Drivetrain malfuntion error with 12v discharged, start engine message.

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Well-known member
Jan 2, 2019
My car was working fine despite having the original 12v battery. (I have one on order, I swear!) I had the HV battery disconnect switch off to take a look at some scuffing through the stainless steel wire braiding that protects the cables between the HV battery EME. I futzed around off and on for a while before deciding it was fine, and turned the HV battery back on. I got a drivetrain malfunction error. The HV battery disconected message goes away, but it is not sending power to the dc to dc converter that powers the 12v. It's unable to drive. tried turning it off letting it sit, trying again later. Then i got a 12v draining while stopped message. It got down to 11 volts. I got the battery charged back up but it doesn't clear the errors or let it drive or even EVSE charge. I tried a obd2 scanner but cant get it to connect, engine has to be "on" which I guess I can't make happen without clearing the error? I downloaded obd Fusion app, cant get THAT to connect, but I CAN connect with bimmercode.....but it won't change anything that is usefull to me right now. I don't think there is anything physically wrong with the car. I very committed to not sending it to a bmw dealer. I don't mind spending money on tools that could help. I should be able to get the right scanner to connect, right?
The obd fusion app says that it IS communicating with the scan tool plugged into the i3 but is unable to connect to the vehicle. It tries a whole bunch of communication protocalls before giving up .
IF the 12vdc battery is unable to power the computers, things won't run. There is a phantom backup circuit that will slowly try to charge the 12vdc battery, so plug it in and see what happens after awhile (probably hours). If that doesn't work, disconnect the HV again and put a charger on the 12vdc battery and see if once it's back up, you can get things going.
I and several other i3 owners have occasionally not connected the high-voltage disconnect properly. The high-voltage disconnect plug wasn't fully seated in its socket even though it looked like it might have been. That prevented our i3 from entering the drive readiness state. I don't recall seeing a HV battery disconnected message, but I might have missed it. I disconnected and reconnected the high-voltage disconnect with a firm push to restore normal behavior. Might be worth a try…

With a 12 V battery voltage down to 11 V, you might have gotten unlucky to have had a 12 V battery failure at the same time as you were inspecting the scuffing. I don't know the minimum voltage required to close the high-voltage contactor. Maybe the voltage of your 12 V battery sags too far when trying to close this contactor. I have been surprised at the magnitude of the 12 V system voltage sag when the high-voltage system turns on in our 2014 BEV (e.g., when unlocking the doors). With a voltmeter in the auxiliary power port below the center of the dashboard for over 2 years, I've watched the voltage drop to as low as 11.9 V before the DC-DC converter turns on after a few seconds even when the 12 V battery's resting voltage is >12.5 V (all verified by measuring the voltage at the 12 V battery terminals).

This surprising voltage sag made me suspect that our original 12 V battery was failing more than 2 years ago. The service manager of our BMW dealer told me that this is normal i3 behavior. Seems to be true because our original 12 V battery continues to function normally. I do have a replacement AUX18L that I bought over a year ago sitting on a shelf waiting to be installed when needed.
Thanks Art! I agree the age of the battery was probably a contributing factor. After tring a few scanners that wouldnt connect, I tried the BimmerLink app, which worked and cleared the codes, and now the car works fine! Wasnt easy though, as the car kept trying to turn off as I ran bimmerlink! I will put in the new battery when it arrives in a week or two.