Checking the sensor for a leak is simple, just open your hood and look down at your lower radiator hose, find the sensor and you can see coolant remnants originating from the sides of the sensor and you should see a pool of coolant under the hose onto your lower engine panel.
Replacing the sensor can easily be accomplished by the average DIY guy, or gal. First step, make sure the cooling system is NOT hot! Open the reservoir aka (expansion tank) cap to relieve the pressure. Screw cap back on. (Putting cap back on is important if you don't want a mess) unplug connector, squeeze tabs and lift sensor out of radiator hose. Some coolant will come out but not much. Install new sensor (it comes with new O-Ring) and plug electrical connector into new sensor. Now you need to correct the coolant level (make sure not to overfill the system) Perform a cooling system pressure test to ensure no other leaks are present. Put on cap and clean off the spilled coolant with water. Your done!