Eddie123

Hello.

I have found that there is leaking water into my 2001 A6 C5, on the driver side. This only happens when it rains heavily.

I have investigated the forums a bit, and have found that this seems to be a common problem, but the instructions on how to fix it, or what is causing it , is a bit unclear to me.

Can someone explain how the drainage system works on this car ?

I have looked in th eengine bay , underneath the windscreen. I can see that the water collecting box under the battery seems to be dry, but I have spotted water underneath the E-box. How is the water draining away from underneath the E-box ? Does it have its own drain hole, or does it flow into the collection chamber underneath the battery ?

Thank you for any replies.

CRuby

There are 2 drain holes in the compartment that houses the battery, brake reservoir, etc. One is directly below the battery tray, & the other is near below the heater hoses.
Both these drain holes should be checked/cleaned periodically, because if clogged, they could lead to water pooling in that cavity.

Eddie123

Thank you for your reply and pictures ! Much appreciated.

As far as I can tell, there is no water under the battery, so I presume the drain work there. I can of course test this with some water, pouring it in there.

But i can see water undeneath the E-box. And as far as I can tell, the bodywork under the E-box i situated higher than the drain holes, which must mean that the water under the E-box is meant to flow down into the battery well.

Can anyone confirm this ? I could see a lot of sand / leaves etc on the side of the E-box, I have tried to pressure blast there, but it is a very tigth spot. That is why I also ask if removing the E-box is an easy job ?

CRuby

I expect you mean outside the ECU box & not inside it, right?
ECU box is in the same cavity, & drains to the same 2 drains. As you said, ECU sits up a bit higher, but water should flow toward the drain below the heater hoses. If you see water outside/below ECU box, it's possible that you have stuff clogging the path to the drain holes. IIRC, I had rigged a hose to my shop-vac to snake it around below the brake booster & brake reservoir to clean that area. I've removed the ECU cover & ECU before, but never the bottom box portion itself. I expect it has a seal between it & the car interior. I recommend not pulling the box yet, but vacuuming up most of the "sand/leaves" surrounding it, and especially below the booster & reservoir. Also, check to make sure both drains are clear.
While you're at it, you could open the top cover to the ECU box to verify no water inside the ECU. Obviously, you don't what any water inside that box.

Here's video showing an extreme case of clogging.

Eddie123

Hello.

Yes, I mean on the outside (underneath). I can see there is standing water under the ECU box, so my guess is that there should be a channel for the water to flow that is clogged.

I dont have a powerful shop vac, but I will try to blow underneath with compressed air, maybe that will clear the path for the water.

Jerry L

Get your hand down in there behind master cylinder after you vacuum there is a rubber lip like seal that pops into a hole in the bottom of that compartment sheet metal others plugged up, it is a right fit but once you either vacuum and see or reach in and feel it you will easily fix this you can even pull the lip seal and clean / wash it the lips inside it are ment to drain water, works till it gets dirty & clogged

Regards