Okay nevermind. Sensor 22 still reads in line with what sensor 12 reads, so I just reset the code. Drove around for 30 km and it never came back. Hopefully it was just some salt water grounding out the signal.
For the record, sensor 2-2 is the sensor up front underneath the oil filter. It turns out I hit a block of ice and bent the tail end of the sensor into almost a 90-degree bend. As it is only there to babysit the emissions system, I pulled an old sensor out of a Contour at the junkyard - total cost: $10.