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HuckleberryHunt's avatar
Jan 16, 2019

Warning: Silverado and Denali owners - water leak

After what I just went through I thought I'd bring this to other's attention just in case:

My DW and I purchased a new 2016 Silverado 2500 crew cab in July of 2016. We've been mostly happy with it. The only major issue I've had was the power steering box went out shortly after I got it and it was replaced under warranty.
The following story is a bit long ,but please bear with me.

Over the Christmas holidays I found water along the lower door sill in the back seat. The way I found it was that I'd placed a jacket on the floor and when I picked it up it was half saturated with water. The carpet was mostly dry, so I thought one of my kids had left a window open or something. I cleaned it up and the week after I found the same issue. I pulled the plastic cowling off the bottom of the door sill and there was standing water in the channel that holds the electrical cords. Further investigation proved that the carpet padding on the drivers side from front to rear was completely saturated with water. Unless I'd pulled the plastic cowling off the door, I'd not have noticed the water as the carpet is black and the rubber floor mats showed no sign of moisture.
I called the local dealership to have it looked at. Of course it was the holidays, so had to wait a week to get seen, meanwhile I still had to drive the vehicle. When I took it in, the dealer told me I was 300 miles over warranty (36K cap) and I'd have to authorize up to 4 hours of labor for diagnosis. I argued that this has obviously been going on for a while due to the volume of water in the cab and that it was not out of warranty when I made the appointment a week ago. No sympathy. I was told to contact GM. Since I didn't want to pay someone $90/hr to find a water leak, I canceled the appointment and called GM as well as the dealership I purchased the vehicle from. I got the same answer from the original dealer as I did the one I made the service appointment with. GM opened a case and it took 3 days for them to call me back (which I missed) and another 2 days after that to contact me again. Their answer was to go pay to get it diagnosed and then they'd review. Not being the type to enjoy paying people to do what I can do myself, I went in search of the leak myself. My research indicated it could be the satellite antenna (apparently problematic), the sunroof (direct or indirect), a leaking windshield seal, a leaking third brake light, or the back window. After a few hours, none of these had proven to be leaking. Only after I'd completely removed the back seat did I find the issue. There are "pressure relief valves" (vents) in the back wall of the cab (one on each side) that allow the pressure in the cab to be released when the doors are shut and the window closed. They are a very simple affair that simply pops into a rectangular hole cut in the back of the cab (one on the passenger and one on the driver's side). The seal on this item does not sit tight against the metal and the whole assembly was loose and rattled around when jiggled. Water would seep in around the edge and come in along the bottom of the assembly. Judging from he rate of water build up vs. how much was saturated into the floor of the cab, I'd say this has probably been going on for a couple years. Since everything was out, I checked the passenger side as well and it too was leaking, but not at the same rate as the driver's side. I found the culprit. Online research showed that this same part has been installed in multiple years (2001?-2019?) in the same fashion and it's a routine problem with the water leaking around the seal or the rubber rotting away and leaking. through the vent. In my opinion, it's a very poor design and a poor placement as water routinely runs across this assembly when it rains or when you wash the car.
At any rate, I'd run into another person the day before who suggested a service dept at a different dealer who they've had good luck with. I called them to explain the issue. The service manager I spoke to said that they'd just finished a truck with the same issue. He said it took a few hours to repair and four days to dry out. It's not feasible for me to be without my truck for a week. I told him I already found the problem and asked how much it was to repair. He estimated about $200 and would need it for a whole day for just the repair. I asked what they did and he said they add some sealant to the part and then leak test it after four hours to see if it worked. When I asked how much the part was I learned it was less than $40. No brainer there. I went and picked up the part and did it myself (very simple). I then spent a couple days with the carpets pulled back and a dehumidifier set up in the cab to dry out the carpet padding, which I wanted completely dry to avoid any mold/mildew. I've yet to reassemble the components, but hope that will go smoothly. Post project, I realized I did not need to purchase a new part...there was no difference between the old and new, so could have just removed/cleaned the old ones and added caulk before reinstalling, which is what I actually did on the passenger side, so would have saved me ~$35.
This project was not a "simple" one as much of the interior trim has to be removed to get to the problem part. I broke some of the snaps that secure the trim to the walls and will need to replace or fix those to put them back. I had a hard time finding "how to videos" on the web for my specific vehicle and this specific area. Therefore, unless you're really up to the challenge, it might be easier to have someone else do it. The nice thing was that I could still use my truck while I waited for the carpet/padding to dry. I'll try to link a picture of the problematic part, but have had varying degrees of success with this in the past, so no promises.

So, if you own a Silverado, try reaching your fingers under the back seat to the back of the cab and find the area below these vents to feel for moisture. The passenger side was leaking and I didn't even notice. Glad I checked.

Link to image of part:
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  • A little behind on the forums here, but how ironic is this topic? Just last night at work, I had an electrical issue w/ my semi (no left turn signals on tailer). Long story short, it was due to wire connectors INSIDE of the truck (2015 Freightliner) with the pins inside of the connector all green w/ corrosion!!! Mechanic said it was due to water/moisture inside of cab due to the vents on back wall as I asked hoe the H does water get inside of the connectors while it's on the back wall? Suffice to say, they didn't have a new harness, so had to switch out w/ a bute--ugh!
  • Yes to keeping the weep holes under the doors and the rocker panels too etc. Ultra important! The same goes for all makes of vehicles. If the holes become plugged for any reason or covered by debris either on the inside or the outside surfaces, water and/or condensation, pollutants, salt, etc WILL collect inside and rusting will result until rust thru occurs. Then it's too late!

    Of note is that so many before or after purchase new vehicles undercoater operators do not re-open the weep holes after spraying the undercoating material on and rusting happens from the inside out.


    Rusted thru vehicles have very poor resale value no mater the age or fine powertrain condition. It's your money rusting away and lost and so easily preventable! Takes about 10 minutes time at least once a year to be sure they are open.
  • My 2007 Tahoe’s right rear door was a water trap too, Dutch.

    “My research indicated it could be the satellite antenna.” And the 2015 Tahoe leaked like crazy via the satellite antenna, Huck.
  • Sounds like it would behoove all of us toblow out any weep holes during maint.
  • I've owned several new trucks and they all had these relief vents in the back of the cab. None of them ever leaked except for my 2015 Ram, third brake light.

    Nice write up! I hope I never have to deal with them.
  • philh wrote:
    Air Extractors (engineering term for the part) is generally not considered to be "wet". Water should not be getting there, you need to find the real leak, this is only on the path.


    I'm sorry, but have no idea what you're talking about. The leak was coming from around the faulty seal on this part. Of course water shouldn't be coming in there, but due to the faulty component and poor location, water did get in there. It's been sealed and hopefully rectified.
  • Air Extractors (engineering term for the part) is generally not considered to be "wet". Water should not be getting there, you need to find the real leak, this is only on the path.