Measure the resistance across the sensor terminals - if open circuit them no good.
Resistance will vary depending on the type of material used in its manufacture.
If you get a reading then you can place it in a cup of water
with ice in it allow to settle and take a reading - that will be the 0 Degrees Centigrade or 32 F reading, next boiling water
will give 100 C or 212 F reading.
Manufacturer may give out what these reading should be.
Basically open circuit then get another.
If you are getting readings but believe they are not right then test your cables
up to the gauge for high resistance.