Water at blue pcm harness 06 sierra 5.3 139k miles

Mando Ruiz · June 3, 2018

Newbie here, so be nice ?

Bought the truck from a private party 3 weeks ago. Seems like the previous owner decided to wash the engine (big mistake) Truck was, and is running fine but getting knock sensor code and fans turn on when vehicle is parked. Searched online and a few people have had this issue. Followed the proper pcm removal and drying method. No corrosion whatsoever, just a bit of water. Plugged back in and cleared codes. 4 days later I jump on the frwy and ses light appears. Get home and check codes. Knock sensor and fan codes appear. I erase them and then out of nowhere fans are on again while truck is parked. Open up the pcm and again, there's water. Anyone else have this issue and found a solution? For now I dried it up and put dielectric grease all the way around the connector to hopefully keep water from seeping in. I even thought about putting the pcm in a plascti bag. Any ideas/suggestions? Like I said before, truck is running perfectly fine.

Supreme Pizza · June 3, 2018

Your knock sensors are sitting in a pool of water. Very common issue. It corrodes and shorts out the connector. Been there. Is it your front or rear senor that is throwing a code?

Your knock sensors are fine, but you need to fix the connector, where it attaches to the top of the sensor. The book (and the dealer) says that you need to pull the intake manifold, and replace the sensors and harness, and then use silicon sealer on the sensor boots. You don't need to do that. You can reach under the front of your intake manifold, and remove a large piece of foam, which is locking the moisture in. It was designed that way, to allow moisture in from a hose or pressure washer, but wont let it back out even with evaporation (you can guess why). Anyway, you can touch the front sensor with your hand, so hopefully that is the problem sensor. Buy a new sensor harness, and splice it in by re-routing the harness through the front of the manifold rather than the rear.

If your sensors are shot, and have to be changed, don't pull the manifold. Just thread the sensors into the threaded holes in the front of your cylinder heads, and hook up the new wiring harness. DO NOT buy cheap knock off sensors, they don't work. Get the good OEM ones. I have tried both. You need the OEMs for sure.

I have relocated countless knock sensors. It will not cause a problem. The engine metal transmits the info the sensor just fine, even if you bolt the sensors to the top of an intake manifold.

Edited June 3, 2018 by starman8tdc

Supreme Pizza · June 3, 2018

https://www.amazon.com/FOLCONROAD-Sensor-Harness-Silverado-Cadillac/dp/B07BXDFJ96/ref=sr_1_15?ie=UTF8&qid=1528062061&sr=8-15&keywords=chevy+5.3+knock+sensor+harness

Edited June 3, 2018 by starman8tdc

Supreme Pizza · June 3, 2018

Supreme Pizza · June 3, 2018

Supreme Pizza · June 3, 2018

DO NOT USE THESE:

https://www.amazon.com/Detonation-Sensor-Cadillac-Chevrolet-Pontiac/dp/B06XR8G9SR/ref=sr_1_1_sspa?ie=UTF8&qid=1528062431&sr=8-1-spons&keywords=chevy+5.3+knock+sensors&psc=1

THESE ARE WHAT YOU NEED:

https://www.amazon.com/ACDelco-213-3521-Original-Equipment-Detonation/dp/B000K02EDG/ref=sr_1_2?ie=UTF8&qid=1528062523&sr=8-2&keywords=chevy+5.3+knock+sensors+oem

Mando Ruiz · June 4, 2018

Your knock sensors are sitting in a pool of water. Very common issue. It corrodes and shorts out the connector. Been there. Is it your front or rear senor that is throwing a code?

Your knock sensors are fine, but you need to fix the connector, where it attaches to the top of the sensor. The book (and the dealer) says that you need to pull the intake manifold, and replace the sensors and harness, and then use silicon sealer on the sensor boots. You don't need to do that. You can reach under the front of your intake manifold, and remove a large piece of foam, which is locking the moisture in. It was designed that way, to allow moisture in from a hose or pressure washer, but wont let it back out even with evaporation (you can guess why). Anyway, you can touch the front sensor with your hand, so hopefully that is the problem sensor. Buy a new sensor harness, and splice it in by re-routing the harness through the front of the manifold rather than the rear.

If your sensors are shot, and have to be changed, don't pull the manifold. Just thread the sensors into the threaded holes in the front of your cylinder heads, and hook up the new wiring harness. DO NOT buy cheap knock off sensors, they don't work. Get the good OEM ones. I have tried both. You need the OEMs for sure.

I have relocated countless knock sensors. It will not cause a problem. The engine metal transmits the info the sensor just fine, even if you bolt the sensors to the top of an intake manifold.

So after some more fiddling with the connector I noticed all this buildup. Blew it all out and cleaned everything out real good. Hoping this was the problem. After I did this, the ses light turned off. Fingers crossed. I do have GM knock sensors, gm harness, felpro intake gasket, felpro throttle body gasket on their way. Will have the knock sensors replaced this week [emoji120]

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Supreme Pizza · June 4, 2018

That is a serious PCM problem. It should be resolved before any other repairs. Also, clear the codes after the repair, or get a fresh start.

Mando Ruiz · June 4, 2018

That is a serious PCM problem. It should be resolved before any other repairs. Also, clear the codes after the repair, or get a fresh start.

Resolved in what way? Change out the connector I assume? All the pins were still intact, just a bunch of water and some dielectric grease built up. Cleaned off everything real good, reinstalled the pcm and the truck is running fine with no ses light. I will keep monitoring the fan, but I believe that's what was causing the problems. I read that the bottom pins (those affected) are those of the fan and knock sensors. Is that the case?

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Supreme Pizza · June 4, 2018

If that was my rig, I would blow out both the male and female ends of the connection with compressed air. Then I would clean up the male ends with a wire brush, and the female end with a very small pipe cleaner. Then I would spray everything down and rinse with mass airflow sensor cleaner. Then I would thoroughly smother the area with dialectic grease.

You can not have that problem in that area. It is extremely bad. All of your computer information may be off.

Your computer may react to incorrect signals

Your computer may send incorrect signals

Any and all information from and to the computer could be corrupt or incorrect

It could break down at any time with no advanced warning

Electrical short could fry the computer or other circuits in the vehicle

Possible fire

Your truck has an arrow in its heart. Worry about broken bones and abrasions after you fix the heart problem.

Edited June 4, 2018 by starman8tdc

Mando Ruiz · June 8, 2018

If that was my rig, I would blow out both the male and female ends of the connection with compressed air. Then I would clean up the male ends with a wire brush, and the female end with a very small pipe cleaner. Then I would spray everything down and rinse with mass airflow sensor cleaner. Then I would thoroughly smother the area with dialectic grease.

You can not have that problem in that area. It is extremely bad. All of your computer information may be off.

Your computer may react to incorrect signals
Your computer may send incorrect signals
Any and all information from and to the computer could be corrupt or incorrect
It could break down at any time with no advanced warning
Electrical short could fry the computer or other circuits in the vehicle
Possible fire

Your truck has an arrow in its heart. Worry about broken bones and abrasions after you fix the heart problem.

So I took it apart on Sunday. Blew it out really good, sprayed it down with electronic cleaner. Cleaned up male and female ends with wire brush. Was running fine since then. Well today I noticed the fan was on again while truck was off. Disconnected again and voila, water again! Where the hell is water entering from?! I looked all over and nothing looks wet. Hasn't rained at all (I live in California) anyone have a clue how water gets in there? Please help! I'm about to burn this truck lol

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Supreme Pizza · June 8, 2018

Dialectic grease does not conduct electricity, so it can be used used to keep water out. See pic:

Edited June 8, 2018 by starman8tdc

Mando Ruiz · June 8, 2018

Dialectic grease does not conduct electricity, so it can be used used to keep water out. See pic:

I'd really like to know where water is coming in from. Dielectric grease will probably help, but I'd like to get to the bottom of it. I doubt I'm the only one having this issue.

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