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2015 60aH REX
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Discussion Starter · #1 ·
My 12v battery died while the car was charging. No sweat, I replaced it, been down this road before.

Now my car starts up normally if I charge the 12v manually first, But the car can't make up its mind if the 400-volt battery is at 0% or 100%. The driver's screen shows 100%. But try to drive and nothing happens, then a notice comes up on the centre screen saying that the high-voltage battery is low and I shouldn't leave it like that.

I can't drive it because it is at 0%. I can't charge the car or turn on the REX because it is at 100%. And it is not recharging the 12v because it is at 0%

I've checked if I accidentally pulled out a wire when I shoehorned the new 12v in. Nope.

If this was a computer I'd do a hard reset to clear the registers. Any suggestions?
 

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Disconnect the 12v battery and charge it up off the car then reconnect, the 12v may be a bit low and the i3 doesn't like that.
 

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From what has been said on other i3 forums if your changing the new 12v battery it should be absolutely fully charged before changing it, usually then the new battery won’t have to be coded to the vehicle.

If the new 12v is up to spec and fully charged and still you have issues then it looks like you may well need the vehicle to be attached to the BMW system for coding, or at least someone who has access to the software.
 

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Discussion Starter · #4 ·
SOLVED: From a Facebook group, posted for reference:

Did you first disarm the HV system prior to replacing and fitting the new 12V? It’s quite important that the 12V be connected to the car only while the HV is uncoupled. Often, the DC/DC inverter stays active even with the 12V disconnected. It could also harm the inverter as it would then run on no-load which could cause many control units to lock up. Try disarming the HV system with the front interlock first, then disconnect the 12V. Wait about 30 minutes and only reconnect the 12V with the HV still disarmed. You should see the red HV warning on the cluster saying HV is unavailable. Then (while the car is OFF), rearm the HV. You should be good to go. The BMS should take a couple hours to recalibrate the 8 HV battery packs.
 

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SOLVED: From a Facebook group, posted for reference:

Did you first disarm the HV system prior to replacing and fitting the new 12V? It’s quite important that the 12V be connected to the car only while the HV is uncoupled. Often, the DC/DC inverter stays active even with the 12V disconnected. It could also harm the inverter as it would then run on no-load which could cause many control units to lock up. Try disarming the HV system with the front interlock first, then disconnect the 12V. Wait about 30 minutes and only reconnect the 12V with the HV still disarmed. You should see the red HV warning on the cluster saying HV is unavailable. Then (while the car is OFF), rearm the HV. You should be good to go. The BMS should take a couple hours to recalibrate the 8 HV battery packs.
Great update and you got it going, this will be useful as batteries are replaced for other owners.
 

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Sorry if you didn’t already know, but disarming the HV battery is a precaution you should take when working on anything electrical on the i3, it does no harm but stops odd issues like you had when changing the 12v battery.

I should not have assumed you had done this in the first place, my apologies.
 
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