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Discussion Starter · #1 ·
As described in other threads, my '08 451 was having problems with the transmission that were at least partly caused by water and resulting corrosion in the Transmission Control Unit (TCU). What I am now trying to figure out is where the water came from and what I can do to stop it from getting in again.

Under the carpet is a closed foam of varying thickness. Up to around the middle of under the seats, the foam in my car was saturated with water. The TCU is not sealed, so water got into it. The water also corroded the wiring harness grounding point that is also one of the bolts that holds down the TCU.

There was no water at the TCU when I was looking at it to diagnose the transmission problems, but the corrosion was a clear sign that it had been wet at some point. It was just ahead of the TCU where it was saturated.

Where could the water be getting in from? I imagine some of it was from melted snow tracked into the car, but the car hasn't been driven in the snow for a couple years.
 

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If it's a Cabrio, roof might not be seaed
If memory serves me correctly, around the battery there's an ac drain hose, per maybe just a plug that lets water drain. Anyway, it might be clogged with dirt
 

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Discussion Starter · #3 ·
It is not a Cabrio.

The forward portion of the carpet is damp on both sides. The AC drain hose should be on the outside of the passenger compartment, right?
 

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Cars and trucks have an a/c drain hose because as we all know “ the a/c system sweats”, anyway this drain hose gets clogged up with leaves and whatever, when this happens water builds up in the evaporator housing and eventually will overflow the cabin area.
 

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Discussion Starter · #8 ·
Got it.

Routing that line into the passenger compartment is unusual compared to the other cars where I have worked on the A/C. One of my specialities is removing A/C systems such that it looks like the car was never optioned with A/C. The box that the evaporator sits in has always had a portion hanging outside the passenger compartment and the drain line would attach there.
 

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Got it.

Routing that line into the passenger compartment is unusual compared to the other cars where I have worked on the A/C. One of my specialities is removing A/C systems such that it looks like the car was never optioned with A/C. The box that the evaporator sits in has always had a portion hanging outside the passenger compartment and the drain line would attach there.
Welcome to the "quirky" world of the smart car... :D
 

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Discussion Starter · #10 ·
Where does the drain tube clog? Does it separate at the elbow where it goes through the floor at the battery?
 

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Where does the drain tube clog? Does it separate at the elbow where it goes through the floor at the battery?
It clogs at the exit of the tube, under the car. You have to remove the under tray to find the exit of the tube. It's very narrow, and the factory fix is to shorten it a bit (at dotted line) so the exit is wider. :)

65136
 

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I also have an 08 Passion and I experienced water saturating the passenger compartment floor area. I exposed the battery area and found the battery compartment was full of water. I determined the water was coming from the AC drain line. The line was clogged where it flows through the battery compartment and I unclogged it by blowing high pressure air through the drain in the battery compartment. I also pushed a piece of wire through it and the water drained with no more problems.
 

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Discussion Starter · #14 ·
It clogs at the exit of the tube, under the car. You have to remove the under tray to find the exit of the tube. It's very narrow, and the factory fix is to shorten it a bit (at dotted line) so the exit is wider. :)
Aha! OK. Mk4 Golfs have a similar design for the sunroof drains with a similar fix.

Today I lowered the front of the front undertray to look at this and the brake pedal switch. The car now won’t shift out of park after I start it until I clear code C1034 with the MB II. However, I was working outside and it started to rain, so I closed things back up before I could get a close look at either the AC drain or the brake pedal switch. No rain in the forecast for tomorrow, so I’ll try again then.

Does the front undertray unclip so it can be removed?
 
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