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I'm guessing the alternator is shot, but anything else to check before I bite the bullet?
Any diy for a replacement?
Thanks!
Certainly not clear to me your car's alternator is shot based on what you posted.
In the recent bit of hot weather we've had I notice that after starting my Turbo the battery voltage is lower than it was when it was started in colder temperatures and after the engine runs the voltage level drops faster than it did when it was colder. Lead/acid batteries like the warmer weather.
Sunday starting out with the ambient temperature at 104F I started the engine and noticed the battery voltage gage needle was not up to nearly 14V as has been the case previously. And after a bit of driving the voltage level was down to just a skosk under "13V".
The engine ran just fine and this with the A/C on to keep the cabin at the selected 72F temperature even though I drove through at various times anywhere from 104F to 108F ambient temperatures. (Now you know why I run 5w-50 (not a type for 15w-50!) oil. It gets blasted hot here.)
The alterator is only going to give the battery as much voltage as it needs to top it up after an engine start then it is going to reduce the amount of voltage it supplies to the battery to avoid cooking the battery.
In the meantime though the alternator is putting out electrical power that supplies the rest of the car's electrical needs.
The engine controller and other controllers are very sensitive to low voltage and if the alternator wasn't putting out enough electrical power you'd know it.
I live in AZ I always watch my gauges. In winter months my car always starts at around 14v then levels 13.8ish Radio and radar detector only .Summer months starts around 14v then levels off with my ac/radio/radar detector it hovers around quarter inch above 12v on hot 105+ day. when I do my two minute cooldown's 30 seconds before I turn it off I turn off all accessories and my gauge or go back to 13.5v before I shut my car off. Keep in mind it takes a 30 mile drive for alternators to charge our batteries so if your battery wasn't fully charged before that would account for fluctuation. Also helps to keep a battery maintainer so it's always topped off, short drives kill our batteries. Btw for reference points I've had my car for eight years and on my second alternator since I've owned it. Today's supposed to be 120 if I drive my car today with all the accessories on it would be in the low 12s.
AC, radio. i turned them off also and the voltage did not go up. On my drive this morning my voltage was fluctuating between 12-13 on the gauge.
It is quite possible your battery might be on the way out.
Fully charge your battery with a charger and then bring the car to Autozone and have them perform a free and complete charging system test. It is the best way to track the root of the issue.
The Voltage Regulator issue is well documented as the cause for low/erratic charging voltages. I swapped mine out and it cured all my charging problem regardless of load. Give it a shot.
Anything below 12.7 volts when running (verified with a multi-meter directly at the battery terminals with the car fully warmed up and engine running) is not normal. If this is the case with your car, it is very likely that you need to replace the alternator's voltage regulator. When I replaced mine, I did some research and found out that the 996TT-specific regulator has been superseded by Bosch with part #F00M144136.
I can't believe no one has asked you to check your grounds. Although it's usually a great guess that the alternator needs replaced but, checking grounds is free. Even with the AC on you should be above 13 volts. Once your voltage evens out to 12v the battery will become drained.
Anything below 12.7 volts when running (verified with a multi-meter directly at the battery terminals with the car fully warmed up and engine running) is not normal. If this is the case with your car, it is very likely that you need to replace the alternator's voltage regulator. When I replaced mine, I did some research and found out that the 996TT-specific regulator has been superseded by Bosch with part #F00M144136. Here's the one I installed that has been working well.
I can't believe no one has asked you to check your grounds. Although it's usually a great guess that the alternator needs replaced but, checking grounds is free. Even with the AC on you should be above 13 volts. Once your voltage evens out to 12v the battery will become drained.
Yes, ground cables can also be a culprit. I would start chasing those first with an older car (or a more "ordinary" one that is likely to have built up more corrosion), but with a car like this I usually start with the regulator as that is most likely to solve the problem. The brushes on the regulator really are a wear item and are guaranteed to cause the alternator to stop charging well eventually no matter how well the car was taken care of. The regulator is cheap and even if it wasn't the issue, it probably would become one in the near future.
My 996TT voltage regulator recently died. Before the car would always be just below or above 14V (say 13.8 to 14.1) and fluctuate with revs and load accordingly. My NA 996 has the same behavior.
When the regulator was on its way out, but before getting the generator light, I noticed during flat highway constant rev driving that I was sitting around 12V which was abnormal. Eventually it started varying with respect to ambient temperature (i.e. when outside temps were cold, I could see the voltage go higher).
Finally the check generator light came on and I wound up replacing the alternator. I checked my ground points and connections to the battery before jumping to that conclusion. With brand new alternator+regulator I'm back to sitting around 14V +/- 0.2V as expected. I originally purchased just the regulator, but after getting the alternator out and seeing some corrosion I decided to just replace the whole thing.
12.5V is probably a good indication of the widely documented voltage regulator being on its way out.
Also with fully replacing the alternator you won't have to worry about the fully going out as well. I know 40 bucks is cheap compared to a few hundred for a new unit but, the time saved and being all new takes all the worries out and cuts the labor time down.
06-20-2017, 12:00 PM
