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Various Probelms Caused by Clogged Plenum Tray Drain on Audi A8 Quattro

Problem Description and Possible Solution

Clogged drains can allow rainwater to accumulate in the plenum tray (at the base of the windshield). The water may leak into the vehicle's interior, brake booster, or electrical components, which can lead to major problems. Our technicians recommend keeping the tray clear of leaves, pine needles, and other debris.

Problem Data
RepairPal Verified
Average mileage: 108,353 (55,000–177,000)
12 model years affected: 1997, 1998, 1999, 2000, more2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
31 people reported this problem
Viewing 1 - 13 of 13 comments
water running back into the car on both sides after it rains...how do i fix?
Plenum fills with water when it rains, leaks into AC vent work all the way into rear compartment. Also spills onto floor of front seats.
Water is leaking into the footwells,and a gurgling noise is coming from inside of the car .Sprinkles of water comes from a/c vents, when a/c is turned on. Also Battery light is coming on and the battery and alternator have been tested ,and they are both good.Moisture is believed to have gotten into the dash.The indicator,which lets you know how much gas is left,and when the car is put in drive,blinked out for about a month.All of a sudden ,it came back on,and that was when the battery light appeared.
Rainwater leaks in during heavy storms or Touchfree Carwashes. Water leaks in through HVAC System and comes through backseat AC vents IN WAVES.
I washed the car it ran. I turned the car off & locked it. When I tried to unlock it the security came on went off and radio, seats, etc. work but it will not crank. What should Ido I'm stranded.
Water draining on my foot.
ac condensation filled the front foot well.
I don.t know if its rain water or not but I have water leaking into the compartment and into the A/C/heating ducts also into the engine near the bottom of the windshield. What could possibly be causimg this problem?
Water leaks in through footwell vents front seat of car in floor
Rainwater leakin from the roof
I have this problem and at the moment am working to fix it. I managed to unblock one of the two drain outlets by putting a tube under the air intake box and pulsing it with compressed air. This sent a shock wave into the water which in turn blasted the water through one of the drain holes. I then put the car on ramps and got under the car so get a view of the plastic drain pipes. They are located directly behind the engine and with a torch you can identify them as a black tube which is about and inch in diameter but crimped in a cross at the ends to form a sort of valve. Unfortunately the crimped end means that just a few pine needles and other organic matter can sit in the tube, rot and eventually block the drain pipe. Once the water had drained I opened the crimped drain end and gradually dug out all the muck. It doesn't come out easily so persevere. As you clear the muck use a hosepipe and flush out by putting it under the air intake box until it runs clear. My instinct was to cut the crimped end off but haven't done this yet in case it serves to limit the amount of engine bay gases getting into the area of the air intake. Whilst I would not imagine this makes a lot of difference I am happy to leave as is and regularly clean the area.

DO NOT kid yourself into thinking you may not need to rip out the front interior, centre console, carpets etc as the water soaks through the carpet and fills up the soundproof foam. The water gets everywhere via the vent channels that run down the front of the foot-wells and down the centre console. All joints are push fit so the water escapes everywhere. In addition the access control module, phone module and on board supply control unit and diagnosis interface for data bus (gateway) central electronic control are all located under the carpet. Luckily for me I ripped out the interior pretty quickly, but even in a short space of time I was getting the following random faults:- 1. Key not recognised whilst driving. This is a real pain and can leave you stranded if you switch off the car. Go straight home if this occurs. I was lucky and managed to get home even after switching off, but it took plenty of tries to restart the car. 2. Alarm sounding, lights flashing and no response from key fobs. I managed to synchronise the keys again but with the water ingress this was a but random. To give you some perspective as to how much water can get in without you knowing, I removed about 7 litres with a water vac and even after getting it all dry, the next day there was more water which had drained out of the centre console soundproofing. Heaven knows how long it will take to get the water out of the carpet backing foam which is really thick and dense.

I would love to know what specific point of the air intake system allows water to get in and what sort of job it is to take the vent box under the bonnet out to check for damage as the main incoming flaps on the intake box do not open at all under any combination of vent control. If the job is not too difficult it would be good to remove it all so that the soundproofing can be dried out.

Everything is now out of the interior and I have reconnected the heater control panel and the key panel etc and restarted the car with full heat and AC on in order the dry the car out. I have let it run for several hours but I need a lot more time on this. I may have to get a high spec dehumidifier to do the job properly.

Personally I think the Audi vent system is a shit design and should be part of Audi's maintenance schedule as the consequences of a blocked drain means water will very soon fill the inside of the car and could render it scrap. Once I have finished sorting this out I will complain in writing to Audi as they have a responsibility to either make the drain clearing a task at every maintenance or advise customers to do this regularly, although I do not think the design and location of the drains makes this a user maintenance task. Having previously had a Mercedes CLK before this car I only wish I have never been tempted to buy the Audi A8. Yes its a lovely drive and comfortable etc. but the electronics are too fancy to be reliable. Heaven knows why they designed the electrical system such that the Multi-media system, cigarette sockets etc remain live when you lock the car. My battery usually requires an external charge if left standing for 2 or 3 weeks and the charging system does not seem to keep the voltage where it should be. Moans over. If anyone wants tips on the removal process you can find all you need on the internet but I am happy to respond to questions if I can help although responses may not be too quick whilst I am sorting this out. PS My location is actually Poole, England.
You can simply blow it out with compressed air, it drains under your car too
I just washed my car, tried to get all the leaf from the windshield and i got water in plenum tray which was full of leafs and all the water stayed in it, due to the plugged drain. According to my mechanic which is employed by Audi dealer for 15 years told me, to fix the problem will cost me lot of money! Luckally there is a site "car-parts.com" and i got used module for only 200$ and he was able to fix my car for 450$ total! From now on i will clean my plenum tray every month regular to avoid the problem!