Car floor flooded while driving through a rain storm

The car floor was flooded, I mean it was really flooded (I removed several ounces of water after we return) on the rear driver side floor and the floor under the driver was wet when we drove through the rain storm for over 1 and half days recently. Since everywhere else is dry, I believe there must be a leak on the chassis floor. But how can I (or the shop) pinpoint the leak location? How can I get proof that the leak is fixed? I?d like to educate myself first before I take the car in for inspection and repair. Any suggestion is welcome. Thanks.

I’d more suspect either a plugged sunroof drain or a leak in the front windshield/front air vent area allowing water to collect on the floor. Unless you have a rust problem it’s unlikely to be a floor pan leak.

The front plastic cowl area below the windshield may have a cabin air filter. If the filter has never been changed debris may be blocking drainage and water could be spilling into the filter area.

Model year? mileage?

It’s highly unlikely that the water came up through the floor.

It’s more likely that it came in through the HVAC system, which has a drain that can be overcome by torrential rains. I’ve had water on the floor after driving through a very heavy rain storm. It came in through the heat vents.

Here’s the real problem: The padding under the carpet is now wet, and you cannot get the water out of the padding unless you remove the padding from the vehicle.

The padding is like a sponge, and it can hold an amazing amount of water. Mold and mildew will start to grow, and you will soon be able to smell it, unless it’s cold enough in your area to freeze the water. In that case you’ll start to smell it when spring arrives.

Shop vacs and/or carpet cleaners cannot extract the water from the padding underneath the carpet. You, or someone else, will have to lift the carpet, remove the padding, and allow it to dry outside the vehicle.

Thanks, but my car does not have a sunroof. We lived in the sun belt, not rust belt. As long as I know, there is no rust on the floor pan.

2004 model, less than 40,000 miles.

Thanks. But why it is unlikely the floor might have a loose/worn seal? Either way, it doesn’t sound like an easy job to fix.

Floor are stamped/welded pieces of steel, there aren’t much in the way of ‘seals’ to wear out. Really, only through rust or accident damage would I expect water to come through the pan…unless you drove through DEEP water - did you?

As Texases said, there just aren’t too many places where water can come through the floor, unless the vehicle is very old and rusty. Your car is not old enough to have a rusted floor pan.

I know it’s tempting to think the water came through the floor because you didn’t see it coming in, but that doesn’t mean it came through the floor.

The HVAC system is the most likely source. There are other possibilities, but holes in the floor are way down on the list of possibilities.

WAY down. Not likely. You need to focus elsewhere. I’m willing to bet your car does not have holes in the floor through which water comes in, and I’m not a gambling man.

I didn’t say it was easy to fix. I just told you the truth about the water and the padding.

You can take my word for it, or not, as you see fit.

When you start smelling the musty smell, you’ll remember what I told you.

Good luck.

No, we only drove on the wet pavement of the interstate with occasional water puddles. But nothing can be categorized as DEEP.

Thanks to texases, americar, Caddyman, mcparadise for your input. I appreciate that. I will do what needs to be done.

If you want to check for leaks that are higher up, you can use a squeeze bottle like a water bottle. Put car wash soap and water in the bottle. Idle the engine with all windows closed and vent fan on full speed. Squirt soapy water on edges of windshield and roof. Do it around the rear window too. Do it around the trunk.

If there are any leaks, soap bubbles will boil up like crazy. You would laugh if you saw this done on somebody else’s car.

2000 - 2005 GM “H Body” Cars, Of Which That LaSabre Is One, Can Have A Water Leak Problem Like The One You Describe.

Here’s the deal. Rain water enters car doors from the outside (through window slot openings) and ordinarily runs through the door and drains out the bottom of the door to the ground. Doors are designed to leak, just not inside the vehicle.

Most cars have a system for dealing with this and your Buick has a molded translucent plastic deflector that is sealed to the door with a strip of gooey black butyl sealer. This deflector is about the size and shape of each door’s vinyl interior trim panel (the big vinyl covered door interior that incorporates the arm rest) and sits between it and the steel door. You can’t see it until the trim panel is off.

Some of the 00-05 H-bodies have had the butyl loosen up at the bottom and allow water to leak inside the car. It seeps in along the bottom of the trim panel at the door nearest the wet floor.

Anyhow, that’s where I’d look, first. With a hose, have somebody rain (spray water) on that door from the ouside while somebody watches with a flashlight on the inside. A swipe along the seam (at the lower edge of the trim panel) with a dry tissue could help discover water intrusion.

Should it be leaking, the door panel is easily removed (easy for me to say) with a trim panel tool, carefully prying the clips around the perimeter and carefully unplugging the power window harness. An auto body glass shop should give you a length or sell you a length of 1/4" butyl sealant ribbon.

Carefully examine the plastic deflector for evidence of a void in the butyl sealant (at the bottom) and remove the faulty sealant, and clean that area with denatured alcohol and reseal that that section or just remove the deflector and redo the whole thing with new butyl.

If you don’t DIY then take it to a body shop. An auto glass installer may handle this for you at a reasonable cost. They do these all day long.

Let us know what you find.


CSA, Thanks a lot. This is new information. If this water leak problem in GM H body cars is known or common, will the new GM fixed it for free even I bought the car from the old GM? I wonder is it a design problem or quality issue? From your description: (…the butyl loosen up…), it sounds like a quality issue. Either way, do you think worth a try to ask GM?

Personally, I Wouldn’t Waste The Time To Ask. Every Car On The Road Has Know Idiosyncrasies (Some have really bad ones.), But You Can Ask. GM Has A Techcnical Service Bulletin (for their mechanics) On This.

Had this been a problem while the car was still under warranty, they would have fixed it. Car manufacturers have specific limits on warranties or they’d go out of business taking care of things like this forever.

Let’s not get the cart ahead of the horse, here. It would behoove you to see if you can “catch it in the act” the way I have described, above. Then go from there.

There are other ways for cars to leak. This just happens to be the first place I’d look. My Bonneville (same body) had this exact type leak. I fixed it myself in the driveway after diagnosing it with a hose, first.

You’re welcome and keep us posted. We all like to learn.


CSA’s right, no reason for GM to fix it. Part of owning an older car. Had this happened under warranty, they would.

OK, I understand what you guys are saying. Thanks again.