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2004 Sierra 1500 5.3
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3 Posts
Discussion Starter · #1 ·
This is not a comment of how to install knock sensors; rather, it's about what to do when you've done a good job of replacing them and your code (P0327 or P0332) keeps coming back.

I've just read through at least 120 other posts about this issue and can't find my answer. My truck is a 2004 GMC Sierra 1500 with the 5.3 engine. Mileage is about 150k. It all started when I pressure washed my engine. It threw a P0327 code. I took everything apart and, sure enough, the front bank 1 sensor had taken on some water, so the code made sense. I replaced both knock sensors and harness (using AC Delco parts) and also replaced the intake gaskets (Felpro metal type). When I got everything back together, I cleared the code but it came back within a day but this time it switched to P0332, the bank 2 sensor. I cleared it several times more but it kept coming back. I bought two more AC Delco knock sensors and changed them out again. This second time, I learned about the technical bulletin and so, I did the service bulletin and dammed up around each hole with RTV. I ohm'd the new wiring harness and it checked out so, I carefully put everything back together. I cleared the code and it came back within a day. I cleared it several more times but P0332 kept coming back. I might add that on this second set of knock sensors that I ohm tested them (99 or so....within specs) and AC Volt tested them....all good. Also, the truck sounds perfect, runs perfect, and mileage is very good.

I've scoured the internet looking for any other issues that might be causing this code to throw. I'm sharing this next part below in case it will help someone else who's having the same issue.

So, if you're like me and you've changed both sensors and harness with OEM parts, you've changed out the intake gaskets and, you're confident you have a good seal, here's some other things to look at or consider:
1) Check for anything loose (such as motor mounts, exhaust heat shields, etc.) that may be sending a false knocking that the sensor is picking up. I haven't found this on my truck but you might.
2) Check that the knock sensor properly grounds when installing them. This can be done by making sure any dirt, rust, corrosion is cleaned up down in the "hole" before you install it. A good clean surface will ensure a good ground.
3) Re-learning the ECM. Okay, I found one guy on YouTube who suggested this and it works for about 95% of the people like myself. Here's the link to his video: Secret to Fix Knock Sensor Issue - YouTube . Basically, what this video suggests is that once you've replaced the knock sensors and harness, you will clear the code and then "re-learn" your ECM by starting your truck and revving the engine to 5000 rpms for 3-5 seconds a couple of times. This will re-learn the ECM to know what is the new normal rpm range and the vibrations associated with that. I tried this and it did work longer than any other time prior. To be fair, my tachometer quit a long time ago and I'm not sure I took it to 5000 rpm's or not. I cleared the code last night and revved the engine pretty hard so I'm hoping it takes this time. I can report back tomorrow evening because I will be driving at least 100 miles tomorrow. I am hoping this procedure works because there are a ton of people in the comments that swear by it! My fingers are crossed! This procedure does make sense but I can't find any bulletins or info about "re-learning the ECM".

I hope this helps someone who's as aggravated as I have been. If someone can add to the list of possible solutions, I would love to read your comments. If you've found something that fixed your codes from coming back, please reply with your experience.
 

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1999 Silverado ECSB 6.0
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2,346 Posts
I have never heard of this re-learning of the ECM.

I am almost certain that my code was something slamming against the frame or somethin like that. I would only get knock whenever I hit a hole in the road. Never when just normally driving.
 

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2004 Sierra 1500 5.3
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3 Posts
Discussion Starter · #3 ·
This is not a comment of how to install knock sensors; rather, it's about what to do when you've done a good job of replacing them and your code (P0327 or P0332) keeps coming back.

I've just read through at least 120 other posts about this issue and can't find my answer. My truck is a 2004 GMC Sierra 1500 with the 5.3 engine. Mileage is about 150k. It all started when I pressure washed my engine. It threw a P0327 code. I took everything apart and, sure enough, the front bank 1 sensor had taken on some water, so the code made sense. I replaced both knock sensors and harness (using AC Delco parts) and also replaced the intake gaskets (Felpro metal type). When I got everything back together, I cleared the code but it came back within a day but this time it switched to P0332, the bank 2 sensor. I cleared it several times more but it kept coming back. I bought two more AC Delco knock sensors and changed them out again. This second time, I learned about the technical bulletin and so, I did the service bulletin and dammed up around each hole with RTV. I ohm'd the new wiring harness and it checked out so, I carefully put everything back together. I cleared the code and it came back within a day. I cleared it several more times but P0332 kept coming back. I might add that on this second set of knock sensors that I ohm tested them (99 or so....within specs) and AC Volt tested them....all good. Also, the truck sounds perfect, runs perfect, and mileage is very good.

I've scoured the internet looking for any other issues that might be causing this code to throw. I'm sharing this next part below in case it will help someone else who's having the same issue.

So, if you're like me and you've changed both sensors and harness with OEM parts, you've changed out the intake gaskets and, you're confident you have a good seal, here's some other things to look at or consider:
1) Check for anything loose (such as motor mounts, exhaust heat shields, etc.) that may be sending a false knocking that the sensor is picking up. I haven't found this on my truck but you might.
2) Check that the knock sensor properly grounds when installing them. This can be done by making sure any dirt, rust, corrosion is cleaned up down in the "hole" before you install it. A good clean surface will ensure a good ground.
3) Re-learning the ECM. Okay, I found one guy on YouTube who suggested this and it works for about 95% of the people like myself. Here's the link to his video: Secret to Fix Knock Sensor Issue - YouTube . Basically, what this video suggests is that once you've replaced the knock sensors and harness, you will clear the code and then "re-learn" your ECM by starting your truck and revving the engine to 5000 rpms for 3-5 seconds a couple of times. This will re-learn the ECM to know what is the new normal rpm range and the vibrations associated with that. I tried this and it did work longer than any other time prior. To be fair, my tachometer quit a long time ago and I'm not sure I took it to 5000 rpm's or not. I cleared the code last night and revved the engine pretty hard so I'm hoping it takes this time. I can report back tomorrow evening because I will be driving at least 100 miles tomorrow. I am hoping this procedure works because there are a ton of people in the comments that swear by it! My fingers are crossed! This procedure does make sense but I can't find any bulletins or info about "re-learning the ECM".

I hope this helps someone who's as aggravated as I have been. If someone can add to the list of possible solutions, I would love to read your comments. If you've found something that fixed your codes from coming back, please reply with your experience.
Quick update....
It's been three days since I did the last "relearn", have driven over 100 miles, and the code has NOT popped up! I'll try to report back in a week or so.
 

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Registered
2004 Sierra 1500 5.3
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3 Posts
Discussion Starter · #4 ·
I have never heard of this re-learning of the ECM.

I am almost certain that my code was something slamming against the frame or somethin like that. I would only get knock whenever I hit a hole in the road. Never when just normally driving.
I think that's very important if you can notice a trend of when the code shows up. All the best!
 

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2001 5.3 silverado extra cab
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13 Posts
I am stuck in the same boat, new GM parts, continuous codes. I do have incrediblely loud fuel injectors, but have been reassured by mechanics that this couldn’t possibly be the cause. I don’t believe them.
here is the one question no one has ever answered.: what happens when the sensor reacts to a knock, ? Does the voltage DROP? I am wondering if the constant audible rattle of the fuel injectors are setting off the knock sensors, causing a voltage drop??? Mine ohm out at 99.7, all new ac DELCO GM OEM parts …other than that, anyone have a wiring diagram that traces knock sensors to ECU? My error codes are low voltage, both knock sensors.
 
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