Ozer, if you can find the connector for the temp sensor in the tank, see how many wires it has. I would expect 2 wires, but it could be more.

Do you have software or a scan tool that can "read" the current temperature of the DEF tank?

Does the DEF tank error light the SES/CEL/MIL and does it provide Freeze Frame data that may have the tank temperature when the error occurred?

Basic thermistor sensors are usually pretty reliable, the problem is most likely with bad solder joints on the sensor itself or wiring connections at the connector.

I am not sure why the DEF temperature is important, I do know that the DEF will slush or freeze and maybe the temp sensor main purpose is to prohibit the DEF from being used when it gets close to slush temperature?

Maybe the temp is also used to precisely adjust the DEF amount as well, I have no idea.
I assume the ideal position for the sensor is in the bottom of the tank so it stays submerged in the DEF?

But a working sensor near the DEF tank may be helpful and work out.

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2008 4.8i Black with Tabacco. Black Y-spoke wheels and shadowline trim.