bighoss77

got a '01 2500HD with the 6.0L.... bought the truck with the check engine light on, ran great so i thought must be o2 sensor... had it checked and came back as knock sensors low input. so i changed both sensors and cleared code. light came back on a couple days later- same thing. so i read up some more and a few people mentioned the knock sensor harness could be bad. so i bought a harness from GM and warrantied out both sensors and replaced the harness and both sensors, and yes i cleaned out the sensor bores and sealed up the rubber boots. day later the light comes back on the for the same thing!!!! so ive just said fawk it! and its been like this for a few months. once in a blue moon the light will randomly go off a day or so, then pop back on... i have also noticed that if i am towing something heavy, like a camper or car tailer+car and im in the throttle on the interstate towing (since 6.0Ls are complete junk and have no power) the light will go off and stay off for the entire time im towing???! i need this fixed, becuase with the light on for this code, the computer retards the timing when on the throttle. also have a vortech supercharger waiting to go on and i definately dont want to throw it on with the codes showing up and messing with the timing... what to do???

06vortecmaxxx

iTrader: (2)

Did you use a torque wrench when you installed the sensors?

Chavette

iTrader: (6)

Unplug your knock sensor harness and check back to sensor to see that you got about 99 ohms each. If not close to that then your problem is harness and/or sensor. If close to above, then thats okay, but before I chased back to PCM, I would check the grounds thoroughly to the block. I once had a painted bracket in between ground and original location and even though the same bolt was going through it I got the knock sensor codes on a regular basis until I went back and grounded it directly to the block...then no more codes. If you can't find anything visual like break, loose connection, poor location, interference, etc. then I would pull pcm plugs and check with ohmeter the quality of the wire for rest of knock sensor circuit and the grounds to block. Not sure on your year but the ground you will be most interested should be on top of block or back of block/tranny mating area. A diagram of the circuit would be a big help. cheers

bighoss77

hmm okay ill check that ground... maybe i accidentaly broke it something while i had the upper off? and yes i torqued the sensors down to spec... ill have to ohm it out next chance i get... you guys gave me a good start, thanks!

bighoss77

OKAY, just tested the knock sensors with Ohm meter set on 200k and im getting perfect 100. on both sensors. i put the black wire to ground and red wire to each pin on the disconnected harness.... so its definately within spec which i read is 93-107. what do i do now? sorry for wanting to be spoon fed, but i cant find any other info besides one site that says something about if a pcm was replaced and someone didnt replace the knock sensor module in the pcm or something it would cuase the code?... bought truck used so i dont know.

i just tried running some octane boost and that did not turn the light off. once in a blue moon the light will go off for a few drive cycles then pop back on for months at a time. i do notice that when towing a heavy load most of the time the light will go off and stay off during towing conditions for some reason??? this make sense to anybody? im at my wits end here... sensors are ohm'ing out at perfect 100 on both, grounds look good, how do i test the harness going to the pcm? and what pins am i looking for on the pcm?

bighoss77

k. 93 octane does not solve the problem. so what about this... truck has 127k miles. i doubt the plugs have ever been changed. and i know for a fact the oxy sensors have never been changed becuase they are all surface rusted from this truck being on the coast of TX and then down in the FL keys for its entire life. im not getting a code for oxy sensors, but if they are getting "weak", as well as the plugs... could this potentially cause a CEL for the knock sensors low input?

Chavette

iTrader: (6)

IMO...low input KS code points to an electrical problem with that circuit. You checked the sensors to harness connector.....now you need to check back from disconnected harness to PCM points and then also the associated ground from PCM to engine. Get the schematics for your year/model and go after it again with with your ohm meter. Its annoying to find....sorry I know. Absolute worst case it is the completion of the circuit inside the PCM...though I am still thinking and hoping for your sake it is a ground wire issue.