I replaced the oil pressure sending unit on my 2000 honda se and next to it on the left is another sensor? or not sure what it is has wire connected but it appears it had a plastic cap that is broken off. Can some tell me what this is
and is it hard to replace

 

knock sensor, and you don't need to replace it unless you have a "check engine" light on with code P0325. plastic caps break, the world is an "imperfeck" place...

 

mine broke off too due to heat. Did not give a CEL but did impact the efficiency of my motor. Also as I have said before, I am **** about having everything mechanically work right on my car.

They are about 120 at autozone and it takes about 10 mins to replace.