the knock sensors have a rubber plug on top to keep out water, and seals the mounting hole. if the seal has failed the sensor hole will fill up w/water and cause the check engine light to come on. if you replace the sensors please silicone the rubber plugs on the top of them to protect the new sensors from sitting in standing water. a lot of times the knock sensor codes will come on after washing the engine... if this is the case the light may not come back on until water gets in the hole again..
this is the gm offical description and operation of the knock sensor
Knock Sensor (KS) System Description
Purpose
The knock sensor (KS) system enables the powertrain control module (PCM) to control the ignition timing advance for the best possible performance while protecting the engine from potentially damaging levels of detonation. The sensors in the KS system are used by the PCM as microphones to listen for abnormal engine noise that may indicate pre-ignition/detonation.
Sensor Description
There are 2 types of KS currently being used:
The broadband single wire sensor
The flat response 2-wire sensor
Both sensors use piezo-electric crystal technology to produce and send signals to the PCM. The amplitude and frequency of this signal will vary constantly depending on the vibration level within the engine. Flat response and broadband KS signals are processed differently by the PCM. The major differences are outlined below:
All broadband sensors use a single wire circuit. Some types of controllers will output a bias voltage on the KS signal wire. The bias voltage creates a voltage drop the PCM monitors and uses to help diagnose KS faults. The KS noise signal rides along this bias voltage, and due to the constantly fluctuating frequency and amplitude of the signal, will always be outside the bias voltage parameters. Another way to use the KS signals is for the PCM to learn the average normal noise output from the KS. The PCM uses this noise channel, and KS signal that rides along the noise channel, in much the same way as the bias voltage type does. Both systems will constantly monitor the KS system for a signal that is not present or falls within the noise channel.
The flat response KS uses a 2-wire circuit. The KS signal rides within a noise channel which is learned and output by the PCM. This noise channel is based upon the normal noise input from the KS and is known as background noise. As engine speed and load change, the noise channel upper and lower parameters will change to accommodate the KS signal, keeping the signal within the channel. If there is knock, the signal will range outside the noise channel and the PCM will reduce spark advance until the knock is reduced. These sensors are monitored in much the same way as the broadband sensors, except that an abnormal signal will stay outside of the noise channel or will not be present.
KS diagnostics can be calibrated to detect faults with the KS diagnostic inside the PCM, the KS wiring, the sensor output, or constant knocking from an outside influence such as a loose or damaged component. In order to determine which cylinders are knocking, the PCM uses KS signal information when the cylinders are near top dead center (TDC) of the firing stroke.
Subject: Audible Spark Knock (Detonation), MIL Illuminated, DTC P0332 Set (Replace Rear Bank Knock Sensor and RTV Area Around Sensor) #02-06-04-023A - (06/14/2002)
Models: 1998-2002 Chevrolet Camaro, Corvette
1998-2002 Pontiac Firebird
with 5.7L Engine (VIN G -- RPO LS1)
1999-2002 Chevrolet Silverado, Suburban, Tahoe
2002 Chevrolet Avalance
1999-2002 GMC Sierra, Yukon, Yukon XL
2002 Cadillac Escalade, Escalade EXT
with 4.8L, 5.3L or 6.0L Engine (VINs V, T, Z, N, U -- RPOs LR4, LM7, L59, LQ9, LQ4)
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This bulletin is being revised to add Cadillac Escalade and Cadillac Escalade EXT to the Models. Please discard Corporate Bulletin Number 02-06-04-023 (Section 6 -- Engine/Propulsion System).
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Condition
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.
Cause
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.
Correction
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.
Remove the intake manifold. Refer to the Intake Manifold Replacement procedure in the Engine Controls sub-section of the appropriate Service Manual.
Remove the wiring harness assembly from the knock sensor.
Remove the rear bank knock sensor.
Install the new rear bank knock sensor.
Tighten
Tighten the knock sensor to 20 N·m(15 lb ft).
Install the wiring harness assembly to the knock sensor.
Apply a bead of RTV silicone sealant approximately 9 mm (3/8 in) wide and 6 mm (1/4 in) high along the outside edge of the ridge on the engine block valley cover around the rear bank knock sensor. DO NOT form a complete circle. Leave the rear section open as shown.
From the underside of the intake manifold, completely remove the rear intake manifold seal (foam material).
Install the intake manifold. Refer to the Intake Manifold Replacement procedure in the Engine Controls sub-section of the appropriate Service Manual.
Parts Information
10456603
Sensor, Knock
DTC P0327 or P0332
Circuit Description
The knock sensors (KS) produce an AC signal under all engine operating conditions. The powertrain control module (PCM) calculates the average voltage range of each KS signal. If the KS system is operating normally, the PCM should monitor the KS voltage varying above and below calculated average voltage. If the PCM detects a KS 1 signal or a KS 2 signal voltage within the calculated average range, a DTC will be set. DTC P0327 refers to the front KS. DTC P0332 refers to the rear KS.
Conditions for Running the DTC
• DTCs P0117, P0118, P0121, P0122, P0123, P0125, P1114, P1115, P1121, P1122, or P1258, are not set.
• The minimum noise level must be learned. The minimum noise level is learned when the following conditions are met:
- The engine coolant temperature (ECT) must be greater than 60°C (140°F).
- The engine RPM is between 475-975 for 10 seconds.
• The engine speed is between 1,500-3,000 RPM.
• The manifold absolute pressure (Map) is less than 49 kPa.
• The engine coolant temperature (ECT) is more than 60°C (140°F).
• The throttle angle is more than 0 percent.
• The engine run time is more than 10 seconds.
• The ignition voltage is more than 10 volts.
Conditions for Setting the DTC
The PCM determines that this signal is less than the expected amount for more than 9 seconds.
Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
Conditions for Clearing the MIL/DTC
• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
• Clear the MIL and the DTC with a scan tool.
Diagnostic Aids
• Important: If the KS is dropped, the sensor must be replaced.
Inspect the KS for proper installation. A knock sensor that is loose or over torqued may cause the DTC to set.
• If DTCs P0327 and P0332 are set at the same time, inspect for poor connections at the KS harness jumper, located at the left rear side of the intake manifold.
• For an intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
This verifies the malfunction is present.
This test will isolate the KS from the rest of the circuit.
Tapping on the engine block will simulate an engine knock.
Step
Action
Values
Yes
No
Schematic Reference: Engine Controls Schematics
1
Did you perform the Diagnostic System Check-Engine Controls?
--
Go to Step 2
Go to Diagnostic System Check - Engine Controls
2
Important: If an engine knock can be heard, repair the engine mechanical condition before proceeding with this diagnostic.
Observe the Freeze Frame/Failure Records data for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the engine within the Conditions for Running the DTC as close to the Freeze Frame/Failure Records data that you observed.
Does the scan tool indicate that this diagnostic failed this ignition?
--
Go to Step 3
Go to Diagnostic Aids
3
Remove the intake manifold sight shield.
Disconnect the KS jumper harness connector located on the left side of the intake manifold.
Set the DMM to the 400K-ohm scale.
Measure the resistance of the affected KS using the DMM connected to battery ground.
Is the resistance of the KS within the specified range?
93K-107K ohms
Go to Step 4
Go to Step 6
4
Connect the DMM between the affected KS signal circuit on the sensor side and a good ground.
Set the DMM to the 400 mV AC hertz scale. Refer to Measuring Frequency in Wiring Systems.
Important: Do not tap on plastic engine components.
Tap on the engine block near the affected KS while observing the signal indicated on the DMM.
Is any signal indicated on the DMM while tapping on the engine block near the KS?
--
Go to Step 5
Go to Step 7
5
Disconnect the PCM connector. Refer to Powertrain Control Module (PCM) Replacement .
Test the KS signal circuit between the PCM and the KS jumper harness connector for the following:
- An open or high resistance
- A short to voltage
- A short to ground
Did you find and correct the condition?
--
Go to Step 12
Go to Step 9
6
Remove the intake manifold. Refer to Intake Manifold Replacement in Engine Mechanical 4.8L, 5.3L, 6.0L.
Test for an open, high resistance or a short to ground in the signal circuit between the KS jumper harness connector, located at the left side of the intake manifold and the KS connector.
Did you find and correct the condition?
--
Go to Step 12
Go to Step 7
7
Inspect the KS signal circuit for a poor connection at the affected KS. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If you find a poor connection repair the connector as necessary. Refer to Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 12
Go to Step 8
8
Replace the KS. Refer to Knock Sensor (KS) Replacement .
Did you complete the replacement?
--
Go to Step 12
--
9
Inspect the KS signal circuit for a poor connection at the KS jumper harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If you find a poor connection, repair the connector as necessary. Refer to Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 12
Go to Step 10
10
Inspect the KS signal circuit for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If you find a poor connection, repair the connector as necessary. Refer to Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 12
Go to Step 11
11
Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .
Is the action complete?
--
Go to Step 12
--
12
Use the scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass?
--
Go to Step 13
Go to Step 2
13
With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?
--
Go to Diagnostic Trouble Code (DTC) List
System OK
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i know this might be infomation overload but i was board....always ready to help 
38" swampers, 350 tbi, 14 bolt rear, 10 bolt front
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