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FYI - Low Voltage Issue at operating temperature

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I want to share an experience I had with my 2002 996.  For the past several months, after a cold start, my initial volts held steady at 13.8v indicated.  As I drove around, I had problems with the voltage dropping to 12.5-13 volts without any accessories turned on after the car reached operating temperatures ~180 degrees.  Once I turned on the A/C, the volts dropped below 12.  This has left me having to jump the car a few times.  First thoughts typically range from a bad battery, alternator to starter.  Like many, I headed to the local parts store to have the battery, alternator and starter tested - all passed.  Second reaction is to clean the terminals on the battery and grounding points, yet the problem persists and leave a few scratching their heads.  I checked voltage drops between components, I checked for AC volts to see if I had a bad diode, and recharged my battery.  In my research, Porsche 996/997s have a well known issue within the community that the positive wiring from the junction box to the starter to the alternator tend to go bad prematurely - corrosion typically seen on the starter wiring.  What happens as I understand it is that when the car is cool, the wire coming off the starter is cool and electrons flow fairly easily (note the initial 13.8v at start up).  As the car heats up, so does this wire and in doing so, the heat coupled with the corrosion reduces the overall voltage/amps going to the alternator making the alternator operate sub optimally thereby reducing available voltage at operating temperatures (12.5-13v).  When the accessories are turned on, more volts/amps are needed, but the alternator is struggling to put it out while maintaining the average 13.8-14.2v seen on healthy cars.


I pulled the alternator and starter to have them tested independently removed from the car.  In doing so, I visually inspected the wiring harness connecting these components.  As I did this, I noticed pretty bad corrosion on the wire coming off the starter as you can see in the pictures.  I knew immediately what my problem was given an all 'pass' on my battery, alternator, and starter at the parts store.  I ordered a replacement.


Even though my problem was pretty obvious after seeing the wire, I recommend getting the individual parts tested as they will be out anyway when replacing the wire.  It's still good practice to clean all the grounding points (engine to chassis, battery terminals, etc).


I hopes this helps others having similar problems.





Edited by Hobbes
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Just a quick update - I put in the new Y cable and it fixed the low voltage issue I was having.  If you have a low voltage reading, check the cable before buying new parts.


The first picture is the voltage reading prior to fix.  Second picture is after the fix (under load - A/C), Third picture is with no load.


Good Volt.JPG


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Good to hear. I have a similar issues and what sucks is, I replaced my Y-cable about 6 months ago and my alternator about a year ago. I am also getting a low voltage at operating temperature. When I start the car, it will be about 13.5 volts. As I drive it, the voltage will drop to 12.6 ish. AC on or off, doesn't matter. I replaced the battery (3 years old) and the voltage regulator last week, but the problem persists. Any ideas? I have a '98 C2 coupe if it makes a difference.

Edited by longrowe
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