E38 Alternator Or Electrical Issues

[DPD327]

Hi Folks,

I have a 2001 BMW 740i with 7800 original miles (bought it new in 2001).

I am trying to trouble shoot an electrical problem that looks like it might be alternator related. After starting the car, for the first 3 or 4 minutes the voltage output is pretty normal up around 13.7 V but shortly after that, the voltage drops and the battery light begins to illuminate on the annunciator panel and sporadically lights up. No codes on OBC.

Battery is fine (in good condition but gets discharged once the voltage drop issues start).

Checked the ground wire, check the belt tension all good there....any ideas? Could it be a bad alternator or perhaps a control module?

DPD327

[Guest Mister Dabsy]

Battery is fine? Is it new or newish?... Reason I ask is BMW's get temperamental if the battery is not more than perfect !!

We'll go into other possibilities if the battery is spot on ;)

[DPD327]

Battery is good...tested it recently replaced about 2 years ago....keep the car on a battery charger in the garage.

[Guest Mister Dabsy]

You can get hold of a good alternator for 60 quid (or change the brushes for a tenner)...

But, first I would go over the connections and wiring methodically before spending...

I'm Still unsure of your battery

[DPD327]

Jack,

I am thinking alternator as well.....brushes sound like a good starting point and inexpensive as a first shot....but the fact that there is good voltage for the first three or four minutes of run time (after engine start) is leading me to believe something more integral to the alternator....possibly diodes or ??? The full replacement of the alternator might be a better idea and if I can find one on the cheap, that might be the way to go....your thoughts?

[Guest Mister Dabsy]

Exactly... No codes to go by so replace the alternator as their electrical diodes and what-have-you are in there too !

[DPD327]

Wish me luck!

[DPD327]

^Jack,

^{Replaced the alternator and that seems to have solved the problem.}

^:)

[Guest Mister Dabsy]

Happy days fella ;)

[jonpi]

Hi. I bought a 750i sorry new member.

I have a problem, sometimes the radio is working then it will go off, I will try and switch it on or off but nothing then it will come on itself also the spedo works fine then drops to 0 same with the washers sometimes they work then stop.

Navigation system has white screen which come on when starting the engine but won't turn on or off with the Button.

Any info would be appreciated

Jonpi

[Guest DazH]

Hi. I bought a 750i sorry new member.

I have a problem, sometimes the radio is working then it will go off, I will try and switch it on or off but nothing then it will come on itself also the spedo works fine then drops to 0 same with the washers sometimes they work then stop.

Navigation system has white screen which come on when starting the engine but won't turn on or off with the Button.

Any info would be appreciated

Jonpi

Hi, Welcome

Please make a new thread regarding your issue for maximum exposure. Follow the link and make it in there:

http://www.bmwownersclub.com/forums/forum/10-bmw-7-series-club/

Daz

[Niki]

Hi I have had new alternator on e38 735i but despite auto electrician saying it's fine no codes it isn't fine cause I have to charge it every night like I'm up on the !Removed! milk float revolution. What the hell garage no good they didn't try much cause the former are legends but I'm not feeling so confident about them now. It's getting to me now.

[Greydog]

Hi Niki

Not trying to "teach Granny" but assuming the Battery has been checked and is in good condition and also assuming  the alternator fitted was the correct one for the car, you could have a parasitic drain killing the battery overnight. I would fully charge the battery either by a good run or with a charger disconnect the battery from the car leave it 12 hours and check it if it is still fully charged. If it holds a charge off the car then the issue is with one of the systems on the car 

Dave