Rear window leak

Jrodpic · October 20, 2020

https://static.nhtsa.gov/odi/tsbs/2020/MC-10171889-9999.pdf

Looking at the pictures from the service bulletin I am convinced it is caused by water running down the top gap of the spoiler. It is either getting in the holes or cracks on top of the window. I am willing to bet that if a gasket/weather stripping was put in to prevent water from getting in that gap it would fix the problem. Someone with a leak should try to measure the gap and use something like this. That’s one of the first things I am going to do once ours if finally delivered.

1/16”? 1/8”? 1/4”?

https://www.zoro.com/e-james-rubber-cord-neoprene-18-in-dia-10-ft-csneo-18-10/i/G7615781/?recommended=true

Loner88 · October 21, 2020

Mine is at the dealer now for this leak. They claim it's the 3rd brake light gasket. New seal is in but they are waiting for new, revised nuts to reinstall everything. Looking at a week before I get it back, maybe longer.

econometrics · October 21, 2020

2 hours ago, Loner88 said:

Mine is at the dealer now for this leak. They claim it's the 3rd brake light gasket. New seal is in but they are waiting for new, revised nuts to reinstall everything. Looking at a week before I get it back, maybe longer.

One of the many “reasons” all of us have heard in our multiple, unsuccessful trips to the shop to get the leak fixed. It’s almost like they know what BS line to give you to try and make you feel like they know it will work... when they know they’ll see you back in a month or two when it starts leaking again.

Transient · October 21, 2020

Instead of running to dealership first, has anybody considered having an independent leak test done? It would help you and the dealership figure out what's actually going on.

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Loner88 · October 21, 2020

7 hours ago, econometrics said:

One of the many “reasons” all of us have heard in our multiple, unsuccessful trips to the shop to get the leak fixed. It’s almost like they know what BS line to give you to try and make you feel like they know it will work... when they know they’ll see you back in a month or two when it starts leaking again.

I'm already sort of expecting that.

omegafiler · October 21, 2020

Concerned my new 2020 Sierra Denali 1500 may have this leak as I saw a small amount of water on the plastic portion of the passenger side C Pillar. I couldn't find signs of water anywhere else, but supposedly the dealer is looking at it.

Not exactly reassuring when they claimed to have not seen that issue yet, even after linking the TSB. If they can't find a problem, I'll try to reproduce myself. And get a case/complaint open with GMC directly. Given the repeat TSBs and countless owner reports, they clearly don't seem to be prioritizing the fix for their broken processes that's causing this to happen in the first place.

RadBrad · October 21, 2020

3 hours ago, omegafiler said:

Concerned my new 2020 Sierra Denali 1500 may have this leak as I saw a small amount of water on the plastic portion of the passenger side C Pillar. I couldn't find signs of water anywhere else, but supposedly the dealer is looking at it.

Not exactly reassuring when they claimed to have not seen that issue yet, even after linking the TSB. If they can't find a problem, I'll try to reproduce myself. And get a case/complaint open with GMC directly. Given the repeat TSBs and countless owner reports, they clearly don't seem to be prioritizing the fix for their broken processes that's causing this to happen in the first place.

I picked up my 2020 Denali on 8/30/20, its a 8/20 build. The first day I got it, it leaked from the passenger side rear window, onto the plastic you talk about, and down the window. I am 100% convinced that most of these power sliders leak on either side. I had a 2019 Silverado prior, but it had the dark headliner, so it wouldn't have been as easy to notice. This truck has the lighter color headliner, which is what made me notice the leak first, the wet headliner.

I took it in to the dealer, and they said "oh yeah" one of these. Not very comforting lol

Somewhat mutually I decided I didn't want them to tear apart the headliner, spoiler, rear window, caulk etc to basically not fix the leak for good. I think these repairs just put Band-Aids on if anything. It would be nice for the 2022 redesign to have a permanent fix for this.

I have had to have my truck towed, due to a battery that lost all its cranking amps (Wouldn't charge at all). I also am in the build date range for the valve spring issue, hope that doesn't happen!!

Good luck with your dealer.

omegafiler · October 21, 2020

59 minutes ago, RadBrad said:

I picked up my 2020 Denali on 8/30/20, its a 8/20 build. The first day I got it, it leaked from the passenger side rear window, onto the plastic you talk about, and down the window. I am 100% convinced that most of these power sliders leak on either side. I had a 2019 Silverado prior, but it had the dark headliner, so it wouldn't have been as easy to notice. This truck has the lighter color headliner, which is what made me notice the leak first, the wet headliner.

I took it in to the dealer, and they said "oh yeah" one of these. Not very comforting lol

Somewhat mutually I decided I didn't want them to tear apart the headliner, spoiler, rear window, caulk etc to basically not fix the leak for good. I think these repairs just put Band-Aids on if anything. It would be nice for the 2022 redesign to have a permanent fix for this.

I have had to have my truck towed, due to a battery that lost all its cranking amps (Wouldn't charge at all). I also am in the build date range for the valve spring issue, hope that doesn't happen!!

Good luck with your dealer.

Mine is an 8/16/20 Build, also light interior. More concerned that there wasn't exactly a lot of rain when I noticed this. Which was actually during the test drive, but thought somebody left a window open, until I saw this post (and related TSB's).

If they think they can fix it, I'll let them do what needs to be done and then just make sure they put it back together correctly. Assuming they even make an attempt.

Duramaxsky · October 21, 2020

I picked up my 2020 Denali on 8/30/20, its a 8/20 build. The first day I got it, it leaked from the passenger side rear window, onto the plastic you talk about, and down the window. I am 100% convinced that most of these power sliders leak on either side. I had a 2019 Silverado prior, but it had the dark headliner, so it wouldn't have been as easy to notice. This truck has the lighter color headliner, which is what made me notice the leak first, the wet headliner.
I took it in to the dealer, and they said "oh yeah" one of these. Not very comforting lol
Somewhat mutually I decided I didn't want them to tear apart the headliner, spoiler, rear window, caulk etc to basically not fix the leak for good. I think these repairs just put Band-Aids on if anything. It would be nice for the 2022 redesign to have a permanent fix for this.

I have had to have my truck towed, due to a battery that lost all its cranking amps (Wouldn't charge at all). I also am in the build date range for the valve spring issue, hope that doesn't happen!!

Good luck with your dealer.

What is the valve spring issue?

If you want to find the leak yourself there is an easy way. It will work unless the leak is under the spoiler where you can't get to it. Take trash bags and hang them behind the cab in front of the vent outlets. Tape them in place. Push folded fabric like a towel down between it and the bed to hold the plastic bag against the vent. Turn the fan on high. Spray soapy water where you suspect the leak is. You will get bubbles. With the vents blocked the fan will pressurize the cab.

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RadBrad · October 21, 2020

5 minutes ago, Duramaxsky said:

What is the valve spring issue?

If you want to find the leak yourself there is an easy way. It will work unless the leak is under the spoiler where you can't get to it. Take trash bags and hang them behind the cab in front of the vent outlets. Tape them in place. Push folded fabric like a towel down between it and the bed to hold the plastic bag against the vent. Turn the fan on high. Spray soapy water where you suspect the leak is. You will get bubbles. With the vents blocked the fan will pressurize the cab.

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Interesting Idea--thanks for the information!

Here is the thread on the valve spring issue

RadBrad · October 21, 2020

16 minutes ago, omegafiler said:

Mine is an 8/16/20 Build, also light interior. More concerned that there wasn't exactly a lot of rain when I noticed this. Which was actually during the test drive, but thought somebody left a window open, until I saw this post (and related TSB's).

If they think they can fix it, I'll let them do what needs to be done and then just make sure they put it back together correctly. Assuming they even make an attempt.

Let me know what comes of it...

JWOutdoors29 · October 21, 2020

Dropped my truck off at the dealer this morning. I did not get to talk to the service manager like I had hoped since I somewhat know him, but the advisor I talked to seemed to be familiar with the issue. They called about an hour ago and said they put a simulated shower over the rear of the truck and found a "seam" that was leaking. They re-sealed it and are letting it cure. Now they are addressing the headliner as the wet spot/stain is very fresh and hopefully not an actual set in stain yet. I'm personally hoping they can just clean it and not have to remove the headliner completely. They are going to call me tomorrow with results. Fingers crossed it is fixed, cleaned, and no further created problems

Loner88 · October 21, 2020

Got mine back today after 6 days. Was not the light leaking like advisor told me but indeed the window per my paperwork. Now I get to argue about the stains in my headliner that I was told would be fixed.

RE1 · October 21, 2020

Dear God.... How is this still happening? Does GM have no shame?

paui4m · October 21, 2020

6 hours ago, RadBrad said:

I picked up my 2020 Denali on 8/30/20, its a 8/20 build. The first day I got it, it leaked from the passenger side rear window, onto the plastic you talk about, and down the window. I am 100% convinced that most of these power sliders leak on either side. I had a 2019 Silverado prior, but it had the dark headliner, so it wouldn't have been as easy to notice. This truck has the lighter color headliner, which is what made me notice the leak first, the wet headliner.

I took it in to the dealer, and they said "oh yeah" one of these. Not very comforting lol

Somewhat mutually I decided I didn't want them to tear apart the headliner, spoiler, rear window, caulk etc to basically not fix the leak for good. I think these repairs just put Band-Aids on if anything. It would be nice for the 2022 redesign to have a permanent fix for this.

I have had to have my truck towed, due to a battery that lost all its cranking amps (Wouldn't charge at all). I also am in the build date range for the valve spring issue, hope that doesn't happen!!

Good luck with your dealer.