Hi,
You have an issue with the sensor still. Either it is the sensor itself, wiring, or the control module. The temp should obviously not fluctuate very much but the -40 is an open circuit default. Meaning when the circuit goes open it defaults to -40. This is the most likely cause of you other issues.
Unfortunately I don't have a service manual for your vehicle so I can't provide you the wiring diagrams. However, the idea would be to check resistance in the sensor wiring then check for shorts to power and ground.
Once that is okay, the control module is most likely the issue.
https://www.2carpros.com/articles/how-to-check-wiring
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Friday, October 11th, 2019 AT 1:13 PM