Will it hurt my engine if i dont replace my knock sensor

The pcm uses the knock sensor to monitor for engine knocking, and adjusts ignition timing based on this. If there is no knock sensor present, you will wind up with a hard fault that will keep the check engine lamp on continuously. Also, the truck will go into a more conservative driving mode to prevent knocking.
The knock sensor for a frontier is not terribly expensive, but it is a pain to access on nissan v6s, under the intake manifold

I would go with the engine being bad.
A knock sensor only sends a signal to the engine computer when there is a vibration or noise like a spark knock. The computer then adjusts spark timing to compensate.
If the engine is knocking such as a bearing knock, the sensor will be activated.

It will not pass inspection.
P0325 NISSAN - Knock Sensor Circuit Malfunction http://engine-codes.com/p0325_nissan.htmlForum CodePossible causes- Faulty knock sensor
- Knock sensor circuit short to ground
- Knock sensor circuit short to power
- Knock sensor circuit open
- Faulty Engine Control Module (ECM) Tech notes Very common problem with Nissan vehicles. Replacing the knock sensor usually takes care of the problem.

Check the wiring harnesses for bare or brittle spots. If none are found replace the spark plugs, all of them and spark plug wires. I know these are still fairly new but that is the next step. If you have over 60,000 miles on the vehicle it could be an issue with the timing chain but my experience tells me replace the crank Position sensor first if none of the other steps yield any results. Because these vehicles come with the power train warranties they do you can't really trust the Dealer Mechanics because they will do anything they can to prolong this to get the vehicle out of warranty.

dont worry about it. will not harm your vehicle if you dont replace it and it will not turn your check engine light on. you dont need to replace it realy, unles you realy want to waste your money.

IF YOU REPLACE SENSORS YOU HAVE TO ERASE PCM CODE TO TURN OFF CHECK ENGINE LIGHT.IF YOU DONT IT WILL KEEP LIGHTING UP.

this problem is very seldom the knock sensor, it can be the harness connector at the sensor or the engine has excessive knock which will set a code, u did not mention the particular code so hard to say, the location of the knock sensor is the lower section of the engine block, it is screwed into what would normally be a block drain plug, if u replace it u need to torque it to whatever the factory spec is or it can cause it throw another code..

I'd say the O2 sensor needs to be replaced

Yes, this is usually loose pistons. Boring the engine and replacing pistons would fix it. But, this won't hurt anything and lots of vehicles do it. Unless it really bothers you, I wouldn't even fix it. As long as the knock goes away after the engine warms up a little. Do you have any other problems could lead you to a different solution? Like check engine light or low oil pressure when cold?

It's the valley of the engine underneath the intake manifold. It's about an $800 job because the top of the engine has to come off. However, unless you have a supercharged xterra it shouldn't effect performance. Also, the knock sensor will not trip the check engine light, as it does not indicate a primary problem, so if your light is on you should have another code that should be fixed first.