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2005 955 S w/~127K I recently replaced my coil packs (my first time this deep in to this car) which ended up being a great idea as it solved a very odd electrical problem (different thread) but whoever replaced the plugs last used a pneumatic driver or something to screw the bolts in to the head that hold down the coil packs. One of the studs was cross threaded, two more somewhat cross-threaded, and one of the studs was broken off flush with the head. Idiot! It wasn't me... i swear. Funny thing is I have been riding around with it like this for a year or so... with nothing but friction holding the coil pack down.. But it really bugs me for it to be that way so I decided to try to remove the broken stud after a few drinks and one youtube video that made it look easy and a chearp harbor freight extractor. It actually was going quite well until i broke off the extractor in the hole, and then a drill bit trying to remove the extractor, and then everything went to hell two more drinks later and I really farted up the whole thing beyond repair... Idiot! What to do? Can this brass insert be removed without removing the head? should i have a machine shop or something drill out the bolt in to the brass area (margins) and re-thread it? can i have someone just weld a small aluminum anchor on either side of the coil pack to put some wire over the top of the coil pack to keep it down? high temp jb weld for instead of welding? glue the coil pack to the head? just leave it as-is? Don't really care what i looks like... just don't want to have it come loose on me.
Success!!!!!!!!! ? !!!! After replacing the coil packs I have been unable to recreate this problem! I've been able to recreate the problem 90% of the time and have experienced it probably 200 times but it happened almost 100% of the time in Summer. I've driven the car 8 times after replacing the coil packs and have not been able to get the charge/alt warning light to re-appear, even when putting the hot car in gear immediately after starting... the method i could get it to stick at 12v for a LONG time... (up to 40 minutes) and no A/C during that time. I've tried to make it fail the last couple days and stick at 12V and I can't... something about changing the coil packs appears to have fixed the problem. 4 of the remaining 7 coil packs were older/non-branded... 3 of the older ones were newer Beru but i replaced them anyway and kept the old Berus as spares. I'll keep testing and report back again... I can't explain why... I may try to test the coil packs... ohms? not sure how...
My local Porsche mechanic has a Durametic and pay$ monthly to Porsche for it. I'm scheduled to have him do some coding for the factory tow module (ebay) I installed that appears to be set for Europe (separate, but not uncommon problem) and I'll ask him about it. I brought up this problem before to him but it stumped him and he is assuming it is a alternator replacement job (although he didn't like/think that sounded right). I haven't given up on this.. just have bigger fish to fry to prep for a big trip towing a new camper later this month across the country. This problem isn't new, I have a semi-reliable work-around, I don't think it will leave me stranded, etc. I'm also about to install new coil packs (I had one fail on me recently) , should have ordered all eight, only ordered one, and now I think it best to go ahead and finish the job before the trip. I'm also hoping, wildly, that maybe the coil packs have something to do with it. The coil pack that failed was a cheapo non-Porsche, non-Beru knock-off. It broke apart in the cavity and took 4 days of digging around with home-made tools and stats to remove the broken pieces. Hopefully the others come out easier... if not they can't be as hard to access as that one (#4). I've read others say that faulty coil packs can do odd things once they heat up... which is a coincidence that this problem only occurs only after the engine is hot... ...? In either case they should be replaced... then I'll tackle the stupid voltage problem... assuming my trailer wiring doesn't present a problem I have to work on more. Before you ask, the 12v problem existed before the coil pack or trailer stuff was installed. I also considered pulling ALL fuses for ALL things not absolutely required to see if that made a difference.. or maybe borrowing a battery just to eliminate that.. Its a very easy to repeat problem that is 95% consistent....
I had a leaking radiator overflow reservoir to replace this weekend. Job went fine until the very last step, clamping down the headlight. Ended up breaking the headlight bracket ;< To the point: I spent another hour or so locating the module which is exactly where you thought it was. The bracket that holds it uses clips and one bolt to hold it to the frame. Of course the bolt is in the one corner I can't get to without removing the lower dash. I spent most of the time trying to remove the plastic lug that holds the ignition.. Everyone says it just takes a flathead uses the notches. Much time and lots of slips/scratches later I just couldn't remove it. I suppose I need to buy the special tool or a replacement part and just break it. I was able to get the part number off the module so my plan is to locate the tool, replacement plastic nut, and module and try again. Meanwhile the problem persists... never happens in the morning until it runs awhile... doesn't even have to be THAT long... 5-10 minutes... next start 12v... I'm thinking more and more it's not the module but I'm willing to go ahead and try it since I haven't heard any other logical explanation.
PigNib changed their profile photo
There! Notice your diagram's part 15 is the same as where my diagram's parts 11 & 12 (relay terminals) fit. The website shows all the relays in 11 and 13.... relays in 13 are mostly show in the screncap... servotronic, rear lid lock, air suspension relay, fuel filler flap, etc. You would think you could find a document showing the location of those but I've watched tons of videos and watched lots of websites with diagrams that seem to show all fuse boxes and relays EXCEPT for those..
Still trying to figure out how to do in-line photos
Getting closer! Using the website you used (good resource!) I found another diagram that shows the same carrier part for the control unit attached to these relays. Unfortunately with all my searching and knowing what relays are next to the control unit i STILL can't find out where it is yet. I guess these relays don't need to be replaced often. I'll keep looking... as soon as i know i can get to the control unit I'll buy a replacement and try it. SURELY if there are relays near by it can't be THAT hard to access. Thanks for helping even though you don't even have a Cayenne anymore! 2019-09-19_07-38-14.snagproj
Wow this is the first I’ve seen that suggested. I’ve read a half dozen or so people on various boards having what appears to be the same problem. Several times the battery and alternator were not the root cause. A couple just cut the exciter wire to force it to always charge. This part is $550 new but can be had for $30-50 on eBay. That tells me not many people replace the part or need one which IMO reinforces the theory that may be it. I usually think of cold being a problem with circuits (solder joints) but heat could do that too or maybe skew a discrete part like a resistor or capacitor out of spec. It’s a long shot but I’d be willing to buy one and try. Where the heck is this thing? Hella-hard place I’m sure ;) I’d much rather take apart a dash than work the same amount of time in the engine compartment. I also would like to test the exciter wire voltage. Anyone know if it’s accessible without removing anything difficult? I’m planning on hauling a camper with Electeic brakes end of October and would love to figure this out before then. Also if anyone knows of what to look for in the Porsche tool my Porsche shop (not dealership) is always willing to do that kind of thing for free if I do the research and tell them what to look for. Thanks for the reply! (Off to search for my own answers) Sent from my iPhone using Tapatalk
Sending this duplicate response from similar one on rennlist: Joining this thread not to hijack it but hope to help. I have these exact problems/symptoms. I wish i remembered exactly when it started and what was done before/after. I’ve had this problem for over a year. It seemed to first surface last summer ( we get hot ones in Arkansas ). I had a starter problem ?before? This happened and had that replaced after replacing the battery first (it was old and was hoping that was all it was. I’ve also had headlight problems ( I have xeon) flickering and going out because of the known problem of wire coatings disintegrating in the bulb housings. I’ve fixed that with liquid tape (I think) and do not think it is related. The below statements are repeatable and almost always consistent. The first start of the day the volts (dash gauge) always jump to 14 quickly and the A/C and fan kick on fine. Once the bolts hit 14, regardless of the condition, they Have NEVER dropped back to 12 while driving or while the engine remains running. If making a quick trip in somewhere I sometimes just let it idle so I don’t have to restart it and wait for the volts to go back to 14. After driving for a while and the Engine gets hot the next time I start it (within an hour or two) the volts sit at 12 then eventually (usually within 90 secs) go back to 14 and the AC and fan kicks on. Until the dash reads 14 the A/C fan won’t blow. Revving the engine, shutting off electrical things, etc. do not seem to make a difference. When starting it hot hot and volts read 12 and I put the car in gear and drive the volts do not go back to 14 nearly as fast. During this time no AC fan and I have to roll down the windows in the 100 degree heat. The voltage almost always go back to 14. Sometimes quickly (2-3 minutes) but I’ve driven for 30 before without it returning to 14. Once that happens (driving without letting volts get to 14 first) stopping the engine, removing the key, then re-starting doesn’t seem to get the volts back to 14 within the 90 seconds like it normally does with a hot engine. I only do this if I absent minded lay forget to let volts climb befoee putting it in gear. Haven’t started diagnosing yet but I think this would be a LOT easier to figure out if we knew the computer if then else flowchart for how the computer (sends) voltage to the exciter wire. I don’t see anything in the diagram inline for the exciter wire. I expect if I cut my exciter wire ( forcing the alternator to think it was under voltage) it would engage and I would always get 14 volts. If true it really comes down to what is happening while the voltage is at 12v and the car is running that prevents the exciter wire from reducing voltage below what it needs to engage? Maybe I still don’t understand how the charging circuit works. I hear that all the electrical stuff really pulls from the battery, not the alternator directly. And the alternator isn’t always charging the batter, only when it drops below X volts. I assume this is to keep from overcharging the batter or just sparing the life of the alternator? if that’s true what condition would keep the ac fan from working ( computer shuts down because of reading low battery voltage ) but at the same time sending enough voltage to the exciter wire to keep the alternator from engaging? Those two things seems opposing. What damage would be done by just removing the exciter wire? Ill Try to gather more evidence. My porsche mechanic ( no dealers but he only does Porsche and lots of cayennes) says he has NEVER had to replace an alternator. Thanks! Jeff in Arkansas Sent from my iPhone using Tapatalk