Nissan Repair: knock sensor, 2004 nissan xterra, cold air intake

Question
How do I know if the knock sensor is going bad?
A friend of mine had to have his replaced due to
power loss.  Sometimes it is a struggle to keep
my truck up to speed especially on hills. It however does not seem to be knocking or anything
that would suggest a tune up.  It just seems very
sluggish.
2004 nissan xterra xe

Answer
Steven,

A 2004 should not need a knock sensor as of yet.  Also, if you buy a K&N airfilter you should gain some power.  Also, with the year and the miles you should not need a tuneup as of yet.  Other gains in horsepower are a cold air intake system along with a K&N cone filter and an aftermarket exhaust.  You should check the air in the tires as this willslow down a vehicle as you describe.  Run the pressure stated on the vehicle or up it by five pounds if you can live with the rougher ride.  Lastly, if you are hauling around a lot of heavy items in the vehicle this could cause the sluggishness on hills.  Oh, there are under drive pulleys for your Xterra too that can free up some horsepower too...