602996TT

I have the same numbers as you posted it's been that way for 2.5 years since I put a new alternator in my car. I only really notice it dip close to 12.3 volts whens its over 110 degrees out here in Arizona with AC on low, radio, and headlights on at stop lights or traffic is most noticeable. A few Porsche mechanics I have talked to says it's completely normal on are cars?

Punko

From what i have read, it could be wiring is getting old and corroded....not sure.

I think Arizona climate is harder on batteries and alternators.

993GT

Hey Mark,
Check the engine to body ground, located near the passenger side turbo.

Rob

Kevinmacd

12.3 will not charge the battery.

neanicu

Anything above 12V with all of the accessories in the ON position is considered normal at IDLE. And notice I emphasize IDLE. You need to raise the RPM at that point and the voltage should go up. Then your alternator is fine.

Punko

So I jacked it up, removed the wheel and sanded the ground strap and fastener.

Measurements at battery.

Idle
14.02, was 13

Idle with everything on
13.35 was 12.3

rmc1148

993gt to the rescue= good info and glad it helped.

Kevinmacd

Punko there you go now you are on your way. Over 13.3 with everything on at idle is correct.

jpflip

WOW! In fact that is a very good call!!! I'm impress, congratulation 993GT!!!

993GT

glad it worked out!

neanicu

I'm not trying to argue,yet I was curios to find out whether your statement makes sense. So I went ahead and checked 3 cars : 997GTS,996TT and E46 M3. AC On full blast,heated seats On,High beam On,Rear defroster On. All 3 cars at IDLE showed little over 12V. So,you think all 3 cars have a ground problem? How was your ground : very corroded,loose?
I'm sorry,but I'm not buying it...

rmc1148

I use to buy and sell a lot of cars and cannot name the problems I solved by cleaning grounds and contacts on fuses etc. Vacuum lines being replaced usually fixed the other problems .

neanicu

I agree,although it is not the case here. I just hate misinformation.
Push me hard enough and I'll make a video.

993GT

when you say all those cars were at 'little over 12', can you be specific?
should all be ~12.5+, or the charging system/battery is undersized

neanicu

The E46 M3 showed 12.1V.
The 996TT showed 12.3V.
The 997GTS showed 12.5V,but no heated seats on this one.
My suspicion is that the OP didn't load up the system with so many accessories.
Again,put AC On full blast,heated seats-driver and passenger on high,Rear defroster(very important),high beam On and have the car at IDLE(again very important-we're not talking while driving here or a certain RPM-we're talking IDLE).