Ok
I see you have an ohm meter, so...

Get a reading across blu sensor at normal running coolant temp.
Also get a reading on the single wire sensor [ temp gauge sender] to check the gauge reading accuracy.

Here is that comparison between the sensor and the gauge reading

OHM 110 = 60C
67 = 80C
38 = 100C

I have a 38 ohm resistor made up on a plug /harness in my tool box to check the gauge ..by just subbing the 38 ohms for the sender , the gauge should read 100C. Or use one of the other values from the chart.

Also, do you have a resistor bridging the connector to the blu sensor ??? Many guys do this to lower the cut-in temp of that sensor for high fan, but that will not allow default fuction test to be used as ACC panel will still see R value of that resistor even when the connector is unplugged from the sensor.