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Discussion Starter #21 (Edited)
But whenever it failed the battery light on dash should turn ON; OP didn't say ever seen the battery light.

Alternator is easily tested: let engine idling, turn on headlights and if no battery light then it is still good.
Yea, battery lights doesnt come up and never did

I think light should come up when ur alternator is just dead, 0 charge to battery
I mean alternator can work but badly. so it doesnt show battery light?
 

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2018 Audi S4
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I'd do the voltage regulator and see what happens with the voltage levels. My car shows 14.1v a minute or so after startup on OBD Fusion and <12.5v before starting. Never fails me in even the coldest weather. All this talk about needing high voltages to start these cars confuses me. My work truck has a 12L Cat and the alternator runs between 13.1-17v and keeps 3 batteries charged without engine speeds above 2100 rpms.

When I had alternator issues on my xi the battery light never came on either, the last time the battery voltage was down to 10+v.
 

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But whenever it failed the battery light on dash should turn ON; OP didn't say ever seen the battery light.

Alternator is easily tested: let engine idling, turn on headlights and if no battery light then it is still good.
My light never turned on when I had the same issue :dunno:
 

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Maybe irrelevant, but...
Have you had any issues with your Climate Control, as in random speed fluctuations, lack of ability to get full speed, or anything else that just seems weird? When the FRU goes bad one of its manifestations is a random battery drain. Sometimes it’s fine, sometimes it leaks a little, some mornings your battery is stone dead. I have replaced several over the years and it’s manifestations of failure are never exactly the same each time. It has happened often enough I keep a spare on hand.
 

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Discussion Starter #25
Maybe irrelevant, but...
Have you had any issues with your Climate Control, as in random speed fluctuations, lack of ability to get full speed, or anything else that just seems weird? When the FRU goes bad one of its manifestations is a random battery drain. Sometimes it’s fine, sometimes it leaks a little, some mornings your battery is stone dead. I have replaced several over the years and it’s manifestations of failure are never exactly the same each time. It has happened often enough I keep a spare on hand.
Naah, not really. Everything is fine except my A/C dont work but that not a big deal for me
 

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Discussion Starter #26 (Edited)
Changed brushes today. So old brushes were very short which needed replacment 100%. Seems like they were never changed
My dad had plenty of brushes collected for years. Choosed which will fit better and solderen in.
1st. startup not much difference, but voltage seems little bit higher and stable.
2nd startup everything was great, dash test showed 14.2 without load. With load something like 14, dont remember exactly, but it was good
3rd startup again in old boat. While driving with lights, music, climate control on low speed, dash test shows 13.0-13.1 volts everytime. Heavy load: music, max fan speed, interior lights, highbeams with lowbeams and blinkers, drops to 12.7v
Gonna check brushes again tomorrow. What could happen? Everything seemed ok and then suddenly again, maybe even worse?
 

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Discussion Starter #30 (Edited)
Reporting in again. Found problem with lot of experiments.
My positive cable right at trunk causing all those low voltage problems.
When I lift up positive terminal cable it jumps to 14v. Also cable heats little bit right at that metal thing (black arrow in photo)
Where white arrow is, cable seems crooked and swollen, basically damaged.
What fixes u guys can suggest besides spending 500$ on repair kit for cable?
Image for understanding, not my photo tho and ignore red arrows!https://prnt.sc/qaul3r
 

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2001 325i MT, 2001325i ZF auto,1999 328is auto
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When the regulator brushes wear past the halfway point, its time for a change!
This can cause drain and low output due to brush spring limit.
 
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