Where is the temperature sending unit on a 2007 Saturn Relay?

No, I doubt it, different year, but more importantly different models. But we can check. Haha. Nothing like!

https://fuse-box.info/saturn/saturn-ion-2003-2007-fuses-and-relay

https://fuse-box.info/saturn/saturn-vue-2001-2007-fuses-and-relay

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P0685 SATURN Engine Control Module Power Relay Control Circuit Open (autocodes.com)
P0685 ECM/PCM Power Relay Control Circuit Open (obd-codes.com)
Saturn VUE (2005 - 2007) - fuse box diagram - Auto Genius

Hope info helps

Fix your car right away, by clicking the link.
2005 2007 Saturn Relay Workshop Service Repair Manual Pdf

Check thermostat area housing etc.

Here's a link to your sensor. Repair Guides Coolant Temperature Sensor Removal Installation AutoZone... Here's what it look's like. Coolant Temperature Sensor 2007 Saturn Outlook 2WD 6 Cylinders 7 3 6L...

you are expecting the wrong temperature unit to control the fan. The temperature sender unit controls the temperature gauge and the temperature sensor unit controls the fan operation. It allows current to go to the ECM and when a pre set temperature is reached the ECM activates a relay and the fan starts . Two completely different units to do two different jobs so if it is doing what you say then there is a possibility that the wires are crossed or shorted.

It is in the fuel tank with the fuel tank sending unit.

On this website (link below) you find fuse box diagram and description for Saturn Relay (2006)

Saturn Relay 2006 2007 fuse box diagram Auto Genius

Either:the main fuse that controls this unit has blown orthe relay that controls this unit is blown ora circuit breaker for this unit has become stuck or
most likely this complete unit needs replacing as it has sufferred irreparable damage.

two things to check.... the sending unit and the relay for the fan.

I remember my dodge omni's fan didn't come on till near meltdown... but the temperature gauge never said it was that hot.