Trunk pops open / trunk light drains battery?

[Philipp]

Hello all,

I often find my 2017 i3 REX with an unlocked trunk: it's visibly unlocked and you can just open it by hand although the rest of the car is locked. Sometimes, perhaps related, the alarm goes off. This seems to occur more frequently at my work than at home.

Has anyone experienced this issue and found a solution?

There is an additional concern: when the trunk unlocks, it seems like the trunk light comes on and drains the battery.

I recently found the batteries fully drained and replaced the 12V battery with a new one from Remy. Now, after some weeks without use, everything is fully drained once again. Can the trunk light be the thing draining it entirely or is it likely something else?

Thanks in advance!

Philipp

 

[EvanstonI3]

1: Your key FOB can "unlock" the rear hatch (trunk). This would be enough to cause the light to come on.

2: The light should not stay "On" forever. They normally all go off after about 13 minutes of inactivity.

3: If the 12v battery discharges to 12.0 volts, the car's main battery comes on to "boost" charge the 12v for One Hour. This is not documented "feature" but I have documented it on my own car with a Bluetooth 12v battery monitor. I find it hard to believe that the 12v battery could be completely discharged if the car's BMS (battery management system) is operating properly.

4: You state the "batteries" (plural) were "fully drained". Do you mean that the 12v AND the main batteries were drained?

 

[Philipp]

Thank you, EvanstonI3!

1: Understood. However, it seems like the trunk comes unlocked without the key button being pushed. I usually keep my key sitting on my desk idly, so it's untouched. Similarly, for no reason the alarm of my i3 goes off a few times per week.

2: That makes sense.

3: Yes, I read that before. That makes sense.

4: I wish I had better documentation. I am actually not sure. I will update once I find out the state of charge of the main battery this time around.

Fact is, I got a battery related issues last October (drivetrain error, and few days later completely dead 12V battery). In November, I replaced the 12V battery and now it is completely dead again (not even the car doors can be opened). Perhaps the BMS is broken? But I am not sure what the last state of charge from the main battery was.

 

[EvanstonI3]

check the 12v battery terminals to make sure they are not loose. By "loose" I mean the TORX 30 bolt that holds the battery adapter down can come loose. You may need to remove the bracket to get the battery out far enough to tighten them from the top if you do not have a small angled wrench.

The only other thing I can suggest is investing in a Bluetooth 12v Battery Monitor that allows you to track the behavior of the 12v over time. That's what I have been using for about a year now. The app will show you the state of the 12v over time while the car is OFF. This may be helpful in determining when and how it is draining. That link is the one I use.

 

[Philipp]

Thank you, I will check the battery terminals. And I now know that the HV battery was left with ~80% charge 3 weeks ago, so it should have a hard time to drain fully.

I'll also consider buying that voltmeter - pretty cool idea!

 

[alohart]

3: If the 12v battery discharges to 12.0 volts, the car's main battery comes on to "boost" charge the 12v for One Hour. This is not documented "feature" but I have documented it on my own car with a Bluetooth 12v battery monitor.

Since installing a 12 V battery monitor last October, I have noticed 4 automatic 12 V battery charging events. Our i3 frequently sits parked for a week without being driven during which time vampire loads slowly discharge the 12 V battery. As you wrote, these charging events last exactly 1 hour. However, on our 2019 i3 with its original November, 2018, system software, these charging events have been occurring whenever the battery's voltage drops below 12.5 V. This difference in behavior compared with your 2017 i3 might be due to a different system software version.

An automatic charging event can occur after not having driven for as few as 5 days. I think that as the battery ages, I should be able to detect decreasing battery capacity which would result in automatic charging events occurring more frequently. This would be a warning that I need to buy a replacement battery to have available when the battery eventually fails.

These automatic charging events should have prevented Philipp's 12 V battery from discharging completely unless the load is too high. I don't think that the trunk light would be such a load. I wonder whether automatic 12 V charging wasn't implemented in earlier system software versions. However, I believe that you and Philipp both own 2017 i3's.

I like your suggestion to check the tightness of the 12 V battery terminals and clamps because they have been loose on our i3.

 

[ronbot]

I just saw this listed a few days ago in either a BMW notification list of required software updates, or maybe an NHTSA list. Ask BMW about it.

I just found this... seems to say the tailgate/lift gate can be codes to. open only after vehicle is unlocked...
https://www.google.com/url?sa=t&source=web&rct=j&url=https://static.nhtsa.gov/odi/tsbs/2018/MC-10136344-9999.pdf&ved=2ahUKEwimzLe0k6L9AhVLADQIHc3CCNgQFnoECBgQAQ&usg=AOvVaw2idUHz5-KFlJnag0GZyeW-

 

[alohart]

I just found this... seems to say the tailgate/lift gate can be codes to. open only after vehicle is unlocked...
https://www.google.com/url?sa=t&source=web&rct=j&url=https://static.nhtsa.gov/odi/tsbs/2018/MC-10136344-9999.pdf&ved=2ahUKEwimzLe0k6L9AhVLADQIHc3CCNgQFnoECBgQAQ&usg=AOvVaw2idUHz5-KFlJnag0GZyeW-

This service bulletin appears to have been issued to prevent the opening of the trunk by unintentional pushing of the "open trunk" button on the fob by requiring the doors to be unlocked before the trunk could be opened with the fob. The fob of an early U.S. i3 (maybe only 2014's?) doesn't include a button that opens the trunk (hatch), so this problem probably doesn't affect these i3's.

However, the fobs of later i3's does include an "open trunk" button and could experience this problem. A different workaround, one that I have applied to our 2019 U.S. i3, would be to reprogram the "open trunk" button to be an "open frunk" button like on our 2014 U.S. i3. For i3's with Comfort Access, I don't understand the need for an "open trunk" button because the trunk can be opened by pulling its latch even when the doors are locked. However, this isn't possible for the frunk, so I find an "open frunk" button to be quite useful. This is the reprograming necessary:

BDC (Body Domain Controller)

Change behavior of key fob button 3 (short, med, long press of button)
30D0->RC_DEFAULT_IDG_3RD_BUTTON_LONG werte: 05 (open frunk)