987. Electrical fault lead to back half of car electrics going haywire when ignition off. How to fix?

There was heavy rain in London last night. The car was parked outside, locked with the ignition off. The immobiliser alarm was going off from 3am (though I didn't hear this but neighbours did). When I checked the car at 8am the back half electrics were haywire despite the ignition off. Here is a list of problems. 1) The hood control has tried to run and broken the actuator and bracket on the left side. See photo. Fortunately I was able to free up bits and manually at least get the cover panel closed. I'll deal with this later as a separate post. 2) The tail lights were on. 3) The immobiliser alarm was going sporadically. 4) The rear spoiler was up or going up and down with a life of its own. 5) The rear boot had opened itself. 6) There was a whiring noise from the rear of the car. I locked the car and disconnected the battery . To say I'm pretty upset would be an understatement! Let's leave the hood problem for another day/post. What is the circuit that is likely affected? Where is this, what is the part and how to do I get to it? Anyone else had a similar problem?

A classic case of a flooded rear control module. I think a bit of searching here will tell you exactly what you have to do - and unfortunately, it's not an inexpensive repair. Good first step on disconnecting the battery - but if you closed the frunk lid all the way, you'll want to search on writeups on how to open it when there is no battery . (Just saw your other post on trying to get to the battery .. I'll comment in that one..) I'm sorry to see this is only your second post. I can see where you're parked there are lots of leaves coming down, small leaves. I suspect you'll find one, or perhaps both of the water-wells in the rear recess for the top have plugged up drains. We have writeups on how to clean these and prevent future flooding, but the first step will be getting the car out of the rain and out from under falling leaves.

I'm wondering what the probability that taking the controller out, putting it in the oven at a low temperature of say 50C or in a bag of rice, and it actually starting working again. If the chances are more than half, it's probably worth trying. If not, then it's probably a replacement. FWIW after reading these posts I checked and their is moisture behind the seats. Seems like a rather strange move to have any sort of design where water can leak into the interior, and even more foolish to locate vital electronics at the lowest part of the cabin.

My rear electrics went crazy. Turns out (thanks to helpful posts on here) that this was the rear controller unit getting affected by moisture. My question is this. What is the probability that if I take this out, and slow dry it (say in a bed of rice at 50C), that it will come back to life? If the chances are more than half, I should give it a go. If the chances are near zero, I need to get a replacement and won't even bother trying to revive it. I know that when electronics are affected by water, sometimes the circuitry is fine but the water is shorting it, and sometimes the water actually corrupts and fuses out parts of the circuit. Anyone have experience with this?

Probability of success is about 0%. The actions by the controller indicate that corrosion has already occurred (electricity, dissimilar metals and water are never a good mix) and it's dead. Nailed to the perch. An ex-controller. Kaput. Try to find a controller from a car near the year of your car, but not 2009 or later, I think that one is different, and one equipped in a similar manner (one from a Cayman won't know about the top..) What I would suggest doing is removing as much carpeting as possible and drying out the area, disconnect the module from the harness so the connector on the harness can dry out (and hopefully isn't damaged).. while you search for a replacement. As far as why? Who knows why? Maybe an engineer who fanatically wanted to lower the center of gravity on the car?

It's worth trying, but don't hold your breath. I would drain it, then open it up to see how corroded it is. If it's heavily corroded, don't bother. If it's not, then you may have a chance to recover it. Take a picture of it when open and we can see how bad it is. There are a few threads here showing corroded RCMs... most of them did not survive.

Every convertible Porsche should have an asterisk “ garage suggested before purchase”.

A couple of comments . a. Instead of creating several threads regarding your predicament, it would be more concise and helpful for others to condense the discussion to one thread b. I'm guessing, based on the symptoms you've described, that the controller is already toast. It only takes a tiny short to fry a descrete device on the circuit board. You described things that indicate several controlled components have gone crazy. Drying the board is very unlikely to repair the damage.

.... Still, if you've got the time, why not give it a try? Water damage electronic recovery might be successful if there was not power applied before the failure. That doesn't seem to be the case here.

It’s free to rule out, why not? You know blind squirrels and finding nuts stuff.

The Rear Control Module is mentioned as the most likely cause. Is this the same, or related to the Immobilizer/CLU unit? I have come across a waterproof case for the aforementioned from Specialized ECU Repair. Reading through their website they mention similar symptoms when these units get water intrusion. If they are two different units, perhaps they make one for the Rear Control Module. One of those things you don’t think of until it’s too late. Like insurance, nobody wants it, but you kick yourself if you don’t have it.

Incidentally, the rear section being open like that is low enough that it shouldn't have flooded the interior, in theory. The rear flap there is not water-tight, so water would go past it and fall down into some specific drain passageways and then out the bottom. The water intrusion implies that you may have clogged drains as well, which is also something you should fix before it happens again.

Agreed - threads now merged.

Just an update. I diconnected the battery and closed the frunk. Stupid mistake. I had thought the one on the door sill was cabled. Interestingly the electrician fixed this by accessing the battery with a screwdriver between the windshield and bonnet. Clever. The red pin method didn't work. Next problem is the rear controler module is fried by water damage. Interestingly after a couple of days this seemed to come back to life and start working (mostly) again. The PCM warning was on and also it said to check the tail lights, but otherwise seemed OK. I took it out to have a look at this. As expected it was waterlogged and I opened the module and have soaked the board in surgical spirits. I will leave it for a few hours, then carefully air dry it. Looked pretty bad before. Lots of corrosion. Who knows, it is worth a try to fix it. Sensitive content, not recommended for those under 18 Show Content I'll post an update how I get on. If I can get this functional, I will be very careful with it going forward in terms of moisture. Then I need to have the hood lifters fixed. These were broken by the haywire rear controller unit. Currently three members on the passenger's side are broken.

I am disappointed that the board shows zero use of water/moisture protection. I thought it was standard practice to use a conformal coating at minimum.

Yes, and beyond that, locating it at the lowest part (where water will pool first) in the cabin of a convertible is daft too. I have an mechanical engineering background. If it were me, it would be a sealed container and wall mounted, likely behind a seat. Just crazy where it is. It's so little weight, there is practically no benefit having it where it is. It's such a wonderful car to drive but I am starting to fall out of love with it. The years 2000-2010 were not Porsches strongest time. I've only driven the car a few thousand miles and already had a broken coil (WTF - a broken coil in a Porsche for driving only on sealed roads), the nonsense with the frunk being unopenable when the battery is disconnected (esp given locking nut opener also under frunk), and now this problem with the controller badly placed/protected. It's just not reliable or well thought through. You don't have these problems with Toyotas (but they're not as much fun either).

German cars always seem, to have electronic modules mounted where water collects. Audis with the TCU under the floor just waiting for wet feet or a clogged sunroof drain. MBs with a battery and electronics under the seat where even condensation will build up a few inches. VW (Touareg) with the main harness (with splices) running down the side of the floor.

Odd considering the German climate. I guess it is what it is. As I understand it Porsche had brilliant vintages, and some pretty mediocre ones too. I'm told the post 2010ish Boxsters are a lot more reliable - not just because they are less old, but because Porsche generally ironed out the original problems over the years. Having said that, I prefer driving a big block normally aspirated over a small block turbo. But that's just me Given we're on a Porsche forum, I'm guessing many people have opinions on this.

Almost all cars get better with higher production numbers. I bet that Toyota builds, tests and crushes more of a single model than Porsche builds of a model like the 987 in a year.

Very interesting how your tech accessed the battery from the space between the windshield and bonnet. I had always feared the inevitable dead battery /frunk access nightmare, so came up with my own solution. You can explore it in the link below. https://www.planet-9.com/threads/dead-battery-frunk-access-problem-solved.256344/post-2233153

Very good. The thing with your way of accessing it is that you need to do this change it in advance, so you must already know about this problem in advance too. I didn't. Now I know about the problem, I'm happy enough with it as it is. No way will I do it again. However most people buy the car and have no idea about the draining ducts, or frunk/ battery chicken and the egg problem. It's almost like they need a big warning sticker on the dash for new owners - 'common gotchas'! Do you have any other Boxster gotchas people should know about? They are now my two ones now (frunk/batter and drains). My only one is that many of the older Boxsters use a bit of oil (not necessarily heaps but more than many other cars). Hence check your coolant, tyre pressure and esp oil regularly. Normal people don't think about this stuff. Mine takes about 500ml every couple of thousand miles. Yes - very impressed with the auto electrician! I must have read 15-20 posts on the internet about ways to get into a trunk when the battery is flat/disconnected. However this random guy who was sent to me from RAC had seen it many times before and had the fix. It was most unexpected.

Right, I did mine after reading of the problems others have faced with a dead battery . I wanted to avoid that in the future, unfortunately you experienced it the hard way. At least it turned out well. As far as the fabric top not sitting in the proper groove when closing, that is a common problem but is easily fixed cheaply. I did mine using some elastic strapping and a heavy duty clamp style staple gun. There are many methods others have employed, you can search this forum or YouTube for options. Below is a link to one of the many videos on this topic. You will be amazed how easy it is. At a recent visit to a local reseller, I noticed this problem on one of the cars in his inventory and when we spoke about it he said he typically pays $500 to send it out for repair. He was shocked when I showed him how easy and inexpensive It was to repair in-house. Good luck with it.

Ok - some good news. I cleaned up the circuit board by soaking it in rubbing alcohol with a little light bursh rubbing. Allow to room dry. I dried the area in the car thorughly and replaced the controller module back into the car and put the seat back in. Everything seemed to work normally except there as a PCM warning light on the dash. I took it for a quick drive up the road. While not ideal in London and just for test purposes, I gave it a little stick and got spin on the rear wheels (no PCM ) however after this the PCM warning went away and driving seemed to go back to normal. Bringing the car home, all seems normal now. Still leaves me feeling a bit icky in case the controller module is damaged and going to fail sporadically, but so far so good! For now I have to tentatively assume this is fixed. Thank you all for your help!

Just a quick update. For now I seem to have got the controller dried and functional. The remaining problem is fixing the hood lifting mechanism. There appears to be two or three connections broken on the left side, and possibly one on the right side. I'll probably buy the replacement parts and get my mechanic to fit these and service the car (it's been 2.5 years and 3000 miles). Anyone kind enough to point me in the direction of the parts for to replace the hood lifter mechanisms?

The failures were probably caused by "short circuits" caused by the corrosion being conductive. Since ot is likely to get wet again, I would take it out and spray the board with a confirmation coating.

Nice job cleaning up the board, windsurfingstew. It definitely was scary looking in the before pics. It was a gamble, but it paid off. Glad you were able to get things in order.

I'll add my congrats at your success in cleaning and reviving the circuit board. I suggest finding a shop that can run a full diagnostic check on all the systems. There might be some malfunctions you haven't noticed. Also, it might give peace-of-mind to buy a good Porsche specific OBD2 tool so you can run your own scans periodically.

That arm broke? I've never seen that before. Something really radical was going on when the module shorted out... What's going on here? It looks as if it's attacking the fabric of the top... The two rectangles point out the edge of the top fabric is not falling behind that window frame member. That might be because the part sticking out of the top opening was flailing around and broke the elastic that pulls that edge into place. Looking at the damage to the top - I might suggest that you look for a description of removing the entire top mechanism and top. It's not as hard to do as it might seem. I'd also suggest if you haven't done it already get a subscription to AllDataDIY for the car - that should make a number of things clearer. That's the sort of thing that would keep me up at night...

I'll just comment that everything you have asked about has been answered in posts on this forum. Forums aren't like Facebook - what we write sticks around and you can search for information rather than having repetitive requests for the same information. When that happens people will usually do the search for you and then post the link here. It would be nice if you at least gave a shot at searching here, or even just scrolling down the list of post topics in the DIY section of the forum. To do a detailed in-depth search of this forum, I suggest you ignore the built in search tool (it's marginally useful - but only marginally) and tell Google to search the site. The syntax for Google is in the Google search bar - "subject you need searched" site lanet-9.com- sorry about the smile - the editor does that, not me. Let's give it a run.... That resulted in 4 pages of hits on this website - and this website alone. And photos from some of the threads were included at the bottom of the pages. Take a look at the first item returned in that search: https://www.planet-9.com/threads/987-boxster-roof-elastics-replacement.253021/ HEY! That looks familiar. All that info need not be entered again. As I said - we're not Facebook with no memory and disappearing for no reason posts. Forums can be a really powerful tool once you know how to use them. And I'm repeating my suggestion you buy a subscription - even just a month - to AllDataDIY.com for your car. I subscribe by 3 year chunks - and get value from it every time I use it. Good luck. I believe your mechanic is going to have to remove the entire top mechanism - and perhaps that's best route to take to get it fixed in a reasonable time. And excellent job rescuing the electronics. I never would have guessed they could be rescued after seeing the amount of corrosion on them. Since you're now intimate with the boards, it might be worth looking for a non-conductive waterproof coating that could be used on the boards.. might prevent this sort of thing happening again.

Thanks Don. Yes, I think now that there so much is wrong with the roof lifters that the whole lot will need replacing. I had thought it might have just been one or two parts, like most other posts. Not to be. On the elastics, this was like this before (about 5% of the time going outside, ie occassional), so I was focused on the other parts. Apologies if I've given the impression that I didn't search first. I did but didn't find what I was looking for. I have a very basic working knowledge of mechanics but not for this car. Sometimes terminology can be different too as where I'm from we call the soft top roof a 'hood' and would never have expected the roof falling on the outside of the channel being 'elastics'. I thought it was important to put in as much detail as possible about my own situation. This forum has been very helpful in helping me get to the bottom of my problems. Like most things, it's turned out to be much harder to fix than I'd expected. Thank you!

As a onetime audio electronics hobbyist, I would have bet big money against a rescue of that circuit board—Bravo!!

On my first 987 Boxster , the rear wing would go up as normal, but it would stay up and not go down automatically. This would trigger a warning light for the rear wing. I replaced the entire wing mechanism to no avail. Then I pulled out the control unit from under the driver seat and saw some crusty stuff on the PCB. Cleaned off the board and it worked until someone broadsided me and totaled the car. So this fix did work for about a year and a half. How much longer would this fix have worked?, we will never know due to someone on their phone running a stop sign. I was surprised that the control unit under the seat was wrapped in a plastic bag when I removed it. Now I know why. This was someone's idea to protect the unit from water intrusion.

Don, thanks for the search tips. I have also been frustrated at times using the built-in search function of the forum, especially when the options are: SEARCH COMMUNITY, ENTIRE FORUM, or THIS THREAD. So your suggestion of Googling the query with the addition of ‘planet-9‘ seems to be a great back door way around it. And tork987, funny you came across the control unit wrapped in plastic. While following windsurfingstew’s travails of his waterlogged module, I wondered about the rather primitive, yet effective method of just wrapping it tightly in heavy mil plastic and securing the wiring harness with a zip-tie and maybe some sealing goop or hot glue where the wires exit the plastic bag. Cheap, easy insurance that can only do more good than harm.

I would worry about moisture getting into the plastic bag and staying there. It's almost impossible to seal up bundles of cables to be air-free, and if air can pass through them, then moisture can travel along with the air. One thing used many years ago on BMW motorcycle speedometers that were too well sealed was a Goretex membrane - keep water out while allow air to pass through was the theory. Dunno if the theory actually worked or not - but BMW later modified the instrument cluster with a 1/8" hole through the back of the case where the electrical connector was. For the great part - that solved the problem.