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Your truck's bank 2 knock sensor is a common failure, the 2 knock sensors as you know are under the intake, they both "sit" in a "cup", there is a problem with water intrusion into the rear B2 knock sensor.GM has a bulletin on the issue, after kncok sensor replacement a bead of silicone is placed around the rim of the "cup" to avoid this happening in the future.
Low voltage is usually a failure to produce enough voltage due to a faulty knock sensor, there could be a issue with the wiring to and from the knock sensor but very unlikley.
Some customers may comment on a mild to severe engine ping (commonly referred to as spark knock), usually worse during acceleration and/or an illuminated MIL. Upon investigation, the technician may find DTC P0332 set.
This condition may be the result of corrosion of the rear bank knock sensor due to water intrusion into the sensor cavity. This condition is more apparent on vehicles in which customers frequently wash the engine compartment.
Replace the rear bank knock sensor and build a dam (wall) around the sensor using RTV to divert water away from the sensor. Use the procedure and part number listed below.
Tighten Tighten the knock sensor to 20 N·m(15 lb ft).
Any more questions just ask
Is the resistance of the knock sensor within the specified range?
Important: Do not tap on plastic engine components.
Is any signal indicated on the DMM while tapping on the engine block near the knock sensor?