Red Battery Light HELP!

[tayyib330i]

Hey crew,

So today after leaving my friends place the red battery light turned on, so I drove home to get my car to a safe place. I did the voltage test and it was reading 99, and when I started the car the voltage shot down and went back up to a steady 94/95. When I was driving home the speakers were working and when I got home they weren't. Given this do you think it's my alternator that went out or the voltage regulator (I also read that people say something about the "brushes" failing). The car is starting fine, but i have a feeling the battery will die soon enough (because it starts rough). If anyone has gone through this can you please run me through the process you went through to diagnose the problem, any help would be great. I don't leave near a dealership, so I can't go to them. (I spent hours replacing my sunroof cassette today, and the day I finally have a working sunroof, this bs happens.. Whatta way to end the night :/ )

Thank you in advance

[Newjack]

Hey crew,

So today after leaving my friends place the red battery light turned on, so I drove home to get my car to a safe place. I did the voltage test and it was reading 99, and when I started the car the voltage shot down and went back up to a steady 94/95. When I was driving home the speakers were working and when I got home they weren't. Given this do you think it's my alternator that went out or the voltage regulator (I also read that people say something about the "brushes" failing). The car is starting fine, but i have a feeling the battery will die soon enough (because it starts rough). If anyone has gone through this can you please run me through the process you went through to diagnose the problem, any help would be great. I don't leave near a dealership, so I can't go to them. (I spent hours replacing my sunroof cassette today, and the day I finally have a working sunroof, this bs happens.. Whatta way to end the night :/ )

Thank you in advance

It sounds like either your voltage regulator is failing or your alternator is failing.

What year is the car and how many miles? How many times have you started it since the light came on and how long did you drive it with the light on?

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[LivesNearCostco]

What are 94 and 99? Can you give the voltage readings with the car off and the car running? It does sound like a failing alternator, or at least a loose connection to the alternator or one of the engine ground cables. If the voltage reading is same or lower with engine running as it is with engine off, then it's probably the alternator. When an alternator fails, it's usually the voltage regulator, but it's not always easy to buy just the voltage regulator (depends which alternator you have, there are 3 or 4 Valeo and Bosch variants for the E46).

[tayyib330i]

Thanks for the quick responses!
But Newjack it is a 2003 and with 123000 miles (she's getting old haha) and literally drove maybe 2 to 3 miles. And I started it 4 times just to do the voltage test. I did hit a bump goin at a decent speed prior getting to my friends place (didn't see it ahead of me) so possibly it's a loose connection.

And Livesnearcostco, that's what the voltage test was showing on the screen, from what I read those number just become 9.4 & 9.9 volts (correct me if I'm wrong). And about the different variants of alternators I read that online too, I'm goin to look at which one I have. And while I do that I'll look for the connections and see if they are loose or not.

Thanks again!! Greatly appreciated :D

[Newjack]

Thanks for the quick responses!
But Newjack it is a 2003 and with 123000 miles (she's getting old haha) and literally drove maybe 2 to 3 miles. And I started it 4 times just to do the voltage test. I did hit a bump goin at a decent speed prior getting to my friends place (didn't see it ahead of me) so possibly it's a loose connection.

And Livesnearcostco, that's what the voltage test was showing on the screen, from what I read those number just become 9.4 & 9.9 volts (correct me if I'm wrong). And about the different variants of alternators I read that online too, I'm goin to look at which one I have. And while I do that I'll look for the connections and see if they are loose or not.

Thanks again!! Greatly appreciated :D

Regardless of the car running or not that voltage is really low. How old is the battery? Signs still point to the alternator, but when my battery finally quit on me, one of the cells died. I couldn't start my car, however I did have power on the dash. My voltage reading was really low just like yours.

You could try swapping a battery, but my guess with that mileage is that your alternator went.

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[brettbimmer]

Alternator or voltage regulator. Battery is low because it's not getting charged with the engine running. Be really, REALLY careful that you get the regulator with the correct plug. Ask member Johnmadd about this!

Sent from my pineapple under the sea.

[brettbimmer]

Also, battery may need to be charged to be able to start the car with the new regulator/Alternator if the battery is reading anything near 12 volts with the car off.

Sent from my pineapple under the sea.

[BCS_ZHP]

If you have an OEM BMW battery, stamped on top of the negative post will be 4 numbers which signify the week of the year and the last 2 digits of the year in which your battery was produced. If it's a BMW battery past 5 years old, replace it. On a 2003 & if it's an OEM battery, I'm suspecting you're at the useful end of that battery's life.

BTW, the one alternator I've had go bad emitted an electrical fire smell, it was easy to diagnose it as the failure point.

[tayyib330i]

Okk thanks for the replies and sorry I've been traveling the past week so haven't got time to reply. My battery is almost 3 years old, so I took it in and they replaced it(warranty was done in 2 months, lucky me). I then start it and the red battery light is still on. I'm just gunna take the car to a local mechanic shop (that I trust haha) and get them to check if the alternator is done or not. I'll keep you guys posted!