Temp sensor needs to be replaced

Why ? Temp gauge not working , cooling fans not working ? Is the check engine light lit an you have a coolant temp. sensor code ? The coolant temp. sensor is a input to the PCM/ECM - engine computer . If bad would turn on the check engine light. Trying to save you money an time replacing a sensor that may not need replacing .

My guess would be the temp sensor has failed or is unplugged.
What is the trouble code stored in the computer ?

get the code but i bet its the temp control sensor.

The first step is to determine whether the engine is actually running cold or if the engine computer just "thinks" it is. Your temperature gauge is controlled by the engine computer. I use an infrared thermometer directed at the base of the Engine Coolant Temp (ECT) sensor while watching the ECT sensor data on the computer to see if they match. This should be done before replacing ANY parts. You need to make sure that the ECT is not "lying" to your engine computer. Your vehicle is also equipped with a Cylinder Head Temperature (CHT) sensor to measure the the temperature at the cylinder head. (The ECT is located in the intake manifold.) These should read within 5 or 6 degrees from each other at all times. If it is determined that the sensors are all functioning properly, and the engine actually is running cold, then I would recommend getting a thermostat from the dealer. (I have had a few problems with aftermarket thermostats.)

your coolant temp depending on where you are has a lot to do with gas consumption so there for you might want to check your thermostate it could be letting to much coolant pass by at a time and its not keeping the proper temp in the engine do to your location

The "probable cause" is the "thermostat" is stuck open, not allowing the engine to reach operating temp (190-195f) . As for the sensors, obviously its working, but if its corroded, its leaking and needs to be replaced. Better hope the plug is ok or you will need to replace that also. Replace the thermostat. Stay away from autozone.

I would have the OBD II scanner clear the codes. Then if the code still pops up, I would have the coolant temperature sensor looked at.

The P0218 Code is primarily intended to indicate a faulty thermostat.
Have the thermostat replaced

Other possible causes that could trigger this code would be:
Low engine coolant level
faulty cooling fan
faulty coolant temperature sensor
faulty intake air temperature sensor

this is whats going on insufficient warm up time / low engine coolant /check coolant/ leaking or stuck thermostat or faulty tep sensor