knock sensor #2 on Gen4 5.3 V8
 

What do you need to take apart to get at KS #2 located on the passenger side of the engine? You can't get your hand in there.

2006 TB

I also saw on another post on this site something about the engine being "trained" by 15K miles, and knock sensor not necessary any more. That is incorrect. The engine continuously tries to find the sweet spot in timing for fuel efficiency and power as function of speed, load, temperature etc., and it uses the knock sensors to do that. With the knock sensor code set (the light is on), the computer justs employs a safe timing setting, which you can really feel when you are trying to pull a 5500 lb trailer up onto the Interstate. You can't simply ignore this..... as was suggested ..... FYI

OK here is the answer:

To remove: Jack the TB up, put safety jacks under, take the tire off. You can get to the bolt that holds the sensor on through the rubber flap at the rear of the wheel well. From underneath you can work the sensor down to where you can remove the electrical connector by sliding a small screw driver under the tab (see the new sensor to figure out).

To install new unit: Do not attach the wiring plug to the sensor. From under the vehicle, attach the sensor to one of those flexible claw grabbers, grabbing it by the electrical plug end. Carefully work it into position. The bolt will go into its hole a bit enough to stay there if you can cleverly bend the grabber such that it remains in place. From the flap in the rear of the wheel well, get the screw going until it is almost tight (the sensor will move but it will move with friction). Insert the electrical connector. Tighten to 180 inch-pounds.