I just bought my first Audi! It is a 2002 S6 and is replacing my BMW E34. I've only had it for a few days and the check engine light came on. It is giving me code P0155 which appears to be the bank 2, sensor 1 O2 sensor. Could someone tell me which sensor this is and the easiest way to access it? Thanks!
I have the 4.2L V8. (Do 02 S6's come with anything else).

 

One more thing to note. I checked the oil level and it is over the maximum level. Would this be the cause for the failure of the sensor?

 

Wilkommen to the forums!
bank 2 sensor 1 is on the driver's side before the cat. Not 100% sure on the 4.2 exactly how best to get a wrench on it but if it is anything like my 2.7T is requires some interesting use of tools, creativity and flexibility on your part.

too much oil is probably not a good idea, unfortunately may or may not be the source of your sensor malfunction. be sure to check that your oil isn't contaminated (coolant). a sign of a problem (leaky oil cooler, best case. head gasket, worst case).

good luck

 

Thanks! Got a new sensor. I'll try putting it in tonight. Oil looks clean so I should be OK there.

 

good deal

report back your experiences with getting it changed out. I'm always interested in how different people get at the pre-cat sensors.

good luck

 

Didn't get it changed out. I couldn't even find it. The sensors after the cat are easy enough to find. I followed the exhaust back the the engine but didn't see anything, then I spent some time looking around under the hood... nothing. Any other advice?
Thanks

 

Can't seem to find a good DIY with pics for you. I will keep looking but in the meantime, from what I remember about seeing some other DIYs for the pre-cat O2 sensors, the easiest (relative) way to get at them is from under the hood.

the sensors should be located on the upper part of the downpipe, where it comes off the exhaust manifold

good luck

 

Got it swapped out. The sensor is easy to find once I removed the coolant overflow tank (see 1st pic). It was fairly easy to remove with the right tools. I put an offset O2 socket on the sensor then I could put an extension (actually 2 extensions: a 12" and a 6") into the socket from the top, turn with a ratchet and it was loose! The connector was right against the firewall and easy to access as well once the coolant tank was moved off to the side. Thanks for the help! The check engine light turned off on its own the second time I went for a drive--right about when the odometer hit a 100 mile increment--is this when the computer checks the sensors?