The Nissan Path

My "check engine" lite came on and the shop tells me I need to replace my knock sensor. I see from research that my '97 Pathfinder has 2.
Should both be replaced? How much time (approx) should be needed to do the task?
Does a bad knock sensor make my engine run rough....use too much fuel?
thanks for your help.

Some people relocate them to save $$$ in not pulling the intake manifolds. There is a youtube video, etc. Google Pathfinder +"knock sensor"

knock sensor code (p0325 - i think) wont trip your engine light.