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Discussion Starter #1
Hi all,

I've was driving along the motorway to work and my car cut out. It started with the radio turning on and off, then the battery symbol came on. The speed dropped down to 0 but the rev counter stays where it was. When I pulled over the car wouldn't start again but when the road side recovery got to me they jump started it and every thing was back to normal, showing a fully charged battery!

Anyone got any idea what I would start looking for the cause of this problem? I have no idea!!!

Thanks
Tim
 

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Discussion Starter #4
Sometimes it's the connection to the battery. Factory recall for the e90 so check with dealer

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Oh, ok. Hope it's that. Would they be able to tell if I phone them up and give them the VIN number or would they have to have a look at the car?

Thanks for the reply.

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Or your alternator is failing. Start the car and disconnect the negative battery cable while it's running. If the car dies your alternator isn't doing it's job.
 

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Voltage regulator.
 

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3/2007 328xi E91
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Or your alternator is failing. Start the car and disconnect the negative battery cable while it's running. If the car dies your alternator isn't doing it's job.
I would strongly suggest NOBODY try that. :tsk:

Most cars I have owned since EFI computers came into use have a warning at the battery area (at least those with battery in trunk) saying NOT to disconnect battery with engine running. My understanding is that the battery serves as a "buffer" to stabilize system voltage, and that disconnecting while alternator is operating can cause voltage spikes which can damage electronic modules. Here is what Bentley says regarding E9x systems (p. 121-3):
• Do not disconnect battery, alternator or starter wires while the engine is running.​

If you want to know if the alternator and voltage regulator are working properly, simply measure voltage at the Jumpstart Terminals under the hood with the engine running. Voltage should be in the range of 13.5V to 14.8V. If you get readings either above or below that range, your alternator, voltage regulator, or associated wiring may have issues.

You can also use Hidden Menu 9.00 to read System Voltage on your instrument cluster as you drive, and should use that tool if you have any reason to wonder about alternator output:
http://e90.wikifoundry.com/page/BC+hidden+menus

George
 

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You're right, my bad. I didn't take into consideration what year his car is. Im too used to working on older ones. I apologize, hope no one tried that. Just use a multimeter instead.
 
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