Howdy, fellow BMW owners.
I have a mysterious problem with a wet floor (rear passenger floor, driver’s side). The sunroof doesn’t leak and spraying the door with a hose nor heavy rain doesn’t cause the wet carpet.
I’ve done a bit of research and it seems there may be a problem with the moisture barrier located between the outer and interior door. Does this diagnosis seem right?
Damn, these cars have some weird problems!
2002 (E39) 530i
Does it only get wet when it rains? Does the AC have to be running to replicate the problem?
Rain nor hosing down does not cause the wet floor, neither does the AC (I’ve tested it out a few times).
Never saw the word spelled before, would have guessed it as Beamer.
This is what I’ve been told: “Bimmer” is used for cars and “Beemer” applies to the motorcyles 
Odd. If it’s not rain and it’s not condensate, I have no idea what it is.
Do you have a cat? 
You got me stumped, but your car is too new for me, and I don’t know the 5 series.
I’m not really a bimmer person, but hey, a car’s a car!
If rain/hosing it doesn’t cause the damp carpet, then (assuming it’s not spontaneously appearing from nowhere - have you noticed any unusual cloud formations around the back seats? 
) water is getting trapped somewhere, and leaking in over time.
Likely culprits:
Door filling with water and leaking in through the side - if you swing the door around, can you hear any water sloshing? Check the drain holes at the bottom of the door aren’t clogged - I had that with a car once and when I cleared the blockages about two pints of water poured out the holes.
Roof guttering - are the seals along the roof/tops of the doors intact? Are any areas damp when they shouldn’t be?
sunroof - you say it’s not leaking, but most sunroof designs have some sort of drainage system - usually rubber hoses going from the sunroof down the B/C pillars and out to the ground. If they’re blocked or perished, then water could be leaking in that way.
If not that, could it be coolant? Are you losing any? Does the carpet smell sweet? I can’t think why you’d have coolant hoses around the middle of the cabin area, but you never know.
You might also try one of the BMW forums around the web. The guys at bimmerfest in particular have been very helpful to me with my car.
Is there any specific odor? That might help.
There is also Bimmerforums. I have found them to be… slightly less helpful. Standard reply is usually, “Buy a new one”. :rolleyes: Might check it out however.
check your trunk. see if the trunk mat/spare tire well is wet. Not a BMW, but my last car (an SRT-4) had a water leak through one of the taillights, it eventually collected enough in the spare tire well to slosh/seep forward and soak the rear carpet. after re-sealing the taillamps, I had to pull the entire interior out and leave it out in the sun all day to dry out.
Pop off the interior door sill trim, pull back the carpet, grab a flashlight, and get inside. Have someone spray the car while you watch for any water trickling down from the door jamb area. Also look for streaks where water has previously been coming in.
Park the car on level ground. Open the sunroof. Get a large glass of water. Carefully and slowly pour the water just inside the sunroof opening at the front and back on each side. Look for each corner to drain onto the ground. The fronts drain on each side usually near the firewall. The rears somewhere near the rear tires. If any corner drains slower than the others you have a plugged or kinked drain hose.
If everything is Ok there have you visually inspected the AC drain?
Finally look in the trunk.
Do you live in the upper Midwest by any chance? Back in the bad olde days, the carpet would start getting wet back there because the floor pans were rusting out and the carpet was the only thing between your passenger’s feet and the slush. Most newer cars don’t rust like that anymore, but with an '02 BMW I might maybe crawl under there with a flashlight and have a looksey.
Yeah, where do you live, what is your weather like and how often does it get “all worked up”? Might help to determine if moisture is coming in or going out (hard to imagine a scenario where its going out on a regular basis).
On the old e30’s, the fuel pump is located right under the rear seat driver side, but I’ve never heard of fuel getting into the cabin, and surely you would know if it is fuel. So we’ll rule that right out.
I’m guessing sunroof if it rains any where you are. Those door panels are pretty well sealed from the few I’ve seen in the junkyards. (Hence, my unrepaired rear power window)
This came a bit later but BMW had some problems with door seals the mid-2000s. The adhesive gave out and leaks resulted.
Does it only happen in the rain? If it only happens in the rain, it’s probably a leak. If it happens when it’s not raining as well, it’s probably the AC leaking back into car.
Actually, it never happens when it rains. I think a blocked AC is the first place to start.
I’d bet it would if you cranked up the AC. Assuming there isn’t something else going on like ‘it doesn’t happen when I drive in the rain, but it happens about 20 minutes later’ but if it happens even when it hasn’t been raining anytime recently, the AC is the first place to start. How comfortable are you with poking around? If not, next time you get the oil changed have them (assuming you don’t go to a quick lube place) take a look at it. Normally the drain gets clogged up and needs to be cleaned out.
I need closure!