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Discussion Starter #1
Started having my new-to-me 2008 M5 show the 'High Discharge' and other associated electrical quirks from not enough electrical power. A couple days ago, the car wouldn't start from a low battery so I pulled the battery (the car was stranded away from my house) and charged it overnight on a digital charger. The battery was holding 12.4 volts so I put it back in and drove it to the local dealership who promptly informed me my alternator was bad and it would be $1,600 for the new alternator (everything included). The car just turned 40K on the odometer so I'm very surprised it's the alternator. After reading a bunch of posts, I'm leaning towards the regulator being bad and I need to convince the dealer to just install the regulator instead of a whole new alternator.

So my question is: What are the odds the regulator is bad and is only putting out 10.4 volts? I know with high voltage, it's almost guaranteed to be the regulator.

Anything else I should check before even thinking about a new alternator???
 

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DinanS2+ e60m5 6MT, s38b38 e28m5 TT/ST3, e30 TT/ST4
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Sounds like it could be your regulator. I went through the same exercise, but at 70,000 miles. At 70,000 miles, I just replaced the entire unit.
 

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If it's putting out any voltage at all, it's more than likely the regulator i'd say.
 

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Carbon brushes locate in the regulator, and it very well could be that these brushes are worn. I believe even only the carbon brushes can be replaced, but you would need to find the right size ones. I'm not sure if there's any info easily available on this. The brushes only would be something like 1-3 euros/US dollars.

- Antti -
 

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See if you can find a good indy service place. I picked up my 08 w/ 41k miles about a month ago, and had similar problems. IMHO it's just the regulator, and from what I understand that can be replaced with a bit less labor.

I had a 60 day warranty, so I got them to swap out both alternator and regulator. If I was paying the bill, I'd have just done the regulator first. Mine also stranded me twice while I was sorting it out... loads of fun there.
 

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Discussion Starter #8
I have a good indy in Austin and I'll get the car over to him in the next day or so to install just the regulator. The only reason I had it taken to the dealership was the battery is only a year old and still under warranty. When I pulled the battery to get it charged, I also had it tested at the local Sears which was next door to where the car die. Sears charged the battery and said it was bad so I was hoping it was just the battery...maybe not.

Either way, I'm not too happy about the course BMW has taken with their 'new' cars. With all the electronics on these cars, they really need an electrical module/computer battery and a cranking battery. Sounds like Mercedes is already doing that... I've been stranded a couple times in my E39 M5 when the battery started to weaken and the voltage would drop below 10.5v or so. The computer wouldn't let the car crank even though the battery was capable of doing it. So, you go from the car starting normally to the car not even cranking when the voltage just dipped below some threshold. It's not like in the old days when you could hear the starter bogging down from a weak battery...oh and you had a volt/charging guage and a battery light that would turn on if the alternator stopped working. With all the fancy electronics, you would think there would a nice message about bad battery or weak alternator... Nope- never had one appear in my E60. I know I"m ranting now but seriously, the car can 'learn' my driving habits and adapt steering, throttle, SMG, etc. responses but it can't tell me when the alternator is weak??? Sad...
 

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DinanS2+ e60m5 6MT, s38b38 e28m5 TT/ST3, e30 TT/ST4
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I have a good indy in Austin and I'll get the car over to him in the next day or so to install just the regulator. The only reason I had it taken to the dealership was the battery is only a year old and still under warranty. When I pulled the battery to get it charged, I also had it tested at the local Sears which was next door to where the car die. Sears charged the battery and said it was bad so I was hoping it was just the battery...maybe not.

Either way, I'm not too happy about the course BMW has taken with their 'new' cars. With all the electronics on these cars, they really need an electrical module/computer battery and a cranking battery. Sounds like Mercedes is already doing that... I've been stranded a couple times in my E39 M5 when the battery started to weaken and the voltage would drop below 10.5v or so. The computer wouldn't let the car crank even though the battery was capable of doing it. So, you go from the car starting normally to the car not even cranking when the voltage just dipped below some threshold. It's not like in the old days when you could hear the starter bogging down from a weak battery...oh and you had a volt/charging guage and a battery light that would turn on if the alternator stopped working. With all the fancy electronics, you would think there would a nice message about bad battery or weak alternator... Nope- never had one appear in my E60. I know I"m ranting now but seriously, the car can 'learn' my driving habits and adapt steering, throttle, SMG, etc. responses but it can't tell me when the alternator is weak??? Sad...
Regarding your e39...why couldn't you just pop the clutch? Worked on my e39, when my battery was flat -- another reason my e60 has three pedals. :tonquesmilie:

Kidding aside, I hope it's just your regulator. Please keep us posted on the outcome.
 

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If an alternator has made you so sad, I cannot even imagine what the rest if the car would do to you.

Anyway, your first post says that the car was showing a "high battery discharge" warning for a few days. So it did give you a warning. It was you who decided to ignore it and not do anything about it.



Either way, I'm not too happy about the course BMW has taken with their 'new' cars. With all the electronics on these cars, they really need an electrical module/computer battery and a cranking battery. Sounds like Mercedes is already doing that... I've been stranded a couple times in my E39 M5 when the battery started to weaken and the voltage would drop below 10.5v or so. The computer wouldn't let the car crank even though the battery was capable of doing it. So, you go from the car starting normally to the car not even cranking when the voltage just dipped below some threshold. It's not like in the old days when you could hear the starter bogging down from a weak battery...oh and you had a volt/charging guage and a battery light that would turn on if the alternator stopped working. With all the fancy electronics, you would think there would a nice message about bad battery or weak alternator... Nope- never had one appear in my E60. I know I"m ranting now but seriously, the car can 'learn' my driving habits and adapt steering, throttle, SMG, etc. responses but it can't tell me when the alternator is weak??? Sad...
 

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Discussion Starter #11
your first post says that the car was showing a "high battery discharge" warning for a few days. So it did give you a warning. It was you who decided to ignore it and not do anything about it.
I disagree. High Battery Discharge is not the same issue as Alternator Not Charging. Granted, after reading the board and seeing "high battery discharge" is to be interpreted as a faulty alternator, sure, the Beast did tell me something was wrong. But only after researching the board is this known.

Anyway, as a follow up to close out the post, I replaced the regulator ($65 for the piece, $9 for shipping, and $250 for labor at the local indy) and the car is working great now. Saved over $1300, thanks to the guys on this board. Much appreciated.
 

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This kind of sh*t is why the cars are worth <30k

You can get a new alt with voltage regulator here, oem for an ok price. I am sure you can find any non dealer shop to install it for under 400 bucks.
2008 BMW M5 Alternator 5.0L Engine - 170 Amp - With Valeo Unit 31-01451 AN

1600 no way! Prices like that are crazy. Get it all done for 700 something bucks and keep the extra 800 + for something else.
BUT its why i can buy one cash! Any time bmw crows about resale value i laugh...
 

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If you are electrically savvy at all, crack the old regulator open and figure out what is wrong with it. Or ship it to me. I will figure it out.
 
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