Something must be wrong with the wiring harness going to my driver-side rear O2 connector, because the O2 sim there blinks, but my scan tool shows that the voltage never changes. The PCM is showing a code for that O2 sensor (bank 1 sensor 2). The passenger side sim voltage fluctuates normally as it should. If I swap the sims I get the same behavior, so it's definitely a harness issue.

If the PCM is getting a bad signal from a rear sensor, does it make any adjustments to the fuel trim? I would guess that it just uses the front O2's to evaluate the mixture, and then uses the rear O2's to make sure that the cats are working.

Any info? Thanks!