Same thing has just happened to our A6.
Blocked drain tube in the section below the windscreen. Water collects and comes in to the heater matrix and is then poured through the vent to the rear footwell vis the heater ducting. £2500 from Audi to fix and replaced damaged ECU etc!!!!!!

 

Hi Guys,

Well here is the latest update, and I hope someone might have some more pointers:

At the weekend I got under the bonnet to look at the battery drain hole. Please remember my car is right hand drive.

I took the seal off that holds the full width battery cover on and removed the full width battery cover. The first thing to note is that on the left hand side of the bulkhead (as you sit in the car) there is an exposed paper air filter type thing - I don't know if this should have a cover over it, but mine was exposed and the element felt damp although not actually 'wet'.

I undid the securing bolt holding the battery and tried to manouvre the battery out of the way. I don't want to disconnect the battery as I don't have the security code for the stereo. I could see a hole with a black surround (like a grommet) under the battery tray - the hole is approx 1" diameter. There were a couple of leaves and bits in there but not the usual crud you would expect to find. I wedged the battery up and cleared the leaves out. I then managed to get a small bit of rubber tube (only 4mm diameter as that's all I could find) to shove down the hole a few times.

The gulley under the battery did have a bit of water in it, but there was no standing water around this drain hole. I therefore wonder if either the water is coming in through the exposed filter or from the sunroof. The sunroof seal does seem to be good though, and there is no evidence of any dampness anywhere except the rear RHS floor.

The only other point to note is that the black weather / trim strip that sits at the bottom of the windscreen and goes under the wipers does not sit flush with the screen all the way across. It sits perfectly against the screen on the drivers side (rhs) and then there is a 3mm (ish) gap along the passenger side.

I hope that someone might be able to help as the car still stinks, and there is so much water coming through that it must be a big leak. If it was a door seal we would surely see it pouring in and that isn't happening.

Thanks again fellas, and sorry for the long post.

Stewart

 

Pics:

Here you can see where the trim doesn't sit flush with the screen:



Engine bay before trim removal:



Filter with what looks like a missing cover:

 

I had a pile of leaves under my battery. I disconnected the battery and cleaned it out. I have my radio code in my radio manual but the radio kept the code for about an hour. I lost the one-touch windows and the clock settings, no biggie.

The second picture is of the track that holds the cowl at the bottom of the windshield. It is spread too wide to clip the cowl properly. This is probably why you have water ingress through the cabin filter. There is a small gutter below this, but too much water will overwhelm the gutter.
I tried bending the track, but it would not move appreciably. I'm thinking of making a cover for the cabin filter to channel excess water to the side.

 

bump

 

Although the filter looks like is should have a cover, it does not. It should not be wet at all. The gap between the windshield and the plastic trim looks fine as well. Mine looks about the same. Just something to ensure no future leaks, see my photo with the air filter in it....now look at the a/c lines going through the firewall....zip tie that connector tight. That is NOT the cause of your water infiltration, but it can let a little water through.

http://picasaweb.google.com/lh/photo...eat=directlink
http://picasaweb.google.com/lh/photo...eat=directlink

 

The trim at the bottom of the windshield that is pulling away a little looks the same as my car but has me thinking. Water obviously is allowed to drain under it, and then there must be some sort of channel the water would follow. If your channel is plugged, it would overflow onto the air filter, down the hvac and onto the floor.

It's dark here in MN so I can't go outside and see if any of this is possible. But it's just a thought.

 

The trim at the bottom of the windshield that is pulling away a little looks the same as my car but has me thinking. Water obviously is allowed to drain under it, and then there must be some sort of channel the water would follow. If your channel is plugged, it would overflow onto the air filter, down the hvac and onto the floor.

It's dark here in MN so I can't go outside and see if any of this is possible. But it's just a thought.

 

Thanks for the reply Jeff,

I have looked at the car again today and have taped a plastic bag over the top of the filter temporarily. I have now mopped out the back floor of the car and as we have almost constant rain here at the moment I will check the floor constantly to see if it helps at all.

I have just noticed a pinch in the rear passenger door seal, but I have tried the trick of rubbing washing up liquid all around the door and window and then running the car with the heater on full and even after about 10mins there were no bubbles. I have also checked that the door drain holes are clear. I am beginning to worry that it might be a sunroof drain, but I can't understand a) how this would fill the rear floor with water but leave no other sign of water, and b) how the hell I would replace it...

 

Could be your HVAC drain:
http://forums.audiworld.com/showthread.php?p=14894864