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2001 530 Electrical (Alternator?) Probem

Discussion in 'E39 (1997-2003)' started by michaelkimball, Jul 27, 2013.

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    michaelkimball

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    I had an interesting thing happen on the way home yesterday in my 2001 E39 (170K miles). As I went around a corner rather sharply all of the warning lights on the dash went on (including the battery light and the transmission warning light) and the car went into "limp home".

    The car has a new (~3 months old) battery and is kept on a trickle charger as I don't drive it much, and when the battery was replaced, the alternator checked out fine. I checked the battery and it is not loose, nor are the battery cables.

    At 170K miles, I can certainly understand needing to replace the alternator, but having it happen exactly as I turned hard, makes me wonder if there isn't something else going on. (I've been around tech too long to believe in coincidences).

    Anyone have any suggestions? Unfortunately, the nearest BMW trained technician is about a 90 minute drive away....
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    charlson89

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    I would suggest you take a volt meter that has a feature called MIN/MAX use that setting and hook it up to the battery positive and negative terminals and then go drive and make the lights come on then check your MIN and Max values if your battery voltage is lower than 13v then you know the alternator is not charging properly.
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    michaelkimball

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    I know the alternator isn't charging correctly. I just think the warning lights coming on as I cornered hard is a very unusual "coincidence".

    I'm hoping someone has some insights into the cause of the failure so I don't just end up replacing parts.
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    charlson89

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    If voltage in the vehicle isn't correct in the vehicles electrical system the computers of the vehicle will go into protection mode and shut down. So in your transmission the module shuts down and the vehicle goes into limp home mode. But of course you will need to check your transmission fluid level to.
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    michaelkimball

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    I understand why the car went into limp home mode and the secondary effects from the low voltage.

    What I'm trying to figure out is why the voltage is low. At the simplest level the reason is the charging system isn't charging the battery; but I'd like to know why before I take it to a mechanic and they start replacing the parts. It just seems really odd that the fault would occur in the middle of a hard corner.

    If the corner were related to the fault, it would seem something is loose. Since I've already checked the battery and cables, I can't think of anything else that is likely. If the alternator bearings were bad enough to cause a problem or the alternator itself were loose, it would either fail rather spectacularly or it would make noise.

    OTOH, there there isn't much to a charging system and the voltage regulators are integral to the alternator, so maybe replacing parts isn't such a bad idea; I just like to know what the fault is.

    Having had some rather interesting experiences in a former life, I've found paying attention to all the indicators helps a lot.
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    CRKrieger

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    Although the voltage regulator is 'integral' to the alternator, it's a separate part, easily replaceable - and a lot cheaper than an alternator.

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