I've noticed for a while now that my O2 sensors are behaving erratically. When I first start my car, the O2's read around 453 or so, which is normal. After ~30 seconds, they start reading normally (which in my case is 800-947) until the car is fully warmed up. At that point, both O2 sensors begin to send randon numbers to my Scanmaster. Has anyone else experienced this? Also, the car never leaves CELL 16 at an idle and CELL 18 under throttle, with an occasional CELL 17 under braking.
I would suspect the O2 sensor if it was just one that was acting that way, but they're both acing in concert.

 

Your O2s sound normal.

You might want to read this for some info about what your Scanmaster sees.

 

Thanks Shoebox. I remember reading that last fall when I first got the car, but didn't see how it fit at the time. Now I understand. When running rich, the values don't fluctuate much, hence the semi-consistent 800-900's. Once it gets close to the ideal 14.7:1 air: fuel ratio, the sensors work better and begin to read fluctuations more accurately, hence the "random values".

 

It also has a lot to do with the fact that the cats on the car operate best when they fluctuate from rich to lean. It has something to do with the design of the converters I believe. So the PCM is programmed to go back and forth from rich to lean. But overall, it averages a 14.7:1 AFR.

I've taken my car out and driven it a while, logging with Autotap. Then I take my log, add up all the o2 values for each pre-cat sensor (one total per side) then divide by the number of samples and I get a measurement right around .450 usually, and that's 14.7:1.