A Cautionary Tale

For all those cabriolet owners whose cars are perhaps three years plus I strongly recommend that you check the roof drain outlets which are located behind the rear plastic wheel arch linings. For if these get slightly blocked then, when you wash your car or are in any sort of heavy rain, there is a strong probability that the small internal resevoir will overflow. The resevoir is located behind the rear side panel and is ideally positioned so that the water overflows down into the rear seat and the rear floor well. This area is linked to the front floor well via the well below the front seat and trust me it is no coincidence that these areas are called wells for they can hold a lot of water! Over a period of time you will be blissfully unaware that this is happening until it is too late. Then one day, whilst its raining, your car alarm will go crazy, your car will not start and it will have to be dragged of to the repairer. They will eventually find the that EC unit, which does what it says on the tin, has blown up. Why? beacuse its located in the well under the pasenger seat and as we know water and electrics do not mix. The cost of the whole operation was horrendous but the repairer didn't know how the water had got in. It took me the best part of a day to strip out the rear panel and find the problem and fifteen minutes to cure it, which is the time it takes to remove the rear wheel and lining and replace them. So when you have your annual service get them to carry out this little job - it will be cheap in the long run. PS. Boxsters have the same problem I understand. Happy Motoring.

Thanks, howie. Appreciated. Is this a DIY job or is there more to it?

Howie, A good heads-up there. This problem is apparently fairly common. You have been very unlucky however. Usually it just means a damp rear carpet, or intermittent starting problems. I was informed that a good precautionary measure would be to put the entire ECU in a plastic bag, so if this blockage does suddenly occur (between inspections) you won't have to face replacing it. Many times though, unblocking the drainage holes and blowdrying the rear passenger-side carpet will do the trick.

Wouldn't that set up condensation problems?

Is this covered under the ext. warrenty ?

Why?

Stuff in plastic bags seems to attract condensation unless the stuff and the air around it is absolutely dry when it goes in. Perhaps some of those little crystals you get in electronics packaging would help.

Thanks for that Howie. I am going to check mine this weekend. Sorry to hear you had such bad luck though. However, I am not sure I understand where this internal overflow resvoir is in the rear arches. Can you be more specific. May be some DIY instructions for us DIY numb skulls. Cheers

Silica Gel. But not sure where you would buy it. Does anyone know a reason why the ECU would ever need to be opened for repair or adjustment? I can only think that it would have to be replaced if went faulty. Given this, I think the best answer is to place the ECU in a plastic housing and fill it with electronic component potting epoxy. It may sound drastic but it would be air, water and vibration tight. It's usd a lot in avionic electronics especially in wing based equipment. But if the ECU has to be opened for service in the future then its no use as once epoxy potted, it can never be opened.

As long as the heat from the Epoxy curing does not damage some of the non-military-spec components, that would probably work (don't think of changing ECU mappings though [ ]) A bit drastic and risky mind - wouldn't checking for blocked drains be easier and safer in the long run? (And I'm puzzled as to where a reservoir would form as well - not saying it doesn't - just puzzled)

Potting the ECU might also prevent it cooling in use, which might prompt problems in the future. I wouldn't recommend that unless you know what you're doing.

I agree Mark, potting is a bit drastic. Just an idea though. As for overheating: As it happens potting helps heat coefiiciency to remain static in components. In fact some installations use it to simply to prevent overheating.

Fair enough! [ ] --------------------------------------------- Rule 1; when faced with someone who knows more .... shut up .....

The OPC would need to attach their diagnostic equipment the the ECU when servicing it, so the port would have to be made accessible. Also if there were any faults with the car, they would also need to connect it to the ECU to retrieve any error reports that would arise. I think the same box also contains other importnat chips such as the Alarm control unit etc

Hi, hopefully this will clear up any confusion. When the rainwater runs off the roof it drains internally and is diverted into an open plastic drain channel, from which it runs down into what is probably best decribed as a hopper - as opposed to a resevoir. From the bottom of the hopper there is a 10/12mm dia outlet which extends, via a tube - I think - down to another plastic outlet set into the internal rear wheel arch. This area of the wheel arch is covered by the plastic internal arch liner. Trust that clarifies things.

This really is a simple DIY job - the hardest part is getting the large rear wheels back on! There are just three washered nuts holding the plastic liner in place but it will not come out without removing the wheel.

Thanks Howie[ ]

Thanks for your comments, however, any water that overflows from the hopper - this better describes the item rather than resevoir - doesn't run onto the surface of the carpet, but behind it where it then soaks into the 50mm thick dense foam backing to the carpet. Even with a good 10mm of water in the foot wells you won't feel the carpet damp.

Well I never had time to check this yet but I certainly will do at the weekend. Many thanks for the heads up Howie...

Kim on renntech had previously posted details about this problem. FYI, here is his posting. It doesn't say anything more than Howie but it may be useful :