2008 Sierra Denali and drivers floorboard fills up with water with every rain. Checked all sunroof drains and everything working as it should. I poured water I to the sunroof 1 gallon at a time to completely fill it up and keep it full to try and find the leak and al drains work perfectly. Headliner never gets wet but even a small rain and the floorboard will have standing water. I can’t find any sign of the windshield leaking but that’s the only other think I can think of . Any ideas where else I should check?? I’m about to pull my hair out with this thing.

 

have you checked the 3rd brake light?

 

I sealed that first and moved on to the sunroof. The headliner never gets wet but the drivers side front will have standing water in it. I even thought it might be running down the side window and draining inside the truck but there isn’t any sign of it.

 

Pinch weld in the engine bay I think is a common spot.

Have you checked your windshield?

Check inside your door and make sure your wire boot is in correct.

 

I ran water down the lower half of the windshield and got water running on the inside near the kick panel. I pulled the cowl and found the sealant really cracked up and dry. I cleaned it with acetone and going to reseal it and check again. If this doesn’t fix it I’ll replace the windshield.

 

more than likely it is the cab vents on the back of the cab. sounds crazy, but with everything else you have tried. that is all that is left

 

If it isn’t wet in the backseat I highly doubt it