they reset and changed the coolant sensor no 02 problems.

AudiForYou's 2.7T

I already have the green coolant temp sensor (changed it while swapping turbos)

AudiForYou's 2.7T

Thanks! Happen to have a part number or link for the universal sensor?

Eric 2.7

You can then get these about anywhere including you local auto parts store, but there are some cheap online options (specifics escape me right now, but a google search on the part number will work).

6ULDV8

The Bosch universal is a 15773 the factory number is 078 906 265N

AudiForYou's 2.7T

Any idea what that is?