Answer
Hi
Why are they suggesting the replacement of a Knock sensor?
Is the Check Engine light on?
If the check engine light is NOT on, there is NO reason I can think of to replace the sensor.
If it is on, I know the GenII engines (1999-2002) had a problem with water getting into the knock sensor mounting holes, and creating codes due to short circuits (Code P0332) for the REAR sensor ONLY. If you have a code P0327
that is for the front sensor ONLY. No need to replace them both. If you happen to have a code P0325, this code means that someone, somewhwers replaced the PCM (computer) and did not swap the Knoch Sensor Module into the new PCM computer.
Testing...Remove the intake manifold sight shield.
Disconnect the knock sensor 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 appropriate knock sensor using the DMM connected to battery ground.
Is the resistance of the knock sensor between 93 and 107k ohms.
If so the sensors are good
If not Connect the DMM between the appropriate knock sensor signal circuit on the sensor side and the engine block.
Set the DMM to the AC voltage scale.
Important: Do not tap on plastic engine components.
Tap on the engine block near the appropriate knock sensor while observing the signal indicated on the DMM.
Is any signal indicated on the DMM while tapping on the engine block near the knock sensor?
If so check all wires to PCM.
If not replace sensor(s) for the code set.
I hope this helps.
JUST advice from experience.
Good Luck
Pawl
It's been a while since anything was posted here, but I just went through the knock sensor fiasco and learned a lesson the hard way on my 2001 Suburban (225,000 miles). I purchased cheap sensors online for less than $20 for the pair. Installed them and had a SES light a couple days later. After much debate, I purchased a pair of OEM sensors for over $100. Before I put them in, I checked the $10 sensors with an oscilloscope (1st trace below). The voltage setting was on 200 mV/division, so the signal shown is about 1 V peak-to-peak. I then removed the sensor and replaced them with the OEM parts torqued to the same value. I then did the same test with the oscilloscope (2nd trace below). This time, however, the voltage setting is 2 V/division, so the signal is about 14 V peak-to-peak, more than 10 times higher than the cheap sensors. Both cheap sensors has about the same sensitivity (as did both OEM sensors), so this is very unlikely to be just two defective cheap sensors. They just do not have the performance of the OEM sensors. I am all for saving money when reasonable, but if you have to replace knock sensors, do yourself a favor and spring for OEM sensors.
I had both bank knock sensor codes (P0327 and P0332) within a day or so of installing the new cheap sensors. This was because their output was insufficient to keep the computer happy. I did measurements with the intake off so I could make a direct comparison between the new cheap sensors and the new OEM sensors under very similar conditions (same torque, tapping on the engine about the same, same temperature, etc.), thus I did not post any engine running traces. Note that the traces are open circuit measurements, going into the 1 Mohm input impedance of the scope through a 10X probe with the engine computer disconnected.well your post of these measurements , I would like to know what "your" codes were with the cheap sensors ?
also as you know the sensor output is dependent on engine noise. I would have liked to see a trace with more pulses not just the one pulse.
with all the pulses it gives a better understanding of the sensor ability to produce the signal based on engine noise.
O2 and the ks should be OEM because these will cause the PCM to throw codes and effect engine performance with other manufactures products. output will vary.
These KS fail because water enters in the front of the engine .The space opening between the upper and lower manifold GM used a sponge type material not water proof and over time disappears. the use of a sealer is used to close this opening also leave the rear open so any moisture that does get in can vent out.
