Change out knock Senor in Nissan frontier 2000 now

underneath intake manifold between cylinder 1 and 2.

Why would you keep throwing parts at it and guessing what is wrong? Take it somewhere that has a scanner and see what is setting the check engine light. It could be a speed sensor, or anything for that matter. AutoZone and I am sure there are others will scan the code for free. If you live close to me I would scan it for you.

when you remove the intake you disconect many conector ck for the conector hat go tu transmision

that has nothing to do with knock sensor see if you have a vacuum hose off the trans I think they have one if not clean the electric plugs on the trans

Bypassing (hotwiring) the knock sensor will remove a signal the computer needs to operate. Unexpected results for sure , possible damage to the computer may result. Replacing the knock sensor is the best way.

You need a tune up or a new fuel filter or injectors cleaned

No you don't have to change the harness unless it is cracked, broken, or have burn marks.

no but the knock sensor does send a signal the ecm and it will ****** or advance the distributor timing

Either transmission oil pump is on its way out or reverse circuit is clogged , reverse shift solenoid is defective TCM may be defective , transmission range sensor begining to fail or manual shift valve and pressure regulator are defective.

Suggest taking the vehicle to a transmission repair shop they will diagnosis it and repair it.

Have you changed all the plugs to platinum and wires? My xterra was doing that and I changed all of them and now it runs great. Also, I changed the distribitor cap and rotor button.