Knock sensors getting no power
Knock sensors getting no power Recently swapped out sensors and harness because I was throwing both codes. Found harness was smashed and frayed. Can’t get new sensors to get a signal from the ECM. Tried using a MM and pretty much narrowed down that no voltage is coming out of the ecm to the KS harness. Grounds seem ok, KS are at about 100k ohms... did I fry the pin out? Is the ecm bad? Ideas? Yes torqued to 15lbft
Last edited by vff_jeff; Sep 10, 2019 at 08:58 PM.
TECH Addict
Joined: Dec 2017
Posts: 2,183
Likes: 971
Yes and no.
Just like a microphone, it generates a tiny AC voltage, BUT ONLY when it's hearing a knock. The rest of the time it does NOTHING. You'd probably never ever see it on a multimeter. An O2 generates a small DC voltage OTOH, and it's more or less constant (assuming the oxygen content in the exh stream is more or less constant), so you can actually see and troubleshoot that to some extent with a DMM. A narrowband obviously generates some voltage when there's no oxygen there and none when there's not, with a pretty sharp cutoff; but regardless, if you create the right conditions in the exh stream, you can see it with a DMM. I doubt it would ever be possible to troubleshoot KSs with a DMM.
Just like a microphone, it generates a tiny AC voltage, BUT ONLY when it's hearing a knock. The rest of the time it does NOTHING. You'd probably never ever see it on a multimeter. An O2 generates a small DC voltage OTOH, and it's more or less constant (assuming the oxygen content in the exh stream is more or less constant), so you can actually see and troubleshoot that to some extent with a DMM. A narrowband obviously generates some voltage when there's no oxygen there and none when there's not, with a pretty sharp cutoff; but regardless, if you create the right conditions in the exh stream, you can see it with a DMM. I doubt it would ever be possible to troubleshoot KSs with a DMM.
So any ideas why it acts the same weather or not the knock sensor harness is plugged in? I reset code and monitor KR with interceptor and hptuners scanner. Within a few minutes it shows 3*knock constant no matter the rpm or load in or out of gear. Then after a while the CEL comes on and I get both knock sensor low voltage codes.
Same thing happens when I unplug the harness and start it. I’ve replaced sensors and harness and still no luck.
I read somewhere that the sensors should be getting 5volts or so from the ecm but maybe I heard wrong. Anyways... I can’t get the KR to stop pulling timing as if the sensors aren’t hooked up.
Same thing happens when I unplug the harness and start it. I’ve replaced sensors and harness and still no luck.
I read somewhere that the sensors should be getting 5volts or so from the ecm but maybe I heard wrong. Anyways... I can’t get the KR to stop pulling timing as if the sensors aren’t hooked up.
So any ideas why it acts the same weather or not the knock sensor harness is plugged in? I reset code and monitor KR with interceptor and hptuners scanner. Within a few minutes it shows 3*knock constant no matter the rpm or load in or out of gear. Then after a while the CEL comes on and I get both knock sensor low voltage codes.
Same thing happens when I unplug the harness and start it. I’ve replaced sensors and harness and still no luck.
I read somewhere that the sensors should be getting 5volts or so from the ecm but maybe I heard wrong. Anyways... I can’t get the KR to stop pulling timing as if the sensors aren’t hooked up.
Same thing happens when I unplug the harness and start it. I’ve replaced sensors and harness and still no luck.
I read somewhere that the sensors should be getting 5volts or so from the ecm but maybe I heard wrong. Anyways... I can’t get the KR to stop pulling timing as if the sensors aren’t hooked up.
it sounds like your KR sensors aren’t producing any voltage even under normal running conditions. This is the reason your timing is defaulting to safe retard setting. You already swapped the sensors and harness. So the next place to look would be any loose terminals. It’s entirely possible you got bad sensors out of the box too. There are ways to test them that involves a hammer and volt meter. Pretty easy to do. The last thing I would suspect is a bad PCM but I suppose that’s possible too. If you have a multi meter you can use the continuity setting to check the wiring from the sensor terminal all the way back to the PCM.
Trending Topics
Thanks I will give it a try. I know they were working for 8 months fine since I pulled the motor and rebuilt it. Then one day they quit working (throwing both KS low voltage codes.) I took off intake and discovered the harness was smashed and was shorting, so I replaced the sensors and the harness. I was worried maybe I fried the PCM.
Side note Im also having a vibration at 2700 rpms which I believe is the slave cylinder/ throwout bearing and maybe the pilot bearing as well. Ill test the continuity like you said and if that doesnt work Ill wait until after I pull the trans again sometime this week and fix the other issue. Maybe the slight vibration is setting off the sensors, but I think the issues are separate. Thanks for the help. Just seems like its one thing after the other. Just replaced the driveshaft because of a carrier bearing being bad and the rear end diff seal as well. I rebuilt the engine earlier this year by myself, which is also frustrating because all the parts were new.
Side note Im also having a vibration at 2700 rpms which I believe is the slave cylinder/ throwout bearing and maybe the pilot bearing as well. Ill test the continuity like you said and if that doesnt work Ill wait until after I pull the trans again sometime this week and fix the other issue. Maybe the slight vibration is setting off the sensors, but I think the issues are separate. Thanks for the help. Just seems like its one thing after the other. Just replaced the driveshaft because of a carrier bearing being bad and the rear end diff seal as well. I rebuilt the engine earlier this year by myself, which is also frustrating because all the parts were new.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
