Sorry for the long post but here it goes: i have a 2007 base model 6 speed. I was driving one time and the red battery light came on, then off, then on, until the car spazzed out and died. Autozone tested and said the alternator was junk. So, i replaced it myself, drove it around 6 hours with absolutely no problem. However, 2 days ago, the red light came on and off until it died again. my dad and grandpa hooked up a different battery and that battery died as well but without the red battery light warning! everything lit up at once as it died. While trying to jump start it it wouldn’t even turn over. the yellow battery light stayed on. So, we thought it was a bad alternator again but a shop said it could be the ECU. I went out today, reconnected the battery (a little spark happened), and i was able to put up my windows unlike before! somehow the battery regained power disconnected? Does anyone know what the problem could be? i’m in college with not much money and i’m stumped.

 

Sounds to me like the "new alternator" is bad....take it off, have it tested by a couple places.....also, put a battery charger on your car battery before starting the car......alternators are made to keep the battery at full charge, they are not designed to charge a dead battery

Where did you get the alternator from??

Bryan

 

 

Have the Autozone guy test the new alternator anyway, they can be bad out of the box.
Who does he think he is? He's a clerk, not a mechanic.

 

The kid behind the counter at the parts store will say anything to not warranty the alternator......and how does he know the ECU is bad? How does he know the regulator is inside the ECU?

I actually don't think the regulator is inside the ECU, I have 2 MINI's....an '04 & an '06.....if I remember, both my cars have the regulator inside the alternator.....

I hate to say it, but the parts store clerk is an idiot.......take the alternator off and have it tested, take it to a few places....don't rely on the test done at Autozone.....

Bryan

 

Ask the guy at Autozone exactly how the DME controls the alternator output. Then ask him what keeps the battery voltage at 13-14 volts when the engine is running at varying RPM ... that would be the voltage regulator. For some real fun, ask him if the alternator output is AC or DC, and then ask him how a full wave rectifier circuit works. Finally, ask him for his ASE certification card. When you want to know how things work, read your Bentley service manual or ask a tech at your local indy shop ... not Autozone.

From http://www.madelectrical.com/electri...witworks.shtml

[SIZE=2]THE METHOD USED TO ADJUST ALTERNATOR OUTPUT [/SIZE][SIZE=2]The voltage regulator adjusts alternator output by controlling the amount of power it will send to the magnetic field winding in the alternator. (Alternators work through the use of magnets.) More power delivered to the magnetic field winding in the alternator will produce a stronger magnetic field, which causes the alternator to produce more power output. Alternator output is reduced when the voltage regulator delivers less power to the magnetic field winding in the alternator, as the strength of the magnetic field will be reduced. [/SIZE]

 

I called various mini dealerships and they all said the alternator voltage is controlled by the ECU, not a voltage regulator, but after describing my problem to them, they're thinking something might be drawing power from the battery while driving, more than what the alternator is charging. I'm truly stumped by this problem. I went out again today, reconnected the battery and it had some juice again! However, after trying to start, all the lights went out and it didn't start and nothing happened after that. I need to charge the battery soon.

 

lol point proven. The mini dealership said that the voltage is regulated by the ECU, not a voltage regulator, so it couldn't be the voltage regulator going bad. Could be a bad connection somewhere? As soon as I try to start the mini, all the lights go out and the battery goes stone dead. I'm just confused as to how every time I reconnect the battery, it has somehow regained a little bit of juice which has enabled me to close the windows, use the FOB, etc. I might get a replacement alternator just to be safe but I don't know

 

That's a fair point. I had it tested and the alternator was only putting out 11.9 instead of 13 minimum, but since the battery was low they said it could be inaccurate

 

Well, this is from the newtis.info website; item 2 in the picture below is your regulator (it's inside the alternator); the rectifier diodes change the AC voltage produced by the alternator to DC voltage through a full-wave rectifier circuit (It's the magic inside.). Notice in BMW's own functional description "The alternator maintains the desired level of vehicle voltage." Based on what you are being told by the dealer, it should say "The DME maintains the desired level of vehicle voltage." Either BMW's authors or the dealer mechanics have it wrong. I'll stick with the BMW authors.

Feel free to read it for yourself and share with your local dealer service department.

https://www.newtis.info/tisv2/a/en/r56-cooper-hat/wiring-functional-info/power-train/engine-electronics-mev/voltage-supply/alternator/XXfFDg8



Cheers!

 

Never buy an alternator from Autozone, I've done it 3 times on a MINI and they were all bad, one of them kept shredding the drive belt off. I find O'Reilley's alternators to be an exact fit most times.