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Silver_TT

Electrical issue with 996 -- brake distribution, PSM/ABS failure, batt

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2002 Carrera 4S. I did a search and didn't see these exact symptoms simultaneously.

See attached picture. I was driving at 5k RPM in 3rd when the power of the car was suddenly reduced (by the computer I believe) and the console beeped displaying the following 4 checks: 1. Brake distribution 2. PSM failure 3. ABS failure 4. Battery -- also, as you can see in the pic, the battery voltage meter is maxing out. When I disengage the clutch from the engine the voltage drops some (and the brake/ PSM/ ABS messages go away and are temporarily ok) but is still running significantly higher than what I'm used to seeing. Could this high voltage be damaging to the electronics system? Presumably there's something going on with the voltage regulator. Does the ABS/ PSM turn off automatically for saftey when there are voltage spikes?

My battery is an Interstate and is ~ 1yr old. This seems to me like the alternator (possibly the voltage regulator). I realize it would be better if I had a Durametric to hook it up to and get the exact error codes off of. That may need to be done to properly diagnose what's going on here.

Thanks in advance for any help/input.

Cheers,

Alex

post-72654-0-67161400-1342404770_thumb.j

Edited by Silver_TT

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After letting the car sit an hour, I just took it on a short drive and the battery voltage is now between 12 - 14 and constant as it normally is. However the battery light is still on. Anyone know if this means the computer is currently detecting an issue or if instead this is a light that can become "tripped" (like the airbag light) and just needs a Durametric to be reset. I'm still assuming there's something flakey going on with the alternator.

Thanks in advance for any ideas.

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Without the reading the codes, it is always a bit of a crap shoot; but your car is displaying the type of faults often associated with either a battery or alternator issue. Get the car scanned for codes, have the battery load tested and check the voltage of the alternator under load, you could just have a voltage regulator on the way out (pretty common).

Edited by JFP in PA
  • Upvote 1

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Thanks for the response, JFP.

I ordered a Durametric this morning. While not completely ruled out, I'm guessing it's not the battery since I just replaced it late last year. I will perform the proper diagnostics but assuming this is the voltage regulator, I understand that this is not sold under a separate Porsche 996 part number. However, I saw the link below on Pelican which says you can buy Bosch part# F-00M-145-225. I was wondering if following this procedure is considered good practice (not replacing the whole alternator if it's just the voltage regulator, which you say is not uncommon) or if it would be better to replace with a new alternator. My vehicle has ~ 90k miles and I believe is on the original alternator. I asked the indy shop I use and the guy at the front desk said he thinks they usually replace the whole alternator when the voltage regulator goes.

http://forums.pelicanparts.com/porsche-996-997-forum/408495-alternator-repair-regulator-replacement.html

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Just about everyone on Earth, except for Porsche, sells the voltage regulator; it is a common inexpensive part number to Audi, VW, MB, and even some Fords. Replacing the regulator is usually an easy fix for many alternator issues short of bad bearings, and one Hell of alot cheaper as well. If nothing else is wrong with the alternator, just do the regulator.

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Replaced the voltage regulator, all is good now. $30 for a new voltage regulator...or $300 for a new alternator. Tough choice, eh?

As the Pelican link above says, the original Bosch part# was F-00M-145-225. I bought a Bosch VR-IB225N from Ibc Automotive out of California, which they said was interchangeable and it was. This part is interchangeable with a ton of German cars including VW, Mercedes, Porsche, etc.

It's always best to have your alternator tested if you have this issue but the tell-tale sign to me was that I was seeing the voltage on the console show all sorts of crazy readings. It would jump around... then drop... then spike when I accelerated. Definitely not the constant, steady voltage readings I get under normal operation.

Conceptually this DIY is a 1 / 10 on a scale of difficulty. Getting the MAF off is cake, and getting the belt off is simple (needed to buy a 24mm socket for the tension pulley--also needed a 14mm or 15mm for the alternator). However, once I got to the alternator I had a lot of problems getting it off because of the bushing in the rear flange. Getting it in and aligned so you don't strip the long bolt with the pulley on the right-side of the alternator is also a total PITA. Be sure to follow the instructions closely when taking the alternator out and whack that bolt with a hammer (use a buffer as not to damage the bolt) after a few twists out. Getting the alternator in/out was by far the hardest part of this procedure and probably made it more like a 5 / 10 for me. Had it been easier to get that in/out, I would have had the whole job done in 30 minutes or less. Instead I ended up spending at least a few hours...

Thanks to JFP for the advice. It was dead-on and you saved me a few hundred bucks, which I greatly appreciate (hey, I own a 996, I'm a value hunter :)).

Edited by Silver_TT

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Replaced the voltage regulator, all is good now. $30 for a new voltage regulator...or $300 for a new alternator. Tough choice, eh?

As the Pelican link above says, the original Bosch part# was F-00M-145-225. I bought a Bosch VR-IB225N from Ibc Automotive out of California, which they said was interchangeable and it was. This part is interchangeable with a ton of German cars including VW, Mercedes, Porsche, etc.

It's always best to have your alternator tested if you have this issue but the tell-tale sign to me was that I was seeing the voltage on the console show all sorts of crazy readings. It would jump around... then drop... then spike when I accelerated. Definitely not the constant, steady voltage readings I get under normal operation.

Conceptually this DIY is a 1 / 10 on a scale of difficulty. Getting the MAF off is cake, and getting the belt off is simple (needed to buy a 24mm socket for the tension pulley--also needed a 14mm or 15mm for the alternator). However, once I got to the alternator I had a lot of problems getting it off because of the bushing in the rear flange. Getting it in and aligned so you don't strip the long bolt with the pulley on the right-side of the alternator is also a total PITA. Be sure to follow the instructions closely when taking the alternator out and whack that bolt with a hammer (use a buffer as not to damage the bolt) after a few twists out. Getting the alternator in/out was by far the hardest part of this procedure and probably made it more like a 5 / 10 for me. Had it been easier to get that in/out, I would have had the whole job done in 30 minutes or less. Instead I ended up spending at least a few hours...

Thanks to JFP for the advice. It was dead-on and you saved me a few hundred bucks, which I greatly appreciate (hey, I own a 996, I'm a value hunter :)).

Awesome report and great conclusion!

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Here's a picture of the culprit. This was the original voltage regulator taken from my alternator and replaced with the part I mentioned above (that also works in various other cars like VW, Mercedes, etc).

I can't say what caused what, but it turns out that my wiring harness that runs from the alternator to the starter to a junction block was also bad and was causing resistance when it heated up (I believe there's a TSB related to this). Thanks to JFP in PA who was a huge help tracking this down and told me that these two parts can sometimes go out together. I saw Logray and some others had this problem too in the past (see link below) so that was helpful too. It's been 100+ degrees F here for the last few weeks so it's not surprising that if it was going to happen, it would happen now.

http://www.renntech.... guage harness

Also, FYI, in response to my own question above: The "Battery / Generator" warning message and accompanying battery light on the console goes on when the computer detects that the voltage is too low. It's not something that is "tripped" and it will go off once the battery is recharged and the alternator issues are fixed, therefore keeping the battery charged. This can also happen if you leave your light on or door open in the car too long and it drains the battery. Just take it for a spirited drive to let the alternator charge the battery or hook the battery up to a charger if it gets too low to crank the starter.

Thank you!

:renntech:

post-72654-0-80397600-1343160675_thumb.j

Edited by Silver_TT
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To be thorough and follow-up (hopefully for good), let me offer the following. Hopefully this helps anyone with the same problem in the future. Since the people on this site (JFP in PA, etc) were so nice to offer their time to help me, I think it's the least I can do.....I really, really appreciate everyone that helped me through this issue.

Everything I said above is true. Replacing the voltage regulator did get the voltage to stop bouncing around and I stopped getting PSM/ ABS failures, etc. It made the car drivable again. However, on short distance trips to run errands I noticed the battery was slowly draining. I was able to keep the car operable by hooking my car up to my C-Tek 7200 charger/maintainer at night. In the process of all of this I had the wiring harness (the one that goes from alternator -> starter -> junction block) replaced because there was some resistance as you traced its path from the alternator. I believe there is a TSB on that and I understand that the issue is so common that most dealers keep the part in stock. However the battery was still being drained after all of that. I was so confused since I had the alternator tested at Auto Zone and their diagnostic said it was fine. Indeed, electrical problems can be difficult to track down.

It turns out my alternator was bad and I think it was subjecting the voltage regulator to high stress and caused it to fail. This is the chicken-and-the-egg problems so I don't know what caused what, but that's my best guess. As I would find out later, my alternator was working just fine at higher RPMs so highway driving was just fine. However, at idle RPM it wasn't working 100%. This explains why the short trips to run errands were problematic. I guess another moral of the story is don't always trust Auto Zone's alternator testing equipment. I'm sure it will tell you if your alternator is completely dead, but it certainly didn't catch mine which was half-working.

So I ordered a new alternator from Vertex. Part is 996-603-012-02 for my 2002 C4S manual transmission. Cost was $375 total shipped (after $200 deposit to return old core). Replacing the alternator is one of the easier things to do on this vehicle as long as you follow Loren's DIY and uncsrew the bolt just slightly and tap the bolt head with a deadblow hammer to loosen the back bushing on the alternator from the engine flange.

Edited by Silver_TT
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