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So to start this off I just joined to ask my question after lurking about reading the forums for quite some time trying to resolve my issue. I have an 05 Cayenne, purchased it dirt cheap because of an "electrical drain". Long story short, the electrical drain was no drain, just a bad alternator. I replaced the alternator and figured I was good to go. While I was at it I replaced the battery with a brand new one. All was well until I drove it around for 10 minutes, and then turned it off. I came back out a few minutes later to show my wife that my "investment" was a good one. I turned it back on, start driving and then I get the Battery/Generator failure message on the dash. Now feeling defeated I installed a Bluetooth OBD reader so I could monitor the voltage while driving and let it sit overnight. Started up great the next day and is charging at 14.1v, no warning on the dash. Drove the car around for a while monitoring the voltage and it never changed. Get back home, turn it off, turn it back on and I am immediately at 11.8v not charging at all, but the voltage isn't decreasing either, I drove it around for about 10 minutes and still no decrease in voltage but definitely not charging, just maintaining. I drive back home, turn it off, wait about 30 minutes, go out start it and magically it's working great again, 14.1v, and no warnings. I only get the message after driving it for essentially any amount of time turning it off and then restarting again shortly thereafter. It almost seems like as soon as something is getting warm it needs to cool down before it starts actually charging again. I have tried everything I can think of trying to figure out what is causing the issue from turning the key waiting a moment and then starting, to turning off every accessory before starting but I have come up short. The other thing I have determined is that if I start it and the heater/AC fan motor doesn't turn on that it is going to give me the battery/generator warning. Does anyone at all have any ideas as to what the heck is going on and what I can try to figure it out? Thank you in advance!
 

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Is it possible that the OBD sensor is giving you a bad reading and in fact the system is working just fine? Try using a volt meter directly on the battery to confirm that you are in fact at 11.8v when the car is off and not charging and 14.1v when the car is running. Good luck.
 

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I believe that the OBD sensor is working as it should because when it reads 11.8v I get the dash warning and when it is reading 14.1v I am not. I would think that if the battery was draining while driving I should have different electrical systems shutting down as they lost the necessary voltage to operate. And the fan motor not working at all still seems really weird to me.
 

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I'm not making myself clear. I am not questioning the OBD's logic. I am questioning the circuit that is telling the OBD what the voltage is. Yes when the OBD senses that the battery is at 11.8 volts, it correctly turns on the dash warning light. But what if the battery is really not at 11.8 volts. You may ask why I would question that. Well 11.8 volts is extremely low for a 12 volt car battery. I just went down and measured my 2 year old battery in the car, not running, and it measures 12.05 volts. Anyway another thought; perhaps I did not understand but I thought you had put in a new battery as well as a new alternator. If you have not put in a new battery then that may in fact be your issue. You can take your car to say Autozone and they will test your battery for free. It may have a quirky cell or have been stressed by excessive discharge when the car had a bad alternator. ???
 

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Discussion Starter #5
Ahhh, I understand what your point is now. I did in fact put a new battery in when I put in the new alternator, but I have gotten a bad battery "new" battery before. I will go out and check the voltage with it not running and see what it says.
Thanks!
 

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OK, sorry for the delayed response, just been busy. This morning I checked the battery after it sat all night before I started it and it was reading 12.16v. I am still open to any and all ideas!

Thanks!
 

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Suggest you buy one of those cheap gizmos that plug into the cig lighter and light LEDs to indicate good or low voltage. If the problem is real could be a bad connection or bad wire. I wonder if it could be an underlying problem that also caused the alternator failure. What was wrong with it?


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Funny thing is that I started out with one of those cheapo LED things, and then went to the OBD thing so that I could see an actual voltage when it was running. I wish I knew the back story better, all I was told is that the battery kept dying and it to be jump started constantly. Once I got it home I put in a different battery, started it and saw that the alternator was most definitely not charging the battery at all. That's when I put in the new alternator and battery. The first time it happened I tore into every connection to the battery itself under the seat and cleaned absolutely everything that I could get my hands on. I was thinking that maybe the voltage was getting pulled down too low when cranking and that was causing the battery/generator warning. It didn't help at all... It has never been completely dead where I have had to jump start it, and it always starts right up which makes troubleshooting the problem even more difficult.
 

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So, I just uncovered some interesting information. Looking back into my paperwork the description for the alternator says 03-04 and mine is an 05. Technically it is still a 955 until 07 at which point it becomes 957 correct? Maybe that is the big problem? The fitment, cooling connections, and wiring connections were all the same so I'm hesitant to say that is the smoking gun. But maybe?? That's a pretty expensive pill to swallow if that indeed is my problem. Can anyone confirm or deny that there is indeed a difference between 04 and 05 on the alternator?
 

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Funny thing is that I started out with one of those cheapo LED things, and then went to the OBD thing so that I could see an actual voltage when it was running. I wish I knew the back story better, all I was told is that the battery kept dying and it to be jump started constantly. Once I got it home I put in a different battery, started it and saw that the alternator was most definitely not charging the battery at all. That's when I put in the new alternator and battery. The first time it happened I tore into every connection to the battery itself under the seat and cleaned absolutely everything that I could get my hands on. I was thinking that maybe the voltage was getting pulled down too low when cranking and that was causing the battery/generator warning. It didn't help at all... It has never been completely dead where I have had to jump start it, and it always starts right up which makes troubleshooting the problem even more difficult.
What do you see with the cheapo? Same as OBD or inconsistent? Good idea to check and clean! Would be cool if you could monitor the field winding voltage or current but I bet it’s tough. Not like my 914 with external regulator!


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Discussion Starter #11
The cheapo was pretty much the same as the OBD. With just a red, yellow, and green LED it never went off of the green light.
 

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The cheapo was pretty much the same as the OBD. With just a red, yellow, and green LED it never went off of the green light.
Hi kickercompkid, What was the outcome of your intermittent issue with the warning battery/genarator message?

I have a similar issue with my 04 CTT. I can drive 20 minutes fine. I stop at a store to pick up something, then I start the car and drive. Within minutes the "Warning Battery/Generator" light would come on. I leave it overnight. The next morning, the battery is at 12.3 volt. I start the car and the battery is at 14.3. No Warning light. I then drive it down the street. At the red light, the Warning Battery/Generator light comes on. I turned around and headed back home, the light went out. The battery is brand new. Could it be the alternator acting up or something else is wrong?
 
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