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2002 BMW 325 Alternator Charging, possible ECU

Tiny
CABOSS302
  • MEMBER
  • 2002 BMW 325
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 80,298 MILES
I have 2002 325Ci that will not charge properly. The alternator was bench tested at !13.2volts. On the the car it will generate more than 0.25volts. Using a digital multi-meter, the green wire with brown stripe (key on) produces the same voltage as the battery. The blue wire has ~ 1 volt less. Oh, when reving the car past 3Krpm, the generator will produce 1 volt and no more than 1 volt.

I'm presuming the blue wire is the exciter wire but am not sure. If this is the case, would the 1 volt drop be sufficient to prevent charging? And, what is causing the voltage drop?

Any ideas would be really appreciated as I've tried everything.
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Monday, July 28th, 2008 AT 2:39 PM

4 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Test the battery open voltage should read 12.4volts or better. Now start the car the voltage should increase 2volts over the open voltage if not recheck the alternator
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Monday, July 28th, 2008 AT 2:58 PM
Tiny
CABOSS302
  • MEMBER
  • 2 POSTS
The open voltage is 12.87 volts. The alternator has been tested at least twice and replaced with a new one. Just to make sure. Still no luck.
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Monday, July 28th, 2008 AT 5:06 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check all fuses and track wire for an open/short circuit-


https://www.2carpros.com/forum/automotive_pictures/12900_alty1_9.jpg




https://www.2carpros.com/forum/automotive_pictures/12900_alty2_3.jpg

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+2
Monday, July 28th, 2008 AT 5:50 PM
Tiny
DOCHAGERTY
  • MECHANIC
  • 9,601 POSTS
The alternator in the E-46 uses Bit Serial Data from the Digital Motor Electronics to excite the alternator. If the alternator has been replaced then the next item is looking at the wave form at the DME for output.
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Monday, July 28th, 2008 AT 8:17 PM

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