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Old 09-12-2019, 08:40 AM
doane2u doane2u is offline
doane2u
Location: California
 
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Mein Auto: 135i M Sport
Battery drain with top down

If I leave the top down the battery drains power and it won't start... takes about an hour or less. Any ideas what it might be? I don't have a schematic. No dome or other lights were left on.

Battery checked out good and the alternator is also good, putting out about 14v

Thanks,
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2012 135i M Sport Convertible (E88) 40k miles
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Old 09-12-2019, 09:02 AM
Markst Markst is offline
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One of the motors that fold the top?
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Old 09-12-2019, 09:26 AM
doane2u doane2u is offline
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Does anyone have a link to the wiring diagram for this E88? I don't hear any motors running.
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Old 09-12-2019, 09:43 AM
Markst Markst is offline
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Automatic soft top operation.
Wiring Diagram


You should probably start at the fusebox though, check the voltage difference between the fuses' legs, so you know which one is using current.

Last edited by Markst; 09-12-2019 at 09:49 AM.
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Old 09-12-2019, 02:45 PM
doane2u doane2u is offline
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Thank you, really appreciate it!
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Old 09-15-2019, 06:37 PM
CliffT CliffT is offline
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I suspect that the symptoms are just masking a weak battery.
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Old 09-15-2019, 09:35 PM
doane2u doane2u is offline
doane2u
Location: California
 
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It turned out to be a weak battery after all. It was just coincidence that the top was down several times. AAA had tested the battery and the indicator lens on the battery was green indicating it was good, along with the alternator being good, that really mislead me.
My mechanic replaced the battery and let it sit all day with the top up and down and there were no problems. Has been fine since Wednesday of last week. I am out several hundred dollars, but am glad it wasn't something more complicated.
Thanks everyone for trying to help
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Old 09-16-2019, 05:46 AM
jaye944 jaye944 is offline
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actually it makes perfect sense, using the top, takes a LOT of battery power, then it the car stays in standby mode for around 30minutes, so yes weak battery will get killed in short order
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battery, power leak, voltage leak


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