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2023.20.7 Bricked 2014 Model S

EDIT: False alarm, it was more than likely my 12v battery that failed during the update....

After doing a software update this afternoon, my 2014 Model S is undrivable and unresponsive.

Full details:
Got a software update notification this afternoon to install 2023.20.7 and so, as usual, I clicked the update and go about my day. I realize a few hours later that I never received an “update complete” notification so I go check on the car in the garage.

I notice the handles presented very slowly as do the mirrors when I press the handle to open. Both screens are off, and touchscreen is completely unresponsive. Hazards work, as do truck and frunk with the key fob thankfully but just about everything else is dead.

Of all the years of Tesla ownership, I’ve never had an update fail, much less brick the car in the process. I scheduled Mobile Service in hopes that they would be able to access the car and redeploy the software. Unfortunately, the soonest appointment is on the 18th… The S isn’t our primary car so we can certainly wait, but I’d really hate to wait 2+ weeks and then be told it needs to be towed to the Service Center. Service Center’s soonest appointment is the 13th so not too much better off…

Do you all think Mobile Service might be able to access the gateway and redeploy? Or should I go ahead, bite the bullet, and get it towed to the Service Center?
Last edited:
Call roadside assistance. Can you connect to it with the app? If no, they probably cannot see it either.

Sounds like a 12v battery would be a possibility. When was the 12v replaced last?
I was thinking of calling them to see what they recommended. No visibility in the app or via the API at all.

I could pull the frunk and get a multimeter on the 12v to see what’s going on.
12v was replaced in 08-2020 but I didn’t get any “low voltage battery needs replacement” or anything this time.
Call roadside assistance. Can you connect to it with the app? If no, they probably cannot see it either.

Sounds like a 12v battery would be a possibility. When was the 12v replaced last?
Pulled the frunk and feel really stupid now as the 12v was sitting at 10.3v... Looks like I'll have to grab a replacement and hope the car will recover on its own or at the very least. If not, hopefully Mobile Service can redeploy once the fresh battery is in.

Just really odd that I didn't get any warning of the issue, but hey, I don't expect consistency from Tesla lol
Yeah, double on the comment that, "There are many ways for 12V to fail". But a drop of roughly 2V does sound like a single cell in the 12V battery going bad.

Thing is: Say that the car's high-voltage->12V inverter isn't working so well. Say it's not charging the 12V battery. Said battery runs down. When one gets near zero charge, the six cells in a lead-acid battery don't have the same charge (manufacturing variations and such), so the weak cell is going to get reversed in potential while the rest are working. If one attempts to charge a battery back up after an event like this, the "inverted" cell doesn't always come back to life.

Which is why, with an ICE, running the battery down to zero and then trying to use the battery afterwards sometimes works, sometimes works for a while, then the battery dies; and sometimes it dies right off.

So, having somebody check the wiring around that 12V inverter might be a Good Idea. My 2018 M3 had its battery replaced back in 2019 (had a pyro fuse failure, Tesla replaced the 12V battery as part of the repair), and said battery is still going strong in 2023.
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Thank you all for the insight/suggestions!
Just in case this happens to anyone else, and to serve as a cautionary tale, please make sure your 12v battery is good before doing a software update, especially on older Model S'.

It was the 12v battery after all, and I had to get the MCU replaced along with it to the tune of $2k

Full Story:
After reading what you all mentioned about the 12v, I purchased a battery tender and hooked it up. The battery got up to around 12.5v and was holding steady, but when a load was applied, the voltage went down very quickly, especially if I opened a door or unlocked the car (the screens were still completely dead).

A few days after my post, Tesla changed my Mobile Service visit to a Service Center visit as they said it couldn't be done via Mobile Service. I coordinated a tow with my insurance and after 2 companies said they didn't want to try, a third finally did. It was incredibly tricky to get on the truck since the car couldn't be put in neutral and was tightly parked in my garage (thankfully the only casualty was a little chip in the paint on one of my wheels).

Tesla started looking at it this weekend and said it was absolutely the 12v battery and more than likely the MCU as well. When they contacted me to come pick it up yesterday, I was discussing with the Service Manager and the official story is, the 12v got low enough that the MCU powered off in the middle of the update and was "interfering with the functions of the gateway".

I just got the car back yesterday, just over a week later after the fated update. Despite everything, Tesla Service actually came through and mitigated some of the cost of this out of warranty repair. What was originally going to be a $3k+ billed was shaved down to just over $2k by the Service Manager who removed the diagnostic fee and comped some labor time/price of the MCU2 replacement.

Though the odds of this happening again are slim, not having a car for a week and acquiring a $2k repair bill has certainly made me aware of this as a potential future issue. Hopefully to mitigate this, I purchased a Bluetooth 12v battery monitor that I'll check periodically, especially before performing a software update to ensure the battery is up to the task.
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literally just had this same issue this morning in my 2020 m3

Thankfully yours looked like it either completed the update before the 12v failed or the 3 has some more robust failsafes in place to prevent MCU damage. So weird that it was the exact same update too!

Was yours the original 12v battery? If so, ours were probably around the same age, as I had mine replaced in 2020.

Did you still have MCU1 in your car? Was an upgrade even required?
I had MCU2 in my car, thankfully they had it in stock as the SC.