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12v battery failure, Unable to access frunk

MKurzdorfer

New Member
Jan 1, 2018
4
4
Woodbridge, VA
So it looks like my 12v battery is in its death throws today on my April 2018 M3 (50,340 miles :mad:). I received no warning messages (apparently like many other owners).

I drove home from work this afternoon and went to leave with my wife 2 hours later. The drivers side door opened, however, the passenger door wouldn't. The MCU was dark and the controls were non-responsive. The foot well lights were flickering. I attempted to open the frunk, however, the app no longer was able to communicate with the car. I did notice the sulfur smell so I was pretty certain this was the 12v battery.

I am like "I am ready for this". I grabbed my battery jumpstart pack and proceeded to pull off the tow hook cover. I attach it pack to the Pos & Neg wires and get no response from the frunk. I tried a fresh 9v battery as well, however, same results...no sound or action from the latch. What I do hear is this wind-up sound (repeatedly)(New video by Michael Kurzdorfer). I did disconnect the high voltage connector under the rear passenger seat.

Any other clues? Is it possible that the battery has "just enough" energy that it won't release the Frunk using the external power...Or is it possible there is something wrong with the wiring from the tow hook to the frunk latch?
 
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MKurzdorfer

New Member
Jan 1, 2018
4
4
Woodbridge, VA
Smells more like the pyro fuse blew.
So it looks like my 12v battery is in its death throws today on my April 2018 M3 (50,340 miles :mad:). I received no warning messages (apparently like many other owners).

I drove home from work this afternoon and went to leave with my wife 2 hours later. The drivers side door opened, however, the passenger door wouldn't. The MCU was dark and the controls were non-responsive. The foot well lights were flickering. I attempted to open the frunk, however, the app no longer was able to communicate with the car. I did notice the sulfur smell so I was pretty certain this was the 12v battery.

I am like "I am ready for this". I grabbed my battery jumpstart pack and proceeded to pull off the tow hook cover. I attach it pack to the Pos & Neg wires and get no response from the frunk. I tried a fresh 9v battery as well, however, same results...no sound or action from the latch. What I do hear is this wind-up sound (repeatedly)(New video by Michael Kurzdorfer). I did disconnect the high voltage connector under the rear passenger seat.

Any other clues? Is it possible that the battery has "just enough" energy that it won't release the Frunk using the external power...Or is it possible there is something wrong with the wiring from the tow hook to the frunk latch?
Looks like waiting overnight was the trick. I checked the car this morning and it was finally silent. I was able to get the frunk open with my jump pack (with booster). New 9 volt battery didn't work. Checked voltage on the bad battery. It was only 4v!

Off to find a battery (none of the area service centers are open on the weekend). I wish there was parts hours at least on Saturday.
 
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mrau

Authorized Driver
Supporting Member
Nov 12, 2018
452
858
Mid-Michigan
To openFrunk with a spare battery the car's 12 volt battery needs to be dead, if not dead then the car must be unlocked.

Not sure if you can still unlock the car if the 12 volt battery is "almost" dead. Maybe try it again with the drivers door open.

Also, there are two wires to hook up to the battery (positive & negative). Sometimes only one wire shows itself and you may have to fish out the second wire. I am sure you know this, but just covering all the possibilities. :)
 
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Timbo2

Member
Jun 8, 2019
219
173
USA
If you want to risk it you can use a trim tool and move the latch. The hood is aluminum so you don't want to bend it. And of course you risk scratching things.

How to open a stuck frunk on a Tesla Model 3

Mind you he is doing this with the thing half up. You can slip the tool under the fully closed lid, but it is a real PITA.
 

N54TT

Member
Aug 14, 2018
978
766
NY
Are you trying to open it with the HV connector in the rear disconnected? If so Re-connect it and try again with 12v source.
 

MKurzdorfer

New Member
Jan 1, 2018
4
4
Woodbridge, VA
Looks like waiting overnight was the trick. I checked the car this morning and it was finally silent. I was able to get the frunk open with my jump pack (with booster). New 9 volt battery didn't work. Checked voltage on the bad battery. It was only 4v!

Off to find a battery (none of the area service centers are open on the weekend). I wish there was parts hours at least on Saturday.
Sorry about the delays responding in the thread. Long time reader, first time poster (everything is moderated for me).

Note: The car was unlocked at the time of all this.
 
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dduffey

Member
Aug 26, 2015
399
314
Austin, TX
This same thing happened to me. 12v suddenly died, no warnings. It was too weak to turn on the HV, or pop the frunk, but had just enough juice to run some subsystems.

I could not pop the frunk. The battery needs to be "completely" dead for the tow hook leads to become active.
 

N54TT

Member
Aug 14, 2018
978
766
NY
This same thing happened to me. 12v suddenly died, no warnings. It was too weak to turn on the HV, or pop the frunk, but had just enough juice to run some subsystems.

I could not pop the frunk. The battery needs to be "completely" dead for the tow hook leads to become active.

I wonder in these cases if you connect a 12v and try to open the frunk through the screen….will it then pop the frunk open?
 

N54TT

Member
Aug 14, 2018
978
766
NY
The problem is that the tow hook area wires provide no power UNLESS the 12v is dead. It's a normally open circuit.
Gotcha. Just weird how a 9v to the tow hook wires can pop the trunk….but a 12v thats got enough to power some subsystems doesn’t have enough to pop the trunk. Should have a manual cable inside the car in these situations…instead of having to wait for the 12v to die…or removing the front bumper to get to the cable.
 

e645824

Member
May 15, 2021
135
190
USA
I have my new Oct. 2021 ...MF299xxx Tesla Model Y. I already know to replace my 12 volt lead acid battery soon with an Ohmmu.

However, I also want be able to get into the frunk if the 12v system dies. Getting in at home isn't the problem; I'm worried about getting in when I'm out stranded somewhere. So I'd wrap up a small battery and put it into the tow-hook compartment (where the frunk leads are). However, I've seen recent reports that a 9 volt battery doesn't work anymore -- Tesla is insisting on 12 volts. And I'd like to use lithium since they last much longer than an alkaline A23 12-volt battery. But I can't find a 12v lithium. Two 6v lithium would also do the trick but are hard to come by. Would two 9v lithium batteries in series work, or is 18 volts too much for the frunk relay?

I have to imagine that this is already a solved problem. Does anyone know of a solution to this issue that we all might run into some day?

Thanks,

Scott

--

MYLR | Red ext | White int | 19" | 5 seats | tow | no FSD | made/delivered Oct 2021
 

mrau

Authorized Driver
Supporting Member
Nov 12, 2018
452
858
Mid-Michigan
You can always test the 9 volt on your car to see if it works. Remember the car has to be either unlocked OR the car's 12 volt battery dead for the frunk leads to work. Some folks have tested with their car doors locked and it will not work. Security feature of the car.
 

e645824

Member
May 15, 2021
135
190
USA
I've ordered these items and will give them a try to see if one of them works to open the frunk. I'll use 10-year CR123 one-time batteries that are easy to find. In this serial configuration, 4 of them will make 12 volts.

https://www.amazon.com/gp/product/B07N56GQ95
https://www.amazon.com/gp/product/B08D74VWQK
https://www.amazon.com/gp/product/B0036QL1JY

714zHaWxYRL._AC_AA220_.jpg
51gbMcFVjBL._AC_AA220_.jpg
51jz-QHXvTL._AC_AA220_.jpg


Two CR123 batteries are about the same size as one 18650 battery, so I should be able to insert four CR123 3-Volt batteries into one of these serial holders to get 12 Volts. Then it *should* fit into the tow hitch compartment and I'll secure it to the black/red Tesla wires with a velcro strap. I would just need to remember to replace those CR123 batteries in 6-7 years.

Now, Tesla should wire-in a permanent solution so that the Tesla fob remote can activate something to apply 12 volts to the frunk relay. This avoids the whole issue of needing to open the tow hitch compartment. It would need a rechargeable 12V battery that charges from the 12 volt lead acid battery (so the small 12V battery is still charged when the 12V lead acid battery fails). Thus, a small 12V battery (with a receiver circuit; activated by the fob) is recharged by a 12V lead acid battery powered by a 400V battery. Somehow, the analogy with "turtles all the way down" comes to mind... ;)

Scott

Edit: oops, I just noticed that I'm in a Model 3 thread. Although this issue should be the same for most Teslas with the 12V lead acid batteries.

--

MYLR | Red ext | White int | 19" | 5 seats | tow | no FSD | made/delivered Oct 2021
 
Last edited:

android04

Member
Apr 1, 2016
515
526
Southeast Nebraska
I have my new Oct. 2021 ...MF299xxx Tesla Model Y. I already know to replace my 12 volt lead acid battery soon with an Ohmmu.

However, I also want be able to get into the frunk if the 12v system dies. Getting in at home isn't the problem; I'm worried about getting in when I'm out stranded somewhere. So I'd wrap up a small battery and put it into the tow-hook compartment (where the frunk leads are). However, I've seen recent reports that a 9 volt battery doesn't work anymore -- Tesla is insisting on 12 volts. And I'd like to use lithium since they last much longer than an alkaline A23 12-volt battery. But I can't find a 12v lithium. Two 6v lithium would also do the trick but are hard to come by. Would two 9v lithium batteries in series work, or is 18 volts too much for the frunk relay?

I have to imagine that this is already a solved problem. Does anyone know of a solution to this issue that we all might run into some day?

Thanks,

Scott

--

MYLR | Red ext | White int | 19" | 5 seats | tow | no FSD | made/delivered Oct 2021
I have two A23 batteries stored behind the tow hook cover because they fit inline in a ziplock bag. They are Energizer batteries and should last a very long time (you can replace them every time you replace the 12v car battery). Having two adds redundancy, and I've tested the A23 to work on my car when unlocked.
 

e645824

Member
May 15, 2021
135
190
USA
I have two A23 batteries stored behind the tow hook cover because they fit inline in a ziplock bag. They are Energizer batteries and should last a very long time (you can replace them every time you replace the 12v car battery). Having two adds redundancy, and I've tested the A23 to work on my car when unlocked.

Thanks, but I am specifically looking for lithium because of the 10-year shelf life. Basically I want to stuff it into the tow-hook compartment and not worry about it. I only found alkaline A23 batteries and those would die after a couple of years.

Scott

--

MYLR | Red ext | White int | 19" | 5 seats | tow | no FSD | made/delivered Oct 2021
 

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