Silverado Knock Sensors!

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by chevysr2004, Aug 6, 2007.

  1. chevysr2004

    chevysr2004 New Member

    I own a 2000 Silverado Z71 3dr ext cab 5.3L and my SES light came on. i checked and i am getting back code PO327 and PO332 (knock sensor circuit, low output). what is the easiest way to determine if the actual knock sensors need to be replaced or if its the knock sensor harness connector?
     
  2. Cableguy

    Cableguy Epic Member 5+ Years ROTM Winner 1000 Posts

  3. chevysr2004

    chevysr2004 New Member

    Thank you for the help. Anyone know how hard it is to get to the knock sensors and what tools are required. I'm pretty sure they are under the intake manifold, which doesn't sound like fun.
     
  4. Cableguy

    Cableguy Epic Member 5+ Years ROTM Winner 1000 Posts

    They are under there, but can't help you with tools. Sorry, Never done one on a 5.3L
     
  5. Oldbear

    Oldbear New Member

    There is a bullentin on that from GM (where I work) "0332" is a ground fault in the knock sensor wiring set off by moisture (there are two, but it won't tell you which one). Easy to get at - just remove the intake manifold, the sensors sit in a metal valley pan. Don't remove the pan, just the boots over the sensors and the sensors themselves. Put in new sensors, silicone between sensor and boot and wire and boot. Replace intake manifold, with new gaskets - your in there anyways... And your code should stay cleared.
     
  6. Oldbear

    Oldbear New Member

    And yes, you will need a tool to disconnect the fuel supply line from the fuel rail. But, other than that - nothing but an average tool kit. Ask your local GM/Chevy dealer for a few pictures of the intake manifold and knock sensor locations. Any nice parts guy will do it for you, maybe with a coffee or dounut... we parts guys work for these all the time
     
  7. unplugged

    unplugged Epic Member 5+ Years 1000 Posts

    Some info that might help:
    From: Allexperts
     
  8. sportnot

    sportnot New Member

    Hi, let me just add, I just replaced my knock sensor#2 two months ago, with silicone, and got an alarm again. It, and #1 had 100k-ohms, and 0.2V AC when knocked with hammer on block's side (suppose to be 5V, but digital meters never show spikes). I took off the upper manifold again, and found the #2 sensor was rusted again. I asume water is running down the wire, so $50 later (because I did not want to trust a rusted sensor even though it checked out) I replaced it and siliconed everything. A few things I learned: don't use anti-seize (the voltage is weak already), tighten to 10-15ft/lb, and double check that the well is clean of all rust and water (it is hard to see, unless you jump on your engine). Good Luck.
     
  9. Engineer1

    Engineer1 New Member

    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.
     

    Attached Files:

  10. j cat

    j cat Epic Member 5+ Years 1000 Posts


    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.
     

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