You know the story, your check engine light comes on and when you scan it, you see code P0332 which is related to the knock sensor circuit. This code is on a 2005 GMC Sierra w/ a 6.0L engine, and was set twice.
A knock sensor creates a voltage signal based on the vibrations caused by detonation. When spark KNOCK occurs, the voltage signal changes letting the computer know to retard timing (causing it to fire later). Because the best point at which to ignite the fuel/air mixture is just before pinking occurs, it is inevitable that sometimes knock will occur trying to reach that optimal point.
Back before scopes were necessary for accurately diagnosing sensors, “old timers” used to simply take a hammer and lightly tap next to the knock sensor and listen for engine RPM change – remember, knock sensors send a voltage signal based off of vibrations, or the change thereof. This is still a good indicator when diagnosing a possible bad knock sensor. Plus, the 4.8L, 5.3L, and 6.0L were notorious for allowing the rear knock sensor to begin filling with moisture, causing it to fail.
Begin by disconnecting the negative battery cable, and removing the plastic beauty cover (8mm) and hold down plate (10mm) under the back of it. Then, remove the air housing tube (8mm) that runs from the throttle body to the air filter box. Next, since I don’t like opening the coolant system, I remove the connector, three nuts (10mm), and two lower studs (E5 inverted torx) of the throttle body and lay it forward without disconnecting the coolant hoses running into the bottom of it.
Next, remove the two vacuum lines from the upper intake along with the connector to the evap. solenoid and tube (the back of the tube disconnects from behind the left rear of the engine). Then move on to disconnecting the eight fuel injectors, the two bulk head connectors located roughly halfway back on the inner side of the cylinder heads, the wire loom hold down nut toward the front of the upper intake, the fuel injector harness plastic clips that run down the side of the upper intake, the knock sensor harness connector attached to the upper intake toward the left rear, etc.
Once the above is completed, I take a bungee cord and pull the large wiring looms out of my way. Next, place a rag under the fuel line connection and disconnect the fuel line using a fuel line disconnect tool. After that, blow away any remaining debris one more time before removing the ten upper intake bots (8mm). Now, lift out the upper intake.
With the upper intake off, try to drain the remaining fuel in the fuel rail to keep it from randomly pouring out. I use intake or brake cleaner to thoroughly wipe out and clean the ports and area where the throttle body attaches. After cleaning it, blow out the intake and then attach the new upper intake gaskets to it, then set it aside.
Next, use a shop-vac to remove debris that might have fallen into the cylinder heads along with any lying on the lower intake plate. Remove the knock sensor cover grommets and wiring harness. Then, remove both knock sensors (7/8″).
As you can tell by the pic, the rear knock sensor is heavily corroded. Next, clean the cylinder head mating surfaces , lower intake plate, and knock sensor holes making sure to remove ANY debris that might have fallen into the cylinder head ports (I like to use brake cleaner).
Replace both knock sensors making sure to torque them to 15 ft. lbs., and then install the knock sensor harness and grommets. The harness I used sealed the holes so tight that I didn’t waste my time adding a bead of sealant along the front of the grommets as a water dam.
You’re on the downhill side now! Place the upper intake back onto the engine and torque the bolts in the pattern shown below. Make sure to torque the 1st pass at 44 in. lbs., and the 2nd pass at 89 in. lbs.
At this point, being re-assembling all components in the reverse order you took them apart. REMEMBER to thoroughly clean your throttle body and install a new throttle body gasket before re-attaching it to the upper intake. Also, make sure to attach your new knock sensor wiring harness connector to the upper intake before connecting it.
Re-attach your negative battery cable, make one last check to ensure everything is torqued and/or connected, and then fire your engine up and take it for a test drive!
It feels good not seeing the check engine light on! Congratulations, you just saved yourself money and learned how to do it yourself!