Sten

Especially if you live anywhere it rains - attached pic is of the PDAS/ABS control unit from an 89 C4 (not mine, I'm glad to say). The car had been left standing outside for ~18 months, and is now being re-commissioned. It appears that water has leaked in past the bonnet seal, run down the inner wing, and soaked through the cloth binding of the wiring loom heading down to the control unit - the inside of the connecting plug was full of water! Needless to say, the pins of the control unit have well and truly rotted away, along with a couple of the terminals of the plug. You can get the plug terminals from Porsche, part number is 903 353 03, but they're a real pain to replace. A new control unit from Porsche is £2340 + 17.5% VAT! I'm going to open up the control unit to see if I can desolder the pins and replace them, as I have a 'dead' unit on which the connector is OK. As a preventative measure, I'm going to re-bind the loom with PVC tape to stop it happening again.

DaveK

I think this is quite a common problem - Adrian has mentioned it several times.

Unfortunately, it's difficult to know what to do about it. I don't have any ABS / PDAS problems at the moment and I suspect that if water has got into mine, going anywhere near it and messing about with the connector might kill it off completely. Whenever I see it mentioned it does make me feel like I'm probably sitting on a time bomb.

Pesty

A real mess for sure. Barry I do not know where this unit is located is it possible to seal the plug from water or should we just sprey with water repelent WD40 ect etc from time to time.

My bonnet seal does not seam to leak but I do sometimes get condensation in there.

Adrian

This colour image is a graphic explanation of what can happen. Your right Dave it happened to me twice. I even used "Expensive Aircraft" methods of trying to keep it dry and the corrosion out and that failed after five years.
One thing that I was working on and sincerely recommend to any 964 C4 owner who has to leave their car outside in the rain is to try and work out a way of mounting the unit upside down. This will stop the water pooling in the connector. The big killer is of course winter and the salt, plus one must keep the luggage compartment seals in good order and ensure the drains work.
I did try and repair this myself, but the way the unit is assembled defeated me with my inadequate equipment here at home. A company I know very well which repairs DMEs would not even tackle this puppy and yes the new units are seriously expensive. I paid £190 for a second hand unit the first time around. The second time the control unit was over £2000 new and £1200 second hand. This was far too much and I sold the car. It was going to sell it anyway, but this reoccurence saw it go a little quicker and it was discounted for the problem.
Ciao,
Adrian.

PS: Do not use WD40 on these control units. WD40 is a lubricant not a cleaner and it doesn't evaporate. You cannot repell water in these units you have to dry them out. I saw somebody spray WD40 into a radio once. The result was not pretty. The problem with this system is that Porsche/Bosch in their infinite wisdom used dissimilar metals for the male and female pin connectors. The male pins are copper underneath the top coating and if they are scratched and the copper is exposed they are gone within a year under salty road winter driving conditions.

PWW

Thats an eye opener...time to go check mine.

Bangkokian

There's several different products used in the electronics/telecomunications industry we used when I was in that sector. Lots of different moisture repellent sprays for electronics and also dielectric greases (Dow Chemicals?) keep moisture away from the contact points.
These are often used on outdoor telecomunications connectors and work with relatively good success. Unfortunately I cannot remember the brand name of the products, but perhaps will run accross it considering I just flooded the inside of my car.

Adrian

Yes this true Peter, but I bet (in fact I know) that none of the cables and connectors used in outside electronic or electrical applications have a great long wick which sucks water along into the connector. The black material Porsche used to wrap these looms up with acts just like a wick in a Kerosene lamp except it sucks up water instead of fuel.
Added to that none of these outside units are positioned so that the connectors can actually fill up with water. Unfortunately there is nothing made on this earth that can keep water away from exposed metal contacts when the water flows over them from the top down and from the bottom up at the same time. Plus you have to remember that car connector pins are not made from the highest quality materials and often the control unit manufacturer gets quite angry with the car manufacturer on this subject.
Ciao,
Adrian.

Devils_son

Since my C4 is standing outside (I don't have a garage) seeing this thread kinda worried me. I checked it out and the pins still look like new, no moisture whatshowever. Must say that I replaced luggage compartment seals the moment I saw that they were not 100%.

Bangkokian

Adrian, you're most likely much more correct than I am. I read your book (own two) and know you're THE expert, so who am I to argue. ;-)
However I do recall that we went through much thralldom trying to find ways to keep water from entering the equipment/cables and keeping communications connections from corroding. For example any pin hole in a cable jacket, or crack/slot in a connector would result in water migration until it met some sort of water damming material. I'm sure that automotive cables/connectors will have the same properties. To accelerate problems, moisture in the vicinity of the electrical connections/transmission will quickly result in corrosion, especially because of the electrical conduction. This area was where the use of dielectric grease would really help out.
Hence, I venture to guess that some form of damming or prevention of water intrusion would result in at least some additional resistance from the corrosion process in automotive connectors/cables too. However what I also know from my past telecommunications experience, it's not easy to stop by any means.
Anyway, just my two bits worth.
By the way, you write great books!

Adrian

Peter,
As I said the real killers are water mixing with the salt from the roads in winter.
My personal solution for this issue is to turn the control unit upside down. This will ensure the water cannot migrate down into the carside connector and water cannot pool in the unit connector from running down the outside of the car connector.
Owners may have to manufacture some form of plate to mount onto the existing mounts and install the control unit upside down onto studs installed in the plate.
Short term I would consider undoing the unit and putting it on the top of the lower secition of carpet on its side. I know the unit runs like this because I did some tests a few years ago with it loose in the luggage compartment. Stick it in a plastic bag and tape it down to the carpet. Ensure a corner of the bag is cut off to allow ventilation.
Owners who are concerned need to keep an eye on the luggage compartment carpet. If it's wet or frozen during winter, water is getting in or there is large build up of condensation inside the luggage compartment. Filling the fuel tank with warm fuel in cold conditions creates a huge amount of condensation in the 964. This is why drains must be checked.
Weatherproof car covers are also a must if you can find one that really is weatherproof. They are available, expensive, but cheaper than a control unit.
Again before people start to panic this problem is pretty well isolated to 964 C4s which drive on salted snow/roads in winter and spent their parked lives entirely outside, 964s which live unprotected in tropical environments and flood damaged cars that were left outside and not immediately dried out.
Ciao,
Adrian.