f29pc

Just got a 2004 A6 quatro and sure enough after the first hard rain, wet pass floor. I went to clean out the battery tray drains and found the one under the brake cyl was plugged, the one under the battery was already removed (no rubber drain, just a big hole).
I pulled up the carpet, the TCU was dry as a bone (lucky), and dried out the foam and carpet. I still have the leak and narrowed it down to this.
With the battery out and the tray removed, I put a funnel in the battery tray drain hole, pouring water into the funnel with no water getting in the battery tray, the water is leaking in just below the evaporator drain. I opened everything up but cant see were it is coming through the firewall. The evaporator drain looks dry all the way around, but it is very difficult to see. Is there any way to access the area below the battery tray drains?
ANY suggestions or ideas would be a big help, this is driving me crazy!
Thanks

pineapplecharm

Did you ever figure this out? I have a strong feeling this is what my problem is - i.e. not the evaporator drain but something getting in through the firewall.

f29pc

I think I did! I didn't actually "see" an problem with the seam in the firewall but I did notice that the gasket under the cabin air box was really bad (not the one inside the box), and replaced it with a good bead of silicon around it too. I also replaced the plastic water deflector that runs along the bottom of the windshield (mine was cracked) and haven't had a leak since.

pineapplecharm

Curses. I know exactly what you mean about that crap seal around the pollen filter box. I drowned the thing in outdoor-grade sealant and thought I had it licked but six weeks later there was - no exaggeration - a gallon of water back there.

Evaporator drain seems to be draining fine (can see it dripping under the car). A plastic sheet under the rear footwell aircon outlet reveals not a drop after two weeks of alternately wet and hot weather (the only good thing about this summer is I'm testing both quite rigorously!). No sunroof fitted so it's not that either. The plastic seal under the windscreen came off to access the pollen filter box bolt and looked fine; I may put some of the sealant under it as per your suggestion.

The only concrete lead I have is the attached; I painted the front passenger footwell with food colouring and, after a week or so, spotted two little rivers in it coming down from under the dash. The soundproofing material felt damp too, although this hasn't happened again as far as I can tell. Is the evaporator up inside there? Could that be leaking that much water so quickly, even when enough is getting down to be visible dripping under the car? Seems like a stretch.

I can't tell you how tired I am of taking up the *&*^*&ing carpet and drying it out! Glad you got it sorted but if any inspiration hits as to what to check I'd be grateful for suggestions.

And apologies to all for the giga-bump but, like so many before me, I'm at my wits' end.

chedar

I'm having the same kind of problem with my 03 A4 1.8L.T, water leaking into the passenger floorboard behind the glove box, i've cleaned both drain holes under the battery, i've unclogged or cleaned the A/C line that goes from the passenger floor to the outside bottom of the car but I haven't been able to get something that is stiff enough to push through the hose but yet can still bend enough to go all the way through the hose till it ends up whereverit ends up at, I don't even know where the hole from the hose goes up at, Does it go into the engine bay? ''I'm assuming it goes to the engine bay''.
and my (FCM) fan control module or radiator fan control module doesn't work and I won't receive my new oem FCM til tuesday. And could a bad FCM have anything to with water leaking into the passenger floorboard?
sorry I'm ADHD so my questions and answers can get a little off track.

findalex

I think I've read people use the nylon wire used in the weed wacker. Something like this: https://www.harborfreight.com/10-ft-...-pk-56545.html

FCM shouldn't have anything to do with water getting inside the car.

tjf

I just helped a friend work on his girlfriend's Q5. Same issue with water getting in passenger foot well. At 1st I thought it was clogged drains in the plenum area, as it was filled with crud. It ended up being the seal for the water diverter, for the cabin air fan inlet. It can be a fairly common issue. A bead of silicone, windshield sealant, or even a strip of duct tape can solve it. It has few and far between retaining nuts, that don't hold it up against the firewall very well.

Keheuer

I just had this problem in my 2004 allroad. It seems like it's that pollen seal (kind of foam), it gets wet but it's not because of what you think. The bezel (that plastic apron at the bottom of the windshield) is not seated into the groove properly at the base of the windshield, letting the water leak underneath it. It pours onto the cabin air filter and then leaks down inside the air handler which makes that pollen seal down below the cabin air filter wet. You have to actually physically tap the bezel with your fist or with a rubber mallet, preferably, until it is completely seated into the groove at the base of the windshield. It was literally a 30 second fix.