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Here is a print screen from 4 live data runs from my new OBD II scanner. All codes are clear now (started with a bunch of them back in October) except for P0420 Catalyst System Efficiency Below Threshold (Bank 1). I would like to eliminate the sensors before changing the catalytic converters. I don't want to change the catalytic converter if it does not need to be changed.

Please review the following data and tell me if anything points to the sensors. (If the sensors are okay, then I will finally have to accept that I need to change the bank 1 catalytic converter:


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Anyone able to make heads or tails of this data?
If it's the bank 1 cat that you're interested in, then the only sensors you need to look at are both Bank 1 O2 sensors. The upstream sensor should be switching back and forth between rich and lean, and the downstream should always be reading rich. If the downstream is switching just like the upstream (or starting to switch like the upstream), then the cat is bad.

Right now, one of my cats is getting so bad that I'm starting to hear pieces of the honeycomb rattling around. :p
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