There was a member here early on, username pmh013. She had an 03 AWD, and it ate catalytic converters. Hers would clog, resulting in performance issues, dramatic loss of power, odd shifting behavior like downshifting while driving easy on a flat highway, horrible mpgs (or l/kn, if you prefer) etc. I don't think they ever figured out what was causing it, and she didn't keep it long, especially compared to some here.
Aflegeal wrote: ↑Sun Nov 22, 2020 4:57 pm
Update: I watched the O2 sensors while driving and they seem to be behaving properly. Upstream sensor is jumping around a lot while downstream is staying around 0.5, oscillating slowly up and down a little, and reacting to throttle changes.
That sounds like it is supposed to. Usually the test for a 420 is if the front and rear O2 sensor readings are too similar, then the car assumes the cat isn't converting. I tend to blame all 420s on a bad cat, but yours seems to have failed way too early with uncharacteristic symptoms, making me wonder if it is really the culprit. If it is, then something else is likely a core cause, which, left uncorrected, could get expensive