1999 Saturn

It's the engine coolant temperature sensor and is about $9.00 at napa.. It is located on the engine block below the EGR valve area. Try a search for 'engine coolant temp sensor'

I might also mention that there is another one call the IAT or inpit ait temp.. it is the same part number and is located to the front and lower part of the air filter box. I might mention that I never had to replace that one though and also that NAPA does have the new sensor with the brass tip.