mikegeezy

I need to know what the sensor is on my b16 it is located on the side of the head under the distributor it is the single wire connection one I know it has something to do with the coolant system but what? And do I have to have this hooked up? I ask because I bought this engine offline and got it today and was getting ready to put it in an noticed this sensor is broken off flush with the head so if I don't really need it I will leave it but if I do tnen I will have to try to get it out somehow. thanks in advance for your help..