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2000 Porsche 996 - Battery Drains - The alarm Horn is a constant 3v an

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Hi all


Hope everyone is well!


I'll register now for the Rentech Continutor - thank you.


Ahsai - i'm not sure what that green connector is, i'll take a look at the engine later and see if I can identify what it goes to. It should be something original as nothing looks out of place on the car at all.



Alternator -- so the alternator was at fault, I just spoke to the place where it came from and they confirmed that a diode-rectifier fault can cause a quiet hum. So I'm hoping to remove it this sunday night , send it back Monday (there 300 miles from me) and they will repair it for later in the week.    As my 1955 VW Beetle finally went to the USA yesterday...,  I now have space in the garage so will be able to park the car undercover and work on it in the dry and in the light.


I'll post up another video once i get the alternator out.


Thanks all, have a great weekend!

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Hi all

Good morning!


So I used that article and removed the alternator yesteday afternoon - very easy job with that link/article.  Its being collected today and hopedfully repaired under waranty.


I did locate a few other issues that I'll have to address at some point, but for now i'll just enjoy the car and use it:


1) Small drip from the bottom of the case where it joins the gearbox- I guess this will be the seal on that often suspect IMS bearing? Bit damp on that specific piece of the case and a few drips each day.

2) I also found a small rubber o-ring just below the alternator, around 10mm width. The O-ring is the Same as the one fitted to the unit i removed which is on the bracket above the alternator. I'm going to check that this bracket/unit item (sorry im not sure of its name at the moment) should have 1 or 2 O-rings, but i think 1 O-ring would be fitted as i dont think Porsche would fit 2! I'll check the part in the parts diagram.  This other o-ring migh have just been dropped from a previous owner/job.

3) The 4 jubilee clips which secure the throttle body to the "Porsche" inlet manifolds  (2 each side) were pretty greasy/gunky at the bottom, really dirty and grimy. So I cleaned these up with some white spirit. Might just be a build up of years of crap and dust, with a bit of seeping of fuel. But something to watch out for now its clean.


Otherwise the engine was just dirty so I've cleaned what I could reach.


I'll get one of my classic videos made tonight if its not to dark.


***Ahsai --- That green connector on the right side of the engine, is just a cover for spade connectors. The wire looks pretty new and goes onto the pump on the right side of the engine, the pump below the hydraulic oil reservoir. The wire goes right behind the actual pulley part. Not sure if its the  aircon or power steering pump.


Have a good day everyone!




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It sounds like the small drip may be a leak in the rear main seal ( RMS).  Not sure how many miles you have but to get to the RMS you have to drop the transmission and it's best to do several maintenance items like clutch, check flywheel, IMS etc. The cost of the labor to get to these items (9-10 hours) is a big consideration and is why it is best to take care of as many items as possible when the tranny is dropped.  If the little drip gets worse, oil saturating your clutch pressure plate is a real possibility. If your MY00 has 100K-KM (60K miles) or more it's probably time.

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1) The drip is not good. Like Kbrandsma said, it could be RMS. However, it could also be the IMS, Either way, you need to drop the transmission to find out. Note s leaking IMS can also be a precursor of IMSB failure.


2) Probably just an old o-ring from previous install


3) That's not uncommon. Usually the AOS cannot clean up the oil vapor 100% so the residual will be accumulated at the bottom of the intake plenum and then leak out to the rubber sleeves.

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Hi guys


Thanks for the response, always appreciated.


The cars on 96,000miles so its pretty high. I dont really have much paperwork on it, just a normal service history for the first 10 years.


The quote for the IMS bearing and seal is £1200, or close to £2000 with the new clutch fitted (a worth option they said). I could possibly do the job myself if i needed to, but I know its much easier with the car up in the air on a hydraulic lifter. I cant afford to pay anyone so for now I'll monitor it and if it does get to a worse stage, then I'll take it off the road until I can get it done.  Hopefully though i can just use it as it sounds good and runs very nicely, with no odd noises. The leak is pretty new (if that helps...!).



Heres a video I took yesterday , with the alternator removed and some of my other toys...!




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Great toys, including the VW microbus!  Nice! 


In the States they sell "Simple Green" which works great for engine cleaning.  Just hose with water, spray on "Simple Green", let set and gently wipe with cloth and repeat.  Not sure what they sell in the UK that would be similar. You may need to push it out of the garage thou to avoid water in the garage.




Also,  make sure you mark your serpentine belt and re-install it in the small rotational direction before removal.  Unless of coarse you plan on installing a new one. New belts are bi-directional but once used they need to be re-installed in the same direction.

Edited by kbrandsma
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Thanks KB - I'll have a look around for something similiar as I want to get it nice and clean :)



UPDATE on the Alternator:

So, I've just spoken to the company (a few times today) who sold me the alternator and they have tested and inspected it and state that its actually ok. They said that they have checked all the diodes and the components  and replaced the bearings as they were a bit worn.  they ran it on their expensive test rig and confirmed it was all ok.


So thats pretty odd. There going to send it back today anyway.   But tonight, i'm going to basically reattach the battery and confirm there is no noise or drainage on that wire on the Jump starter box - just incase its the Starter Motor related? Originally I unbolted the fat wire on that jump point and removed it from the bolt, then engine bay went silent and the current loss went.   Im just thinking - could it be the starter motor if it wasnt the alternator (thats assuming the alternator guys are good at their jobs and it is actually ok/or they fixed it...  :)  ) ? 

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Hi all

Good evening, bit of an update:


So I got home, the note I left for the postman was still on the door and there was no alternator.....so I was a bit pi**ed off and resigned myself to a night watching old X-Files. But then the doorbell rang and the neighbour brought it round! result.


So I connected it upto 12v in the kitchen, just earthing the housing and placing a positive current on the big Threaded pos bolt. No noise or anything.


Then I went outside about 10pm as i just wanted to know if it was working or not. I loosely connected it up to the big power wire and pushed in the Regulator plug. Reconnected the battery and the Hum was still there. I pulled of the regulator plug and the hum stopped. I have the printout here from the "Opal Tester" rig that the guys used to check the alternator; the test rig confirms about 10 things including Leakage Current, Ripple Voltage, Output Current etc, all ok. Its also visually mint and they put in some new bearings to.


So I removed the alternator and took it apart in the kitchen, checked the part numbers and all compatible parts for a 996. Thought I better check incase it was for a later car for example.


I reinstalled it about 1045pm and this time , I really pushed the Regulator connector in hard and it clicked, which it didnt do before. I then turned on ther igintion, reset the windows and turned of the ignition - I made an effort to turn the key all the way to the left before pulling it out, as I read that sometimes the ignition gets worn and things don't Turn off when they should do..... I checked the alternator and there is now No noise....  So I reassembled the airbox etc.


Locked car and still no Hum.


Its to  late to start the car (as its in my garage now) , so i've put it on the trickle charger overnight and will start and check in the morning.



So hopefully it might work. Few possible ideas/conculsions:

*the plug for the regulator was loose and causing some type of issue as maybe it wasn't seated properly.

*the ignition key/system is worn and didn't switch of the regulator part when it should be off.

*me taking apart the alteerntor reg has performed some magic and I've suddenly fixed it through my magic fingers..


Or its going to make a hum tomorrow when I start the car and switch it off.....




Paul !

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PS - A quick question.

I checked the dip stick tonight and its actually 2-3mm Over the maximum mark on the dip- stick. I've not noticed that before, the cars not been started all week and its level in the garage.


Wasn't sure if randomly this could be a cause for my drip between the engine case and gearbox? (RMS seal we think). Just thought that maybe if the engine is like a VW Beetle, the level might be to high and overflowing.  Just an idea for something that I noticed in the dark with my torch tonight.


Cheers, I'm off to bed!

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Hi all

Not had much luck fixing thius fault, so its back out to anyone on the forum who has further suggestions...! :


So, I refitted the alternator and it still hums when you connect it up.


The Regulator wire measures 3.7v All the time, when the ignition is switched off.  If I switch on the Igntion, the voltage goes up to 10.8v on that single pin connector plug (regulator plug). The alternator has been tested to be ok and I just think that the wire should be 0v when the igntion is switched off (if anyone thinks this wire should be live, then let me know please).


I made a video and will post this later.



So extra things i did. I removed the ignition switch, its only a month old and jiust tried it with a screw driver  , I then also tried it with the Original switch and its all exactly the same. I was thinking that Maybe the switch was a bit crap and wasnt fully turning off, so maybe the Alternator was staying powered up. So this didnt do anything when i tried both switches.


I also removed all Relays and the hum remains on the alternator.



Whilst I was poking around at the relays, I noticed a rogue wire, it was cabled tied up and went to the Radio. I removed the carpet trim and actually found a Tracking Device by Motorola. This was heaviuly glued under the CD rack, so I basically removed it all as it was connected up to the loom and using a small amount of power.  But, even after removing this, i'm still showing 380ma drain after powering down the car for 45 mins.



I don't really know what else to do :) . I've analysed the wiring diagram, but can't see anything else to check.



*3.7v constantly on the regulator plug, or 10.8v with the Ignition key switched  on.

*3.5v constantly on the metal alarm horn.

*Both of the above hum/quietly buzz constantly.


Does anyone have a 996 of a similiar year and could check that their alternator is silent without the ignition on? would be handy to know that with the Ign Off, the unit is Silent.




PS - the cars back on an overnight charge again, so at least I can use it tomorrow.

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That's a bummer. Really thought you had it. My alternator (on my '03 996) doesn't hum after key is remved for sure.

Do you still get double beep when you arm the car? That indicates something is not "closed" or not ready. Also, you tried removed all the fuses before but the drain was still there. With all the fuses removed, I would think the instrument cluster is not powered so it shouldn't supply the 3.7v to the alternator either. Seems to me if you unplug the skinny wire (3.7v) at the back of the alternator, the drain will stop?

To further diagnose it, I think you best bet is scan the car with a Porsche scanner to check for any error codes, especailly security related ones.

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My first response was too brief .The wire I was referring to is the skinny one on the alternator .I am pretty sure that it is used as a input signal (terminal 61 ) for the abs/tcs  and should be o when disconnected from the alternator with the ignition key off . Not sure any of this helps but it is not a regulator wire .

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Hi all


Thanks very much for everyone's replies over the last few days - I've just got online and seen them all - honestly much appreciated.


So the ABS light isn't coming on, the regulator thin blue wires is always 3.7v, unless the Ignition key is switched on and it jumps to 10.8v. And of course a constant hum, due to this voltage. If I unplug the blue Regulator wire, the hum goes off, same if I unplug the large fat main power wire.


But I think its the 3.7v on the small reg wire that's bad, I've tested it with a volt meter, its just remaining live all the time.


I've spoken to a friend and his friend does Diagnostics to a high level (has all the gear), so I'm paying him a nominal fee to come over Wednesday night to test it all and to recheck the alternator wire/unit as he also thought it could be Diodes, but the Wire itself shows 3.7v when that's tested, so I don't think the Alternator is feeding current back through it to the dash; the current is coming from the dash down the wire.  I should have tested the current drain in between that thin wire, just didn't think about it at the time. I did test between the thick wire/cable and the "+" jump point (where its bolted to) a few weeks ago and that's where we diagnosed 350ma drawer from that wire/cable.


I don't know where the thin wire goes to once it leave the alternator (except ultimately the dash light), I've removed each fuse (a week or two ago) and the drain remained at around 400ma .



**Going back to some of your responses:


dcdrechsel​ _ I saw "39" mentioned in the wiring diagram, I don't know what this means or is? is it a terminal, block or something  - Once I know what this is, I'll locate the point and check it (if you have any idea what it physically is and where approx it is) ?


Hilux2400 - Thank you for also checking, much appreciated!

Ahsai​ - I don't get any double beep. The car locks at it should do and most things do power down over 30mins, then just stops at around 400ma approx. I'll get the Diagnostics on Wed and hopefully that will Sort why the Alarm Horn always hums and the main Alternator issue :)


kbrandsma​ - I don't know about that, I think the main wires ok, I think its just something not turning of when the keys removed. The terminal 39 could be of interest as this does link to the ABS it suggests in the manual.



If there's any comments, let me know :)  , Otherwise I will check with the man on Wed. I actually can't wait, I really hope he finds something. I'll post once I know.





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39 is a splice point on the wiring diagram .The wire from the alternator  branches (at 39) to the charge indicator light on dash and the abs/traction control .It is referred to as terminal 61 which is positive generator output .It appears that either the dash light or the abs unit is producing voltage  it shouldn't .Unless the wire has somehow shorted to a switchable positive voltage .

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