" The PCM provides a 5v reference signal to the sensor. On a cold engine the resistance of the sensor is very high, so you get no voltage flow to ground. As the coolant warms, resistance decreases and more voltage flows to ground--but only IF the ground is in good condition. If it's corroded, the voltage will remain high.

You got a P0118 code. In order to set that, the PCM has to see 4.9 volts on the sensor input for more than 3 seconds. But it doesn't do this in a vacuum. It's also looking at throttle position, intake air temp, trans fluid temp, etc. In other words, the PCM knew the engine was warmed up when it saw high voltge. So, you either have a bad connection between the black wire at the sensor connector and the connector at the PCM. Or you have an open in the reference signal wire. Since you have temp gauge operation on the dash, you can rule out an open in the signal wire. But you cannot rule out a bad connection to ground.

Pulling the connector only confirms that the relay is working. You basically put the PCM into a default emergency state. It saw extremely high voltage--assumed that the sensor had failed or the ground wire had broken, and opted to be on the safe side and turn on the fans to prevent overheating. It doesn't tell us exactly how accurate the sensor is or what condition the wiring is.

You need to read the voltage on the reference wire under running conditions and compare the readings to the ACTUAL coolant temperature.

Here are some values: At a coolant temp of:
120°, voltage should be 4v
140°, voltage should be 3.6v
160°, voltage should be 3.20 v
180°, voltage should be 2.8v
210°, voltage should be 2.2v
220°, voltage should be 2.0v

If you see where I am heading here, you'll see that the difference between an engine that has JUST reached operating temp (180-190) and one that is overheating is only .8 of a volt.
I doubt that you can detect that difference in the needle on your dash. That's why I've been suggesting that you doing an actual voltage test instead of making an assumption that the sensor is good simply because the resistance changes. (An ohm test is NOT considered a reliable test--well, not as reliable as a voltage test, since voltage is what the PCM reads, not ohms.)

If you do see 2 volts and the coolant temp IS 220, the PCM should provide GROUND (not power) to the fan relay.

You're making a lot of assumptions about the condition of your wiring and I'm afraid you're heading right for a new PCM without doing some more advanced electrical testing. Just trying to save you some money here. It still may be a bad PCM, but I'd sure want to see some voltage readings to confirm that first.