[Qmulus]

Just saw this thread. I think the immobilizer under the seat is the "IMS bearing" of the 986/996 electrical system. A lot of Boxsters have been needlessly totalled as a result of this VERY stupid design to put a critical electronic device on the floor in a roadster. The first thing to do if you get water on the floor is to disconnect the immo or battery. The damage results from power being applied while the module is wet, as you get a kind of "electrolysis" which turns the metals on the board to metal salts, which will not stop until either the power is removed or the circuits open up.

As for the repairing it, it is good that you got it out and dried out ASAP. The problem is, if it gets to the point where functions start to fail, you have corrosion under the relays. The ONLY way to fix that is to desolder the relays, clean it up thoroughly (soap and water with a brush is good), dry it and repair the damage. That may include replacing relays. I would also replace the electrolytic cap any time the immobilizer gets wet.

I have a few immobilizers where the corrosion under the relay was not repaired and the traces under the relays got thin enough that they burned. That is a death sentence for the PCB as the board turns to carbon and conducts. While it is possible to repair the holes (BTDT all the time in a former life - cut out all burned areas, re-fiberglass, then put in new traces and vias.), I wouldn't bother, as you can almost always find used ones. FWIW, one of my first jobs out of school was working at an electronics company that did disaster recovery on main frame computers. I still remember getting a "mission critical" computer (DEC MicroVAX) that was in flood that was shipped in a big plastic crate full of water. It was better to leave it wet, and then disassemble it down to individual components. Even the disk drives were soaked, but we got all the data and rebuilt them another machine using most of the parts from their original. That job paid six figures as I recall, but the customer gladly paid. But I digress...

Yes, you can usually swap the EEPROM or EEPROM data from one module to another, as long as they are the the same part number. I do have a good memory map of where the various codes for the vehicle are (remote transponder codes, "learning" code, immobilizer code, etc.) I did find one immo where there was a firmware difference making the EEPROM data incompatible between two immos of the same part number. In that situation I had to rewrite the data in the proper format, so knowing where the necessary information to transfer was necessary. I find this situation is more likely when you go to a new immo.

So, for Fred I would recommend disassembling the immo, clean it with a brush and soap and water (it already got wet, right?), getting off ALL the visible corrosion (metal salts) as that stuff is conductive. You really need to get under the relays, as just spraying electrical cleaner, etc. will not get that corrosion out, and the only way to do that is to remove the relays.

As for my user name Qmulus, I have been using that on internet sites for 20 years and it is also the name of my company. I do this kind of work as a part of my business, but I honestly don't make much from it as this stuff take WAY more time to do than I can ever charge for. I see it more of as a "community service", but I can't do it for free.

Steve
Qmulus Technology