abscate, thank you for your continued help with this! I'll look into the wiring for my '01 re. what else is connected and ensuring the O2 sensor has sufficient voltage.
I've also ordered another O2 sensor (Denso) despite the present one (Bosch) only being about a year old. At this point I'm OK with dropping another $100 on a potentially unneeded part for the potential reward of making this all go away without spending all my future weekends probing under the hood with the multimeter.
