996 Electrical Problem- Bad battery or alternator?

Need some help from the experts. I am out of town. My wife recently left the key in the ignition overnight and we had a dead battery. She was able to start it using an external battery pack and the car has worked fine the last couple of times she used it. Today she noticed on the way to the gym that the voltage was below 12. She never got any warning lights. When she came out of the gym class the car would not start. She was able to start it with the external battery pack, but the car died after she removed the battery pack. She tried it again and the car continued to run. She tried to drive it and it drove forward but she had to let off the gas because another car pulled out in front of her in the parking lot and it dies again. My guess is the alternator is failing and need to have it towed to the shop. I don't know how old the battery is. Thanks for the help...

Could be the voltage regulator. Make sure they test that first. It's much cheaper than an alternator. $45 vs $400

Check the battery for a short too. There is a long thread about how to check the alternator output. I followed it to ID a bad alternator a few years ago.

It is just the battery. Go to any auto parts store and they will check it for you. Buy a new battery, install and you are done. Don''t make this complicated. An automotive battery does not work right again after being fully discharged. They are not deep cycle batteries.

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Thanks...The reason I questioned just the battery is every time i have had a battery issue in the past, once the car started it ran fine. If it didn't start the next time then would look at replacing the battery. Replaced the battery and car is running fine. Voltmeter is right at 12 on the dash. Will keep an eye on it to make sure it is charging. Thanks again..

Firestone sells interstate batteries. Assuming she can get it started and drive it to the nearest Firestone, she will be golden in 30 minutes.

Did you just replace the battery yourself and not have the charging system checked? Sounds to me that your new battery has 12v and the alternator is not putting out anything. Should be at about 14 with the engine running.

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Yes. The battery was 6 years old, so started there to at least get it driving. Now that I have the car at home can do some troubleshooting and determine if it needs to taken it to the shop. Was going to start at the alternator and researching the best/most accurate way to check that.

Check Alternator: Use a multimeter to measure voltage while the engine is running; either at the rear jump point or at the battery. Should be 13.4 to 14.7 Volts. If so, it's charging. If less than that, the alternator is not charging. If more than that, then the regulator on the Alternator is bad, and it will kill your new battery quickly. BTW, if you need a new alternator, the 996 Bosch part is AL0812X ($500+!!!). But the 997 part, AL0815n (a 15 Amp version, $365 from summit racing) is exactly the same, and fits exactly the same.

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Checked the voltage at the jump point...before and after engine start and running at idle...both are right at 12 volts. I have seen some recommend changing the voltage regulator first. Could this be a bad voltage regulator or definitely the alternator?

Mine stopped charging suddenly last July. Luckily I have a 986 that has the same alternator. Removed that voltage regulator and put it in the 996. That worked so I ordered just the regulator. Think they are about $45. It also could be a bad cable or connection point.

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How long did that take you? Pretty easy job?

It's a pretty tight fit. Although the 986 is much tighter. 24mm wrench or socket needed. While the belt is off might as well replace it. Check the idler pulleys. Now I could get it out in 10 minutes. Here is a pretty good write up. I was never able to get the bushing out as they describe. I used a small prybar to get it out of the upper mount. https://www.pelicanparts.com/techart...Alternator.htm

If you are replacing the alternator there is a cable, I believe to the starter, you should replace at the same time, it corrodes and causes starting problems.

**Make sure you check the �Y cable� and grounds - clean and tighten them as well. Make sure you always lock the car when not driving it, and if leaving it un-driven for a week or more put it on a battery tender� your new battery will last many years.

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Thanks. Not familiar with the "Y cable"...where is it? Any photos that show its location?

#21 here http://www.autoatlanta.com/porsche-p...section=902-05

Well...I made it this far, but now that I have the bolts off the alternator I can't get it out. I started to remove the piece on the bottom, but coolant started to come out so I retightened. Any ideas on the best way to remove? Disregard..I figured it out.

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I knew someone with a smarter brain would know what that cable is called On my 996 the alternator failed, producing only around 12 v and the Y cable was corroded. I replaced both. Good idea to do while you have the alternator out. Getting the alternator out was a knukle-scraper. Seconds on the battery-tender. I have a permanent connector on my battery that simplifies attaching the tender, just plug it in.

Well I am not sure if I broke this line trying to wrangle out the alternator or this was already broken. Not sure what it is or how to replace. Any ideas? Thanks!

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It's a vacuum line. They get brittle with age and temp. You can get a little rubber slieve and patch if you don't want to disassemble a lot of the engine parts.

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ok, thanks. Can I get the rubber sleeve patch at the autoparts store?

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Good idea. The Y cable or at least the attachment to the alternator doesn't have any corrosion. Looking back there the starter looks relatively new, so guessing when the previous owner replaced the starter they also replaced the Y cable. How did you access the other side? Also, how did you mount/wire the battery tender? Definitely am interested in doing that. Thanks

I have a battery maintainer that I bought at AutoZone. Simple because it has a cigarette lighter plug. Pull in the garage and plug the connector in the cigarette lighter. Done. The cigarette lighter is still active even with the car off. No messing with wires or clips under the frunk lid.

I attached a permanent battery tender harness to the battery terminals. I tuck it out of the way when not in use and cap the 2 prong connector that goes into the rest of the harness leading to the batter tender. I do remove the plastic battery cover to connect up the tender. I don't trust the cig lighter receptacle. I had one short out in my 944 a long time ago. When charging the 996 I leave the frunk barely closed (enough to make sure the frunk light goes out), but not latched shut.

Took the alternator to AutoZone and it failed their tests. I ordered a reman Bosch from Pelican Parts for $388. Hopefully that will do the trick.

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Good job, great progress! There is a picture in this linked thread of the vacuum line routing. If you have the Porsche Sport Exhaust, there is actually an independent set of vacuum lines on the passenger side of the engine, but this link has the basics, including your broken line. https://rennlist.com/forums/996-foru...l#post14216767 As you can see, your broken line goes to the back of the rear intake cross-over. To replace the whole line, you have to remove the throttle body, and remove both intake cross-over tubes; a PIA. At that point, you would probably want to consider replacing all of the vacuum lines, as you'll be able to get to most of them at that point, and they are all brittle. Or, you might save that for another time when you feel like taking apart more of the top of the engine. BTW, if you're trying to trace the lines in the linked picture to your engine, the line going to the "to SAI one-way check valve" is the silver cylinder/canister just visible in the back of your image. The larger SAI tube goes to it.

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Great info. Thanks for sharing. I got some rubber hose at the auto parts store and basically used a four inch section and pushed part of it over each segment of the broken line. Hopefully it works! Replacing the entire line looks like a bigger job than I am wanting to take on at this point. However, maybe it wouldn't be too hard...just tedious to remove the throttle body, crossover tubes, etc.

There is definitely a snowball-effect of "while you're in there", but since this was an unplanned repair for you, so I would stop at that point too. BTW, there is about a 50% chance that you will break the coolant fitting (99610622652) before you are done here, it's notorious. There are metal options for replacement ($5 0 Rauch & Spiegle , or $25 URO). As you have time to plan maintenance, you might think about what you plan. Generally there seem to be two approaches. (1) Don't replace anything unless it breaks, why waist money!?, or (2) I might as well replace a few things "while I'm in there"; I don't want to take this apart again! Last winter I dug into the top of the engine. Replaced AOS with Porschetech3's UAOS, replaced fuel injectors, replaced all the vacuum lines, replaced the starter/alternator Y-cable. Some people go so far as to replace the oil cooler gasket, or even the coolant tank. I also replaced the oil fill tube (it cracked) and the coolant fitting (above, it cracked on me) [old plastic! Agh!].

I did much of the same as above, replaced everything that needed, or would someday, when i had all that out. Esp plastic stuff, and replaced some plastic stuff with aftermarket metal, It's just a pain to get back in there, unless you are a masochist, or double-jointed, like Porschetech3 is (not sure which) So re the infamous Y cable. The corrosion happens in the Y, not at the ends. And you really cant see it easily. You can test resistance, but sometimes better to replace so you never have to worry. Porsche released an improved cable a few years back that fixed that problem, I believe. The new cable cost me $100 back in 2018 from the dealer. Chasing electrical issues can be a real PITA.

Sorry CTIIpilot, I don't know why we're piling on your thread. But while we're sharing information on things that can cause voltage/starting issues, let's talk Y-cable! My old Y-cable on the car: That doesn't look too bad, right? The rubber is only a little cracked. It falls apart on removal. Oh, that's not good. And the lower wire was loose in the crimp from corrosion. No wonder I had hot-start issues.

To replace the Y cable did you have to take out the throttle body and cross-over tubes?

I had everything off, but only because I was doing alot of other work at the time too. The cable route is only clipped in one place, which you can just barely see in my first photo off to the right. I don't know how well you can unclip that with only the alternator out. The other tricky part is that when you buy a new one, it will come with the entire Jump-point box fixed on the end, which means you can't guide the cable between the AC compressor and the Intake manifold on the right side. There is another thread on here somewhere talking about how to install this wire.The best advice I got from that was to soak the new cable jump-point end in really hot water. It will soften the plastic, and with some gentle, gentle, persuasion (with a flat head screwdriver, re-heating as needed) you will be able to pull the cable lug out of the jump-point box. Then you can thread the wire from the starter back to the alternator (easy) and to the jump-point (harder). I did remove the jump point box, because my AC compressor was still in, but everything else was pretty open, so others would need to chime in.

Actually the cable goes between the AC compressor and the Intake manifold. I think with the throttle body and front cross-over on, you would have a rough time getting around behind the AC compressor. But, FULL DISCLOSURE, and a reason I'm not too helpful with the new cable installation: I followed the advice of another thread, and used aftermarket cables from BatteryCables USA ( https://www.batterycablesusa.com/ext...ery-cable-bulk ). They are SAE rated, can be much higher gauge, and are better sealed. https://rennlist.com/forums/996-foru...l#post16849771 That thread doesn't have any detail, so I wouldn't recommend this approach without time to think it through and to plan everything out. I ran one from the jump box to the starter (27" 0-AWG RED. 5/16 straight lug to 5/16 90deg lug) And a separate wire from the jump box to the alternator (27" 2-AWG RED. 5/16 straight lug to 5/16 straight lug) Fitting them all on the pole at the jump box required installing a longer bolt, (EDIT: McMasterCarr, Zinc-Aluminum-Coated Alloy Steel Socket Head Screw, M8 x 1.25 mm, 30 mm Long), and some aluminum spacers (Aluminum Unthreaded Spacer 3/4" OD, for 5/16" Screw Size, 1x 3/8" long, and 1x 3/16" long) Custom cables next to old Y-cable New cable routed same as the old y-cable. A socket head bolt snaps into the base of the jump-box. So I got a new, slightly longer one, with some aluminum bushing/spacers to keep everything tight on 3-cables, instead of the original 2. Aluminum is close to zinc as far as galvanic index, so between the zinc plated lugs, zinc plated bolt, and aluminum spacers, it shouldn't corrode much. New larger, heavier lugs at the original jump-point. I had to cut the opening at the bottom of the box slightly larger, but it does latch closed as it should. All done.

Great photos and write up. I did the "hot water to remove the block" approach. Worked fine as I recall. But that was 4 years ago and many projects ago. But you can search and find lots of threads.

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Try checking it with a multimeter - if the engine is running you should be getting around 13 to 14 volts. If it's lower than that; It�s probably the alternator. But usually the batt icon appears.

Got the new alternator from Pelican Parts and have it installed. Anyone know what the torque values are for the two bolts that hold the alternator in place or where I can find them? Thanks!

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Have you downloaded the Work Shop Manual pdf yet? Or maybe buy the Bentley Service manual? Lots of great in those. Alternator to engine block: The M16 bolts are at 48 +-4 ft/blbs M10 at 33 ft/lbs

Thanks for the info! Where is the best place to download the manual?

Success! New alternator is installed and working as advertised. Really appreciate all the help on this thread for me to get this project complete. If someone is visiting this thread in the future and thinking about taking it on- my take is this was actually pretty easy (even for a car mechanic novice like me). The hardest part was the access and getting the alternator in and out. I replaced the belt as well as the air filter while I had it apart. Gives me confidence to take on some more projects in the future. Very rewarding and looking forward to doing some more work on my 996. I bought it last summer in Colorado and immediately drove it to FL. I have had no problems with it and use it as my daily driver. I love driving it and very happy I bought it.

You should expand your library with a couple of books if you want to take on more projects. The Bentley manual, the 996 Essential Companion and the 101 Projects for Your 996. The last one is a compilation of Pelican articles, handy to have in one book. The Companion has lots of great info on the 996 model and variations, not so much in mechanical how tos. You'll have all the info you need, along with bookmarking this web site, to be ready to take on whatever your car throws at you. Plus the WSM. You can search this forum for links where to download that.

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I wish I had known this, just replaced mine and I was shocked at the price tbh.

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Great! The book recommendations above are great. I'm just a home DIY'er, but the Bentley manual is a staple on my workbench. I ran across that in another old thread on here somewhere. The Bosch sourced AL0815n on the right, original 996 part on the left. It's 150A vs 120A, but they both weight exactly 6.7 lbs (someone said the 997 one was lighter, it isn't.)

Well I found a rubber part on my garage floor that says "Made in Germany" so I am guessing I missed a step. Going back a watching a couple of videos, I think this is a rubber spacer for the alternator idler pulley bolt. Can you guys confirm? I pulled it off and I currently don't have a spacer there. I don't recall there being one there when I pulled it off, but it could have just fallen to the floor. Thanks for the help.

Forgot to recommend you also download the Porsche parts manual, you can look at the diagrams and that helps tell you what parts go where. Plus it gives you the Porsche part numbers when you need to order something. Probably a good idea to put it back in A successful job is one where you don't end up with any extra parts, or come up short on parts Here's the link. https://www.porsche.com/all/media/pd...96_KATALOG.pdf

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Thanks for the link for the repair manual. I did a search of the part number: 999-703-478-40 and came up empty. I did a google search and states it is a grommet is for the air handler. I think that is what it is and I can see where there were two. Not sure where the other one went.. I was confused because one of the videos I watched referred to a separate spacer behind the idler pulley. I don't have that.

I got so tired of those coming off and falling down to the pulley area on both cars, went ahead and ordered 4 new bushing and urethane glued them to the body. never had an issue again.

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As long as the pulleys line up and spin freely you are fine. That is a spacer on the back of the pulley.