Thanks! I had swapped out the related 10A fuse already (though the old one looked fine), and I doubt the Engine Main relay is faulty, given that I doubt the ECM and fuel injectors are having problems, but I have a spare of that relay, so I might just swap it to cover my bases.

I took a look at the O2 sensor's voltage readings over the OBDII reader, and it was reading a voltage of "--V", and no indication of it actually giving out a proper reading. Looks like I got a dud, so I'll get a replacement.