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One very confused i3

Posted: Thu Jun 23, 2022 12:27 am
by clasqm
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 or turn on the REX because it it is at 0%. I can't charge the car because it is at 100%. And it is not recharging the 12v because ...
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?

Re: One very confused i3

Posted: Thu Jun 23, 2022 4:34 am
by clasqm
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.

Re: One very confused i3

Posted: Thu Jun 23, 2022 8:11 am
by eNate
FB to the rescue!

This is good to know. I always thought the HV disconnect was recommended but not required. I had no idea it could result in this much chaos.

Re: One very confused i3

Posted: Thu Jun 23, 2022 4:01 pm
by alohart
eNate wrote: Thu Jun 23, 2022 8:11 amI always thought the HV disconnect was recommended but not required. I had no idea it could result in this much chaos.
BMW's TIS documentation indicates that with early integration levels (system software versions), if the HV disconnect isn't disconnected prior to disconnecting or externally charging the 12 V battery, problems could occur. It also states that the HV disconnect shouldn't be disconnected until the HV system goes to sleep on its own, which could be as long as 30 minutes after any action that would keep the HV system on like unlocking/locking/opening/closing doors, the hatch, or the frunk. The documentation states that these problems were fixed in an integration level update which occurred during the 2014 model year.

Even though our 2014 i3 was delivered with an integration level that should have protected against problems that might occur when the HV disconnect isn't disconnected before disconnecting or charging the 12 V battery, I was always careful to disconnect the HV disconnect after the HV system shut down on its own and only then would I disconnect or charge the 12 V battery. I stored our 2014 i3 for 3 to 9 months every year except 2020 and never had any problems. I just stored our 2019 using the same procedure and don't expect any problems.

Based on reports I've read about problems other i3 owners have had when changing their 12 V batteries, I'm convinced that not disconnecting the HV system or not charging a new 12 V battery fully before installing it can lead to problems that could be difficult to fix.