Yes, I read ALL of the posts, re-read my post, your previous suggestion was to measure an open circuit voltage, this is NOT the best way to check for voltage to a circuit. if there is high resistance in a connector or a fuse that has high resistance (yes, I've seen them) or any other high resistance in the circuit the open circuit voltage may be close to the battery voltage, but under load the voltage will drop, possibly to almost 0 volts.

Ideally, this test would be done with a load to ground and then measure the voltage across the load. This would verify the power side of the circuit. Unfortunately at this point we don't know what the output of the PCM is, it provides the ground side of the heater circuit and does this with a PWM. Since the sensor has been changed multiple times, I am assuming that the heater is okay (yes, possibly a bad assumption but I'm going with it for now.)
I just finished looking at the wiring diagram and all for sensors get their power from the same fuse, since only one sensor is failing it should be safe to assume that the power at the fuse is ok. The next step is to verify proper battery voltage to the sensor, after that its the wiring to the PCM and the PCM itself.