I set two codes I haven't seen very much on the boards today. I haven't heard of our pre-cat O2 sensors failing much, so I was skeptical. Unfortunately there doesn't seem to be an easy way to bench test a wideband O2 sensor, so I'm hoping I've arrived at the right conclusion by eliminating all of the connectors/terminals en-route between the sensor and ECM. I probed both ends of each wire at the terminals with my multimeter and found 0 to .3 ohm resistance (which is negligible, because I see practically that much touching the meter's leads directly to one another). I didn't go so far as a "wiggle and tap test" along the harness, but I'm pretty confident it *just* needs a new sensor.
I pulled the sensor out to take a look, and it doesn't visibly appear fouled in any way.
Wish me luck! I'll update this thread with results later on in the week after I get the new sensor and install it.
For reference, here are the DTC definitions:
P2297
HO2S Performance During Decel Fuel Cut-Off Sensor 1
P2626
HO2S Pumping Current Trim Circuit Sensor 1