Another cooling fan question

The cooling fan on my Jenn-Air JGS8850 comes on when the oven temp reaches 350 or more. The fan does not turn off until I turn the oven off, nor does it go off if I reset the temperature lower (to 275 for example). I am not getting an error codes and otherwise the oven works fine (It heats up appropriately). I have read several similar posts and based on those it would appear that I either need to change the temperature sensor or the front control panel assembly. Is there a specific test that I can run to isolate which is the problem? Thanks in advance!