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E90/E91/E92/E93 (2006 - 2013)
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  #1  
Old 09-11-2013, 05:45 PM
cokewithvanilla cokewithvanilla is offline
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Mein Auto: 2007 BMW 328i
E90 2007 Voltage dips

Hello

I have a 2007 e90 with some voltage issues. The voltage when off is 12.4. When running at normal speeds it's between 13.7-13.9. When I am driving at low speeds in stop and go traffic (mainly when braking hard), the voltage often dips to 12.4. Around 15mph, 500-700rpm, the voltage will dip to 12.4 and the AC will slow down then speed back up.

I replaced the battery 6 months ago. I do not think the battery is the issue as it has proper voltage when off. Is this a voltage regular/alternator thing?


One more note... recently I did a hard stop from 80 to 0. The car shut off.
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  #2  
Old 09-11-2013, 07:20 PM
jburke4689 jburke4689 is offline
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I think the shutting off is unrelated to your issue. Here is what the service manual says.

Ignition off at battery should be 12.6v
Engine running should be between 13.5 and 14.5v
Run engine at 2,000 rpm. Turn on fan, rear window defog, wiper and lights, etc. With all accessories on voltage should be 12.6,
Engine running, battery charged accessories off is usually between 13.2 and 14.5
If it is over 14.8v you have a faulty voltage regulator.

I think your alternator is fine based on your post.
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Old 09-11-2013, 07:26 PM
cokewithvanilla cokewithvanilla is offline
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Ok. Is the fan supposed to drastically change speeds based on engine rpm? The voltage dips at low rpm to the point where the ac slows enough that you really notice. This doesn't seem to be normal operation.
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Old 09-11-2013, 08:04 PM
jburke4689 jburke4689 is offline
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It is. The power management system can reduce or shut down electrical loads when the alternator can't keep up. This could happen at idle with the blower on. It uses as fair amount of power.

If the battery charge status is critical and the alternator is at maximum input then the blower motor is reduced to 75% then 50% then 25%. So that being said, your battery shouldn't be critical unless it is old.
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Old 09-11-2013, 08:58 PM
cokewithvanilla cokewithvanilla is offline
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So it slows down, then speeds up immediately. It doesnt even register the change on th climate control. If the battery were bad, this would make sense, right? But the battery isn't.

:/
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Old 09-11-2013, 09:14 PM
fdriller9 fdriller9 is offline
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Did you have the battery cable recall done?

Also how are you monitoring voltage while driving?
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Old 09-11-2013, 10:08 PM
cokewithvanilla cokewithvanilla is offline
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I have not. Would this be covered at 114k?

Using test 9 on the dash
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Old 09-12-2013, 09:09 PM
fdriller9 fdriller9 is offline
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Quote:
Originally Posted by cokewithvanilla View Post
I have not. Would this be covered at 114k?

Using test 9 on the dash
Yes, if your car's VIN falls under the recall.
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