My Truck Stinks (usually after rain)

[windsurfnut]

2022 GMC Sierra AT4

My truck has developed a musty smell, wet dog, gym bag.. whatever you want to call it.  Its exceptionally bad when closed up and in the sun.  I think, but not convinced, its worse after rainfall.

I have not found any wet/dampness anywhere in the cab or surface of carpets.  Nothing is wet along the back wall under the window.  There is no sign of water (yet) to be found.

I have replaced my cabin filter and done the lysol trick.  I thought that his maybe had solved it, but a heavy rain last night peaked the smell again.

 

Since I can find no dampness in the truck, I'm really struggling to find the source.

[SteveP45]

Did you buy the truck new or used?  If used how certain are you the truck was not subject to flooding with the previous owner….
 

What part of the country are you in?

 

Is the a/c condensate hose draining when you are running the a/c..  make sure it is not plugged.

 

Household ammonia is a great deodorizer.   Leave a small bowl or container sitting on the floor board overnight (be careful not to spill any).

 

cabin air filters only clean the air when the vehicle a/c or heating system is running.

[windsurfnut]

Bought new.  I'm in Toronto, Ontario, Canada.  

I am going to confirm the drain hose is not plugged.  I have typically seen water on driveway, but I'll make sure there its clear.

[KARNUT]

If you constantly run the AC in recirculating mode that can cause a musty smell.

[windsurfnut]

Just now, KARNUT said:

If you constantly run the AC in recirculating mode that can cause a musty smell.

I do not use that mode ever.  It may use it in AUTO, but I never manually engage it.  

[tjonesdfw]

Have had the same issue in our 2021 Denali for years.  Had the rear window re-seal TSB performed once, and recently had the entire power rear sliding window replaced, and it still smells like this after rain.  Condensate line doesn't appear to be plugged, and not finding wet carpet anywhere either.  Clearly something is collecting water and allowing it to sit though.  

[windsurfnut]

Ya, I don't want to start pulling panels and carpet up without some confidence I'm looking in the right places.  

[Bikerjon]

1 hour ago, windsurfnut said:

Ya, I don't want to start pulling panels and carpet up without some confidence I'm looking in the right places.  

Look carefully along the headliner above the rear window. Some of these trucks leaked above the high mount stoplight. Maybe check for wetness there after a heavy rain or a carwash.

[windsurfnut]

We've had some heavy rain and I have no signs on the headliner.  I popped off the door trim and reached under the carpet at all 4 footwells and all was dry.  Reaching around the rear seats, all dry.

 

I'm searching for the AC drain with no luck.  WIth AC running I am getting water dripping out from under the vehicle in multiple areas.  Firewall liner is wet behind right front tire wheel well liner. Water is certainly exiting, but I cannot locate the drain too fish a line it and see if its partially clogged. Any guidance in locating the drain would be helpful

[BIGDOGx]

I mean just keeping it simple stupid, did you try changing out the cabin filter yet? 

[windsurfnut]

Yep - First thing I did.

[Jay P]

Found this pic, it may help. Supposed to be a 22 Sierra.

Edited September 25, 2025 by Jay P

[2016 Sierra Owner]

Only 2 things I could think of with this.

1) Do you have a sun roof? Maybe all of the water is not draining out every time.  

2) The drain holes in the bottom of the doors could be clogged and let water collect in the door. 

[jore2019]

On 10/3/2025 at 6:55 AM, 2016 Sierra Owner said:

Only 2 things I could think of with this.

1) Do you have a sun roof? Maybe all of the water is not draining out every time.  

2) The drain holes in the bottom of the doors could be clogged and let water collect in the door. 

 

 

I have a 2022 Silverado LTD with the 3.0L Duramax and mine has a moldy smell also after it rains. I've brought it to the dealership and they could not find a leak. The only area I have not confirmed is clear is the A/C drains. This is a frustrating mystery I would like to solve. I love the truck otherwise.

 

Did you have any luck getting rid of the smell? 

 

[windsurfnut]

Nope, got cold here.  Once summer comes its bound to be back though.