New Oxygen Sensor Bad?
 

Few months ago noticed that I had an oxygen sensor that was failing/bad... no big deal so I replaced the unit. Went to get my car tested for emissions and found I had a burned out CEL. Replaced the light and found it was actually on.. again. It was intermittent which made me doubt the fact the oxygen sensor could be bad but who knows ...and the car was running a bit rough like it was a few months ago. I also figured O2 would be a hard fault as opposed to intermittent. I went to the gas station on my way to my buddys shop today and filled up ...then the CEL went away until 30 miles later when it tripped again.

Took it by my buddy at the audi dealer and found the same O2 was acting exactly as the previous one was. Voltage for the suspected bad one is way off from the others and i see it leaning out as the other bank fattens up (assumption from diag log). For the sake of eliminating things like MAF and who knows what I swapped the two pre-cat O2's plugs that are conveniently located on/by the fuel rail. Sure enough the problem moved to the other bank since I technically moved the sensor so at this point im quite confident the issue is completely isolated to the sensor (i think).

What I cant seem to wrap my mind around is that I had just replaced this sensor (NTK) so it seems odd that it would fail.

Also my bmw service manual here is kind enough to say "Voltage at idle .... 0.2 to 0.8 VDC fluctuating" which seems sort of broad. The "bad" sensor is hovering around .3-.5 and im throwing the CEL.

sorry for the bad pic especially if its not even necessary but you can see Bank2 Sensor1 is way off from the others.

http://forums.pelicanparts.com/uploa...1141780974.jpg

Did you replace the O2 sensor with a generic? I also was throwing O2 codes, replaced the original with an generic and ended up with some weird problems plus throwing the odd code. A year later I replaced it with a BMW sensor and all has been well since.

Tim

NTK which is OEM as far as I can tell. I guess I could try a Bosch.

replaced the sensor with another NTK (group buy cant pass it up) and my CEL hasnt cleared after a week of driving. i plan on taking it back by my buddys shop to see if we have the same results but im starting to think it might be something more related to a leak in the intake or some sort of vacuum leak.

Check the vacumm hose between your fuel pressure regulator and throttle body.

im doing trans mounts on my car this week so ill take a look at it when im down there crawling around

pulled the vacuum line put a meter on it while the car was running and i was getting 19si and likewise i was able to pump some pressure going to the fpr and it was holding it.

im thinking i might just take it to a dealer to diagnosis since its probably a vacuum leak somewhere...

I cleared out the CEL and it hasnt come back yet but still the voltage reads much lower on that sensor