weird electrical problem

[E90_M3_Dubai]

hello everyone ,

First ...Please excuse my bad english

I need your help

So I have a 2008 Manual E90 M3 with a lil over 70K miles on it and I just had the battery replaced (first time since purchased ) which died suddenly with no prior symptoms of it dying or running low or anything .
But I went ahead and got an aftermarket battery (not OEM BMW battery ) and replaced it and it was fine ..or I thought so

after the battery incident a became obsessed with monitoring the battery voltage , and i have a P3 vent gauge so I set it to batt and observed the voltage all the time , so Ive noticed that when the engine is not on the voltage is always 12.1v~12.7v which is normal (to my understanding) but when I turn the engine on it does the following : ( This is the weird part )

80% of the times I turn on the car the voltage will remain 12.6 and start to drop all the way to 11.4v for as long as i'm driving the car ( I checked it for up to 2 hours drive )

20% of the time I turn on the engine and the voltage quickly go up to 14.6v then keep steady for like 5 minutes then drop to not less than 13.5v and fluctuate between 13.5v and 13.8 and sometimes up to 14.1v and it stays between those numbers till I turn it off !!

so if I start the engine and noticed the voltage is 12.somthing I would turn it off and on multiple times till I see the 14.5 voltage and then drive , out of fear that if I kept driving it on the 12.v it will eventually drain out and die on me .

now in all those times I never had a CEL or an error code of any kind , the only time I got a code is when the battery died on me the first time and then I saw the battery discharge increased error for the first time and it never came back after I replaced the battery .

So If i didn't have the vent gauge I would've never noticed because no errors were there on the dash also there is no hesitation or engine stalling ..this is just from my observations at the vent gauge .
But i'm positive that 11.4v while engine running IS NOT NORMAL and I want to know if any had those symptoms before or somthing close to it ..is it my alternator switching off and on ? because even idle is higher when voltage is higher ..so when I turn the engine and it finally on 14v my idle would be around 900 while its around 780 rpms when I turn the engine and its on 12.3v or less .

i'm completely confused , dunno if its the battery or the alternator or the IBS or..or..or !!

More over , i'm on BPM stage 2 tune with cold start removed and I DID NOT register the new battery .. Yes i didn't but don't tell me that this will cause my alternator to shut down for one cycle and work on another ! because it doesn't make any sense ..


so yeah ..this is pretty much it ...HELP ME PLZ

[Petros]

it might be because you didn't register the battery. These cars are designed according to German philosophy, which state something like "why design one simple part to do the job when 10 more complex less reliable parts can do the job just as good?". While most other cars use a simple voltage regulator to control alternator output, this car uses an "intelligent" system that monitors the battery condition and calculates how much voltage it needs to be fully charged again.

If you put a new battery without registering it, the computer doesn't know the battery was changed so it will keep using the efficiency data from monitoring the old battery to determine how to charge the new battery. Since the new battery will likely not behave in the same way it is possible this confuses the car's computer and causes this erratic voltage output.

Also did you use a battery with the exact same specs as the OEM one? If it is a different type or has a different capacity then you may need to code the car for the new specs, and not just register the new battery. If it's the same spec as OEM then just charge the battery fully on a trickle charger and register it immediately after that.

[E90_M3_Dubai]

@petros Thanks for the reply ..

I was debating this actually and I get what you are saying ... the new battery is not the same specs as OEM as well .. The dealer here wont register or code anything if its not bought from them ..if you guys thought your dealerships are Stealerships you have to see them in dubai ! those guys are like Mafia over here !! for a new battery and installation ( with registering ) they have quoted me for AED6800 which is almost $2000 ! for a battery !

Anyways , sorry for the rant .. Can someone provide me guidance on how to do it my self ? I know its possible but is there a simple DIY for that ? I tried searching but couldn't find a clear cut for the M3 , everything I found was for non M cars .

Also any different opinions there ? maybe its not the battery registration ?

[Petros]

registering is easy. You buy a K+DCan cable and download BMWLogger free on a laptop. But if your battery is different from OEM you might need coding which is a bit more inovlved. Not sure how it's done. Maybe you can message mike benvo who is on this forum. He might be able to do it for you online

[E90_M3_Dubai]

hey , just to update you guys .. it turned out to be the alternator voltage regulator ,after I changed it everything ran perfect !

[mannuelr1]

Hi.
I am currently having this same problem on my e93 M3
I even did the same experiment with a voltmeter all day connected
Same results.
Weird never got a code for the problem.

So, i expect to get it fix by just changing the alternator voltage regulator.

I wonder how do you find out it was the voltage regulator?

And, did you have to buy the complete alternator or were able to get only the regulator?

I have been looking for day for some information on this issue.
I am glad you wrote this post and were so datailed on the explanation.

[kenwelch]

Originally Posted by mannuelr1

Hi.
I am currently having this same problem on my e93 M3
I even did the same experiment with a voltmeter all day connected
Same results.
Weird never got a code for the problem.

So, i expect to get it fix by just changing the alternator voltage regulator.

I wonder how do you find out it was the voltage regulator?

And, did you have to buy the complete alternator or were able to get only the regulator?

I have been looking for day for some information on this issue.
I am glad you wrote this post and were so datailed on the explanation.

The regulator is available as an individual part.
http://parts.bmwofsouthatlanta.com/p...317847517.html

[E90_M3_Dubai]

I was lucky I have the P3 vent gauge and I had it set on Voltage so I was monitoring the voltage and I notice how it drop and how it picks up randomly ...then generally speaking alternators are not that complicated so if the mechanical part is squeaking and making noise it means you have to replace it but if it didn't then you don't have to ... and so I knew the problem would be that chip in the back of the alternator ( voltage regulator ) ..and it was !

good luck on the e93

[IMG]

I replaced my battery and didn't have to register anything and car runs fine !

Glad to hear OP got it sorted out !