996 Battery drain and alternator overcharging? Helpful advice welcomed!

[FONT=calibri"]Dear PCGB members, [FONT=calibri"]Can anyone offer me advice with the following issue? [FONT=calibri"] [FONT=calibri"]I went to start my 996 3.4 C2 and the battery was flat, I connected jump leads from another vehicle and it started immediately. [FONT=calibri"]Once running I put a multimeter across the battery terminals and the reading was 14.5 volts so I assumed the alternator was charging properly? [FONT=calibri"]The battery was over 9 years old so before doing anything else I fitted a new one, the car started fine, I ran it for a few minutes then turned it off and left it, after two days of sitting in the garage the car would not start, the new battery was flat. [FONT=calibri"] I removed the battery, recharged it and left it for a few days (off the car), tested the voltage over a few days and the new battery appears to hold charge. [FONT=calibri"] [FONT=calibri"]So now I am thinking maybe there was nothing wrong with the old or new battery? and I tried some more tests: [FONT=calibri"] With the new battery charged and re-fitted I used a multimeter to measure the drain, from cold with the car turned off the reading was around 0.04 Amps (I understand the vehicle can take an hour to ‘shut down’ properly) but from what I have read this reading sounds sensible? [FONT=calibri"] [FONT=calibri"]I re-connected the battery and ran the car, as before the reading at the battery terminals was 14.5 volts, but this time I left the car running and as the car came up to temperature the reading at the battery terminals shot up to 17 volts. With the car turned off I again tested the battery drain which was now reading was around 3.35 to 3.90 Amps. [FONT=calibri"] [FONT=calibri"]Sounds like an alternator related issue?, [FONT=calibri"]I have read a various information and read things about voltage regulators and diodes etc but most things I have read relate to the alternator undercharging? Mine seem to be over charging when the car is warmed up? And why does the battery discharge but only appears to show the drain on the multimeter when warm? Are these two issues related or one of the same? [FONT=calibri"] [FONT=calibri"]Any advice would be really gratefully received, as you can tell from the above I am certainly no expert! I am just trying to understand the basics before looking at my options to repair it; Are my tests sensible/valid, [FONT=calibri"]Any more tests I should try?, should I replace parts? voltage regulator? Are the diodes part of the voltage regulator, can these be replaced etc. Is it false economy or difficult to replace these parts should I go for a new or reconditioned alternator? Right now I am thinking of removing the unit and taking it to an auto electrician, as I say a[FONT=calibri"]ny advice would be really gratefully received . [FONT=calibri"]Thanks in advance [ ] [FONT=calibri"] [FONT=calibri"] [FONT=calibri"]Kind regards [FONT=calibri"] [FONT=calibri"]Mike

Battery drain is a common complaint we see. A few pointers from our experience: We normally say a drain of 0.25A is the upper limit and should give about 2 weeks life on a fully charged battery. Alternator voltage, measured at the battery, is normally between 13.25 and 14.5V, depending on health of alternator and associated wiring. We use a clamp in the earth lead to measure current. We shut the car down and even close the frunk locker latch. Wait up to 30 mins for the drain current to drop. Any of his helpful? Kind Regards Lee Jones

40mA is normal, but if the drain is 3.5-ish amps, it sounds very much like the diode/regulator pack on the alternator has failed, which is a fairly common problem. You can replace the regulator - it is a Bosch part, and about £25-30ish. There's quite a good DIY here: http://forums.pelicanparts.com/porsche-996-997-forum/408495-alternator-repair-regulator-replacement.html Bosch Part number: F 00M 145 225 (Replaces F 00M 145 350). Porsche Part No: 000.043.206.37.

Thank you for the advice so far, appreciated, here is an update... I have now replaced the regulator with a brand new genuine Bosch part (£27 from APD), quite a simple job although the alternator is a bit tricky to remove, the link that Richard provided is extremely helpful (Tip, watch for the small rubber o-ring if you undo the pipe above the alternator to provide a bit more room). Re-connected the battery and ran the car, the reading at the battery terminals is now 18volts (immediately from cold) and with the car turned off I tested the battery drain which was now reading was around 5 Amps. So unfortunately changing the regulator unit does not appear to have solved the overcharging/drain issue, also odd that I am getting different readings and the car does not need to be up to temperature to detect the overcharging/drain problem. I feel it has been useful to eliminate the possibility of a faulty regulator, but a bit frustrated it has not solved the problem? Any further advice would be greatly appreciated, any thoughts on what I should do/try/replace next? Kind Regards Mike [FONT=calibri"]

You will have to start removing the fuses one by one, whilst watching the current drain. sws

What happens to the drain if you disconnect the alternator? That would rule it out of the equation. You should measure the drain after 30 minutes with the car locked, as there are some fairly heavy drains that don't shut down until that time has passed. Here is a document which explains the procedure. (Bear in mind it is for the pre-facelift - there is a different document for MY2002-on). After that, it is a case of pulling fuses as has been said, and maybe looking for an old tracker or other permanently wired device. Download

I think this is not a diy job to do as running a car on 18v even for a short time ,will start to damage the ecu and other components it could be very costly ,you need to get car to a auto electrician ,and explain the situation to him.in my view you need to get the batterys tested by doing a load test,as the 18v could indicate the batterys have had it,it could also be faulty earth returns on car or high resistance in earth returns ,and alternator/regulator could be faulty,have you got another voltage meter to check the one you are using or a known dc voltage supply to test on,(on a car you should only see about 13.8-14.5 volts when charging)try taking batterys off car and charging them with a battery charger connect a meter to them when charging and note the voltages. batterys may have been damaged by car earlier on.to look for what is draining the battery a dc clamp meter would be needed or a 10 amp ,amp meter connected in series and then start pulling fuses out ,also have you checked the resistance of the windings in alternator windings should be balanced, i work on engine electrical systems for ford and jaguar

[FONT=arial"]Thank you for the advice so far, appreciated, here is another update... [FONT=arial"] [FONT=arial"]Since the alternator appears to be showing an abnormally high charge reading I have not tried anything that involves running the vehicle. [FONT=arial"] [FONT=arial"]I have tried a few more tests with the battery temporarily re-connected (and waiting a while for the vehicle to 'shut down'). [FONT=arial"] [FONT=arial"]With the alternator fitted to the vehicle the battery drain reading settles at 4.7 Amps (too high?) [FONT=arial"] [FONT=arial"] If I remove the alternator completely from the vehicle the reading drops to 0.02 Amps (sounds ok?) [FONT=arial"]From here I have taken the alternator to an auto electrician and explained my findings. [FONT=arial"]The [FONT=arial"]auto electrician has suggested this could be two issues, the overcharging issue could be related to the voltage regulator and the battery drain issue could be related to the voltage rectifier. [FONT=arial"]They have bench tested the unit and confirmed it is faulty, they the think voltage regulator is bad (but say the [FONT=arial"]rectifier seems ok). [FONT=arial"] [FONT=arial"]However: 1) I have already replaced the regulator with a brand new Bosch replacement and 2) the [FONT=arial"]auto electrician is suggesting the [FONT=arial"]regulator is only related to the overcharging issue, if so where does this leave the battery drain issue? Having discussed this with them they propose replacing the [FONT=arial"]regulator first and reviewing the situation, my fear is the cost will escalate and the issue may not get resolved. [FONT=arial"] [FONT=arial"]The [FONT=arial"]auto electrician company have been very helpful but I am not confident with this as a way forward. Does anyone have any further thoughts on this? Hopefully I get this sorted and maybe this information can help others in the future? Kind Regards Mike

If it helps I fitted a new Bosch regulator to my spare 996 alternator. It's still in my garage unused. If you want to try fitting it to your car to see if it cures your problems then by all means. You can buy it if it works at 'mates rates' I'm in London.

Hello, I have an update which I hope concludes this story and may possibly be of help to others experiencing a similar issue. First off I would again like thank all those that have helped including the extremely kind and generous offer from Rodney (above) much appreciated, shows what great people we have in the club. Following the all the various things mentioned above I decided to order a replacement used alternator and experiment with that. Since fitting I have performed a few tests: -Day 1, the alternator showed a charge of 14.50volts from cold with a battery drain of 0.11Amps immediately after turning the car off, after waiting 1hr the drain dropped to 0.02Amp to 0.03Amp. Battery had been sat on the workbench for a few weeks but showed 12.62volts and started the car no problem. -Tested a few days later the alternator showed a charge of 14.46volts from cold and the battery had 12.49volts and started the car no problem. -Tested a few days later the alternator showed a charge of 14.48volts from cold and the battery had 12.46volts and started the car no problem. -Following the tests the car seems to start no problem and the charge on the gauge in the car looks fine. So from what I can see the replacement alternator appears to be pushing out voltage in the correct range and the battery is not being completely drained within days, the drain I have measured looks sensible? So fingers crossed it looks like the alternator was causing the issue. The actual issue with my original alternator remains unsolved but I have returned the voltage [FONT=arial"]regulator to Bosch for comment. [FONT=arial"]Now time to go and enjoy using the car again! [FONT=arial"]Mike

Thanks for the update Mike, It's always good to know the outcome these issues. enjoy Andy