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What happens if you disable HV + 12V battery and close everything?

Dolemite

is my name
Sep 19, 2019
1,372
1,738
Seattle, WA
Does anyone know what happens if you disconnect the 12V battery, disable the high voltage battery, and shut the doors & hood? Does this mean you're SOL? I haven't managed to do this (yet).

Not sure how the dead 12V + auxiliary frunk opening "works." I know you can only open the frunk when 12V is dead, but must there be secondary power from HV for the car to "know" this? Also, not sure if "dead" = "gone" - would the frunk open if it's just... not there?

So many interesting new ways to screw yourself over with this car.
 
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I *think* that you can always pop open the frunk using 12V on the leads behind the tow hook cover.
Except you can't when there IS 12V power and the car is locked, for security reasons.

We plan to occasionally leave our M3 stored, unplugged, for several months. I intend to:

Open the frunk
Lock the car
Wait for the contactor to open (?)
Remove the 12V battery
Close the frunk

Put the 12V on a battery maintainer elsewhere.

Hopefully when we return, the frunk will open. The leads behind the tow hook cover are there! But I prolly should do a test run just to be sure 🤔
 

Candleflame

Active Member
Mar 9, 2015
3,692
2,011
QLD, Australia
Except you can't when there IS 12V power and the car is locked, for security reasons.

We plan to occasionally leave our M3 stored, unplugged, for several months. I intend to:

Open the frunk
Lock the car
Wait for the contactor to open (?)
Remove the 12V battery
Close the frunk

Put the 12V on a battery maintainer elsewhere.

Hopefully when we return, the frunk will open. The leads behind the tow hook cover are there! But I prolly should do a test run just to be sure 🤔

i wouldnt do that as this disables the BMS too. I would simply charge to 90% and leave it be maybe checking every 2-3 months (or use teslafi). Vampiredrain is low enough that you should get 6-9 months out of it. if you want to keep it to minimum you can attach a 12V battery charger to the 12v battery so it only wakes to to bms stuff.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
12,577
15,042
Riverside Co. CA
Except you can't when there IS 12V power and the car is locked, for security reasons.

We plan to occasionally leave our M3 stored, unplugged, for several months. I intend to:

Open the frunk
Lock the car
Wait for the contactor to open (?)
Remove the 12V battery
Close the frunk

Put the 12V on a battery maintainer elsewhere.

Hopefully when we return, the frunk will open. The leads behind the tow hook cover are there! But I prolly should do a test run just to be sure 🤔

One of the things tesla specifically says is to leave the car plugged in, especially when storing it for a long period of time. I think you need to modify your plan of leaving the car for "several months" unplugged to "several months" plugged in and set to 50%".

Otherwise, its likely that if you develop any issues with your HV battery, they wouldnt be covered, due to "abuse" ("abuse" because you would be doing something that is specifically different than what is described to do in the tesla manual).
 
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i wouldnt do that as this disables the BMS too. I would simply charge to 90% and leave it be maybe checking every 2-3 months (or use teslafi). Vampiredrain is low enough that you should get 6-9 months out of it. if you want to keep it to minimum you can attach a 12V battery charger to the 12v battery so it only wakes to to bms stuff.
Do you need the BMS operating when the battery is not doing anything?

The vampire drain estimates I've seen are quite a bit higher. Leaving it for a month, maybe two, might be doable though.
 
One of the things tesla specifically says is to leave the car plugged in, especially when storing it for a long period of time. I think you need to modify your plan of leaving the car for "several months" unplugged to "several months" plugged in and set to 50%".

Otherwise, its likely that if you develop any issues with your HV battery, they wouldnt be covered, due to "abuse" ("abuse" because you would be doing something that is specifically different than what is described to do in the tesla manual).
Yes. There are risks. But not everyone has a garage with power available. Certainly our Condo Parking spot doesn't.
 

brkaus

Well-Known Member
Jul 8, 2014
8,290
6,851
Austin, TX
From the Tesla published 12v battery swap procedure instructions.

402E7DEF-F3D3-485F-8B3A-D9D906205103.png
 
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Dolemite

is my name
Sep 19, 2019
1,372
1,738
Seattle, WA
From the Tesla published 12v battery swap procedure instructions.

View attachment 682274
lol wait... they mention "upgrading" to Ohmmu in the official literature? ****ing. Hilarious.

I came across similar stuff and that's sort of what prompted me to start this thread... Like what are you supposed to do, shut down the car at the airport & bring a 12V battery in your carryon? Assuming having both 12V + HV disabled even opens the frunk... which I'm going to find out later today.
 
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Proper door operation does require 12V, that window up/down bit. So I guess you could leave the 12V connected and manually disconnect the HVB contactor first. Then close the door.

But I thought it would be easier to open the frunk and wait for the car to sleep, opening the contactor by itself. Then disconnecting the 12V.

But I haven't done any of this myself... a bit scary 😨
 

Dolemite

is my name
Sep 19, 2019
1,372
1,738
Seattle, WA
Proper door operation does require 12V, that window up/down bit. So I guess you could leave the 12V connected and manually disconnect the HVB contactor first. Then close the door.

But I thought it would be easier to open the frunk and wait for the car to sleep, opening the contactor by itself. Then disconnecting the 12V.

But I haven't done any of this myself... a bit scary 😨
To do what? Totally "turn off" the car? I suppose that could work? Maybe? Open question is whether the frunk is openable w/ the battery entirely removed. Trying that later.

FWIW, none of this is scary... My car's sitting outside right now w/ the 12VB sitting next to me & the HVB disconnected. (It's doing some weird *sugar* & I'm "resetting" it - more on that in another thread.) I pulled the 12V, first, and then disconnected the HVB. The instant I took off the HVB connector, I heard the contactors open.

Just be sure not to break the clip - there's a gray part that acts as a lever that you have to pull sideways to "unlatch," first. Then put a towel or something over the port to avoid any weird stuff from happening.
 
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If you disconnect the 12V battery before the car sleeps, it will sense it and throw some errors and the car will not go to sleep (that's why it warns you that the HV battery is taking over). If you disconnect the 12V battery after the car goes to sleep (HV is disconnect open), the car will not wake up (because it hasn't proactively kept itself awake).

 
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Dolemite

is my name
Sep 19, 2019
1,372
1,738
Seattle, WA

Update: Answered my own question​


Happy to report that even with the frunk closed, 12V battery completely out, and HVB disconnected, the emergency frunk release still works. So if for some reason both were to die or have a major fault, you can still get in... Good news... otherwise I would've been extremely disappointed. Ended up opening it by lining up 4x CR2s I had lying around.
 

stopcrazypp

Well-Known Member
Dec 8, 2007
11,380
6,544

Update: Answered my own question​


Happy to report that even with the frunk closed, 12V battery completely out, and HVB disconnected, the emergency frunk release still works. So if for some reason both were to die or have a major fault, you can still get in... Good news... otherwise I would've been extremely disappointed. Ended up opening it by lining up 4x CR2s I had lying around.
Some people use a 9V which is more common and easy to find (although not sure if it still works, especially with the 12V completely disconnected, I haven't tried myself).
 

Dolemite

is my name
Sep 19, 2019
1,372
1,738
Seattle, WA
Some people use a 9V which is more common and easy to find (although not sure if it still works, especially with the 12V completely disconnected, I haven't tried myself).
Yeah I gave that a shot too and it worked - struggled a bit, but definitely seems like an option with a fresh 9V. You could probably line up a bunch of AAs and pull it off, also... but you'd have to figure out a way to string it all together.
 

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