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      04-02-2012, 01:24 PM   #13
Pheonix
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Drives: 2007 Z4 M Coupe 2012 e93 M3
Join Date: Sep 2008
Location: Bay Area, CA

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2007 BMW/Z4MC  [0.00]
A quick google search given these steps to quickly diagnos the charging system.
When your charging system is having issues test it with these steps to isolate the problem.

"Check the battery. Ensure that the connections are very sound and that the clamps and terminals are clean to insure a good connection.
With the engine running and headlights and accessories off, measure the voltage across the battery terminals. If the charging system is performing properly, the voltage should be between 13.3 volts (DC) and 14.7 volts. If you measure this voltage within this range the charging system is should be working properly.
A shorted diode in the alternator can still allow a charging voltage of up to 13.3 volts, and can be detected by the battery going dead within several hours.* If this happens, charge the battery out of the car to confirm it is still good.* If you are still experiencing charging system issues, then the battery is suspect.
If the voltage measured in step one is outside the range, check the voltage across the alternator output terminals. On the alternator, the top large terminal is the positive and the lower large terminal is negative.* The voltage across these terminals should be between 0 and 0.4 volts higher than the voltage across the battery."
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