Mysterious Cabin Water Leak — Only After Rain, Not Car Wash

Hey everyone,

Hoping someone here has dealt with something similar — I’m chasing down a frustrating leak in my 2017 Tacoma.

What’s happening:

• After heavy or extended rain, parts of my floorboard get soaked, especially:
  • Front passenger side (under glove compartment)
    
    
  • Rear floor behind the front passenger seat
    
    
  • Under the back seat (mainly passenger side)
• The driver’s side floor stays completely dry.
  
  
• The driver’s seat belt feels wet when I pull it out to buckle up — not on the outside, but somewhere along the belt where it crosses my lap or stomach.
  
  
• The headliner is completely dry, no signs of staining, sagging, or moisture.
  
  
• After multiple rainy days, there’s a strong moldy smell inside the truck.

What it’s NOT:

• I go to the car wash 1–3 times a week, and I’ve never had water intrusion after a wash — this only happens after rain.
  
  
• I applied vinyl wrap around the roof channels and rear 3rd brake light — no change. I don’t think that’s where it’s coming from.

Photos attached show which areas are soaked and which stay dry.

Has anyone experienced a similar issue? Could this be a cowl drain, HVAC inlet, or door seal problem? Or maybe something behind the dash/firewall?

Really appreciate any advice before I start pulling things apart blindly.

Thanks in advance!

 

Primarily the water enters via roof mounts for the roof rack, rear vents, roof brake ligh, replaced windshield

 

You may find the answer here.

https://www.tacomaworld.com/threads/water-leaking-in-passenger-floorboard.750360/

 

If you’ve ever had your windshield replaced, they likely jacked the plastic shroud at the base of the windshield, and rain is now entering the intake air box for the climate controls. Check if your cabin air filter is wet next time it rains. This happened to me. If that plastic skirt that surrounds the wiper mechanisms isn’t fitted just right, water drains right into the air intake for your climate controls.

worth checking. If your cabin air filter is wet, that’s a good clue.

 

Thanks, Stocklocker. The windshield is OEM. I checked the cabin air filter, and it appears to be dry.

 

If the headliner is dry and it isn't affecting the driver's side, I would be looking at the door seal and the windshield seal on the passenger side. Car wash probably doesn't cause it because the volume of water and duration it is on the car is not long enough to pool up and flow through whatever spot it is leaking. Could also be the channel under the windshield starting to break down and leaking somewhere around the air intake (not through it).

 

Vents behind the rear seat . . Can’t see them unless you remove the plastic storage compartments . Vents only pop in maybe the weather strip on them is worn out . . I used silicone to seal them back up .

 

So, they recalled the rear stop light and those they ignored? Mine looks worn out, but I'm not sure if this is the only place water is entering.

 

Definitely seal the rear vents while you’re in there. Mine are less than 3 years old and the tabs that hold them in loosened up a bunch. I popped them out as far as I could and put sealant on them and it’s been good since.

 

How do you access the back? You've got to move the bed for that.

 

I put the sealant on the vent itself and snapped it back in. Also went back around it on the inside of the cab for good measure

 

did just about the same thing .

 

Thanks. Can you share what sealant you used?

 

use the larger tube and caulking gun .

 

Thank you, HelloFelix. I purchased this. Will report the results soon.

 

Well, the Permatex didn't work. I had to remove it, clean the area, and redo it using the GE Silicon suggested by HelloFelix. The caulking gun suggestion is also essential. After two rounds, I got it sealed. No more wet and smelly Tacoma. Thank you all!