12V Power Reduced, Vehicle May Shut Down unexpectedly

12V Power Reduced, Vehicle May Shut Down unexpectedly

All of a sudden, this Notification pops up along with Car needs service and Car may not restart.

Reboots didn't help!

So called Tesla Roadside Assistance and they've towed away the car to a service center.

I miss my model 3 already. Anyone have any ideas what may be wrong?

2019.16.2 downloaded yesterday...

Lorenzryanc | May 31, 2019

Sounds like your 12v battery is dead. That battery runs everything but the drivetrain pretty much. Could just be a bad battery, but likely something with the charging system for that battery. The big battery charges the small one, small one runs most of your stuff. It shouldn't be a difficult fix and it has happened on occasion w/ these cars according to the forum. Hopefully you get it back soon.

Keep us updated when you get a solution!

synfendia | May 31, 2019

It could be the grounding bolt that has come loose. A few of us have had that issue, which causes the main battery not to keep the 12v battery charged.
Here is my experience:

rajivrag | May 31, 2019

Thanks guys. I will let you know once I hear back. It's waiting to get into shop.

blackiesdad | May 31, 2019

I had that message. After I stopped the car, it would not go into drive again - then things got worse. I ended up getting the car towed. The root problem turned out to be a bad high voltage controller board.

joe | June 6, 2019

Same situation exactly 2d ago. I need a new drive train...

rajivrag | June 6, 2019

Yes, that's the diagnosis I received today. The car needs a new rear drive unit and fuse. It's scary.

viharri.plv | July 21, 2019

I also faced the similar issue on 20/July/2019 yet to know the reason. Wasn't able to start the car after I got that message. Had to tow my car to service center.

CaliforniaMaki808 | July 22, 2019

I just got those messages today (July 22, 2019). How long will it take for them to fix it?

brownteeth | July 25, 2019

We had the same issue 1 day after getting it home. They said it was a loose wire going to the 12v battery

CaliforniaMaki808 | July 26, 2019

These are the parts Tesla will need to replace to fix this problem...5 days later and they called me at 4pm (Friday Jul26) to let me know my car is ready for pickup. They close at 6pm; website says they are closed on weekend but the invoice says they are open on Sat and Sun. Called them and left them a message at 4:30pm but they never picked up the phone so it'll be another day for me to pick the car up. Hopefully they will pick up tomorrow morning (it's Saturday Jul 27).


I wonder how much these parts are.

Tronguy | September 11, 2019

Sheesh. So, I've been hanging on these forums seeing the occasional, "My car did this!" and thinking, "Well, there's a lot of cars, occasional faults here and there, squeaking wheels get grease, and the actual failure rate Isn't All That Bad."
That works until it happened today to the SO: "12V power reduced, car may shut down unexpectedly".
Used the Roadside Assistance in the app; tow truck showed up in less than an hour; the guy tried jump-starting the car, no dice. The SO took a ride to the Service Center with the tow truck driver.
Others are right: No more loaners, just Uber vouchers. The car's in line for a diagnostic in the next day or so, at which point they'll know something. Based upon a quick Duck-duck-go search, the possibilities seem pretty varied:
1. Bad battery.
2. Bad battery cable.
3. Bad electronics to charge the batter.
4. Replacement of the drive unit (!)
5. Replacement of various controllers.
The car just crossed 10k miles a few weeks ago; we've had it for just under a year. Guess we'll find out if it's major/minor/what-have-you over the next day or three.

bp | September 11, 2019

@Tronguy - sucks, sorry (and worried) to hear it. Please post an update when you find out what’s up.

Tronguy | September 19, 2019

So, the saga continues. It took a couple of days for the car to move up in the diagnostics queue. So: Car went in on Wednesday, got diagnosed on Friday. Some fumbling around making sure the SO's phone (which receives texts) rather than the house phone (which can't) was on the repair ticket. The first Uber voucher expired on Friday; the second on Monday, the SO got another extension on Monday.
On Tuesday, we get word: Waiting on Tesla Engineering for further diagnostics. And was invited to come on down and get a loaner. Which was done. (The SO is driving a Model S now..)
On Wednesday, we get a text: Diagnosis complete. Pyro fuses in the battery pack have blown (!), and they're waiting for parts at the moment.
Wowzers. Possible bad battery pack. Now, the SO hadn't been driving the car before it failed: It had been sitting in the garage, without the charging cable plugged in, even. Walked out in the morning, tried to turn it on, and there was the message.
Pyro fuses.. By the name, those would be fuseable links that open up when it gets too hot. Methinks we don't have a burnt-down house thanks to said fuses. Again, wowzers.
Be interesting if they replace the entire battery pack or portions of same.
More to come.

markcohen | September 19, 2019

I had this issue 3 weeks ago. Got the message while driving near home. Turned around and called roadside. They told me to reboot and if the message went away, all would be ok. I did and it was fine for a day then needed to be towed. The SC replaced the battery and said that they checked everything out and all was ok. Well... took the car on a road trip with a destination 1000 away. About half way it decided that it wouldn’t supercharge any more. They told me to limp along on destination chargers. I did. We had just started on our way back when all hell broke loose. Long story short, the car first spit out loads of error messages - Car needs service, may not restart; 12v battery low please replace; Emergency braking may not work; Car shutting down; and more - then it totally died. We are now waiting for a tow truck and the rental car to take us the 200 miles to the nearest SC.

markcohen | September 19, 2019

I had this issue 3 weeks ago. Got the message while driving near home. Turned around and called roadside. They told me to reboot and if the message went away, all would be ok. I did and it was fine for a day then needed to be towed. The SC replaced the battery and said that they checked everything out and all was ok. Well... took the car on a road trip with a destination 1000 away. About half way it decided that it wouldn’t supercharge any more. They told me to limp along on destination chargers. I did. We had just started on our way back when all hell broke loose. Long story short, the car first spit out loads of error messages - Car needs service, may not restart; 12v battery low please replace; Emergency braking may not work; Car shutting down; and more - then it totally died. We are now waiting for a tow truck and the rental car to take us the 200 miles to the nearest SC. | September 19, 2019

@Tronguy - No idea why the Pyro fuse went. These are designed to protect the car from a major HV short, sensed by the electronics. The electronics fires the Pryo fuse far quicker than a conventional fuse, as used in pre 100 S/X. The pyro fuse is a clever solution to allow far more currents in high-performance modes. They are not tripped by heat, like a conventional fuse. So perhaps the Pyro fuse has a defect or the electronics tripped it incorrectly. This is a very rare issue and they need to figure out what actually went wrong.

markcohen | September 20, 2019

Mine was taken care of today. It was also the rear drive unit that had to be replaced. They said that an intermittent short in it caused all of the problems that I had with the 12v battery, supercharging fails, and ultimately the car totally dying. So far it seems to be working... we have our fingers crossed.

Tronguy | September 25, 2019

Well, my saga is over. The car was retrieved from Tesla this morning: It's been in the shop for 14 days. Final things replaced:
1. Pyrotechnic Battery Disconnect.
2. Harness, HV Battery-High Voltage Controller. (The harness was replaced, not the HV battery or controller, I think.)
3. Battery - 12V

Documentation says that "Vehicle has been diagnosed as need the Pyro fuse and penthouse harness replaced.". Nothing about the 12V battery fault itself, but maybe it got discharged beyond all redemption.

I did look up the business about the pyrofuse. Ta-Da! It's a Tesla special, they got a patent on it. It's actually kind of interesting in its own right.
First: Sulfer Hexaflouride. As it happens, on utility high-voltage, high power transmission lines, there is the occasional need to break the power connection with a big-ass mechanical switch. That's cool, but we're talking 10 kV+ here. If one has a 1" gap, the air will simply break down and one will have an arc that will last indefinitely. Even with a one foot gap, it's major lightning bolt arc city, indefinitely.
So, to fix this problem, there are canisters of SF6 gas that has a _much_ higher breakdown potential than air; when the switch is popped open, the canister lets loose and blows the arc away from the contacts until the contacts are far enough apart that normal air can keep the arc from re-forming. After a couple of these, they send out a lineman with a new set of SF6 cartridges and the power company is all set to do it again. Oh, yeah: some of these switches are operated by shotgun shells, the better to get them open in a Great Big Hurry. Fun.

The pyrofuse, the specific type apparently used in the M3 Tesla, serves a similar purpose. It appears to sit on the high-voltage, high-current output of the main battery pack. It's got a normal fuse in it. When said fuse opens.. It's not clear from what I read, but take your pick: Either the heat of the arc or the voltage across the fuse fires off the pyro charge, which then blasts away with something that presumably like air and not conductive, suppressing the arc so it quenches.

My guess: The wiring harness developed a short which blew the pyro fuse. As to why this took the 12V battery with it, durned if I know.

Don't know for sure, but I suspect a bullet was dodged. Anything that draws enough current to blow that pyrofuse could, if said fuse wasn't there, probably heat stuff up enough to be dangerous. But that's why fuses exist, anyway: It sure isn't Star Trek, where every time a spaceship takes a hit the consoles light up in sparks, fire, and smoke: You'd think that the Federation engineering department would _know_ about how to fuse stuff so junk just goes "click" with no drama when a fault develops. (But then we wouldn't have the drama, would we?)

Finally: As a couple of others have mentioned, there's apparently a service bulletin out on the charge port pins. The "Charge Port Pin Deadfronts" were replaced as per bulletin.

And they updated the software to 2019.28.3.1. Cool.

terminator9 | September 25, 2019

I had the same thing. The difference was the car kept on driving with that message and beeps. Took 3 service center visits, a total of 12+ days and a lot of uber vouchers.

First visit - can not diagnose the issue as it does not come up on the screen all the time.
Second visit - let's change the battery anyway and see if that fixes it.
Third visit (the longest) - The charging circuit was bad and it was replaced.

Error message hasn't come up after the third visit. I was starting to think this might be an unfixable problem but was glad when it was fixed! It was fun for me to go to the service center for the first couple of times for the experience but after three for the same issue, it was starting to get a bit frustrating.

dorakuss | September 25, 2019

Damn, just joined and waiting to pick up my new M3 on Friday! Sure appears to be a lot of horror stories here? :( Hope I didn’t make a bad decision???

Lorenzryanc | September 26, 2019

@Dora. This car is MY best decision in a long time and 1.5 years in with no regrets (cept maybe not waiting for the performance). There could be a problem with a particular car, but I don't feel its an epidemic. If you do have a problem, it'll likely poke its head out quickly. I want to stress, read the manual first. There's a LOT of features in this car and people are often confused when the car clunks while charging, or their steering wheel shakes on the road, or I have a tire pressure warning at 38 PSI. We'll be here to help with questions though! :) Enjoy the new ride

Magic 8 Ball | September 26, 2019

@Tronguy Nice that you are back in your car and they put you in a loaner eventually.

@Lorenzryanc The stories here are a tiny and biased sampling of overall ownership experience. There are over 300K happy owners on the road and growing.

Magic 8 Ball | September 26, 2019

Oops not @Lorenzryanc above was meat for @dorakuss

Tronguy | September 26, 2019

@dorakuss: I vote with M8B as regards the frequency of reports on Bad Things Happening to vehicles. Heck, take ICE cars: There's always been a significant but small percentage of ICEs that develop a dead motor, or a dead transmission, and I'm talking flying crankshaft/piston rods/cracked caes/etc. here. This usually happens, if it does happen, during the warranty period and is likely the _reason_ for a warranty period. For that matter, pretty much any ICE car I've owned has had extended warranties on the power train that go 'way out there.
Heck, 12V batteries, with which I'm familiar, always come with warranties: It's not uncommon to have infant mortality (and that really is the technical term) with those things, but the likes of Walmart and Autozone won't even blink if one brings back a battery bought a week or month previous that failed. Heck: My Prius had its 12V battery die at 20,000 miles; the replacement is still going strong at a 130,000.

So, do a search on "blown pyro fuse" on the web and you won't find much. The reasoning go like this:

1. Ma and Pa Sixpack are barely aware of the web, forums, and stuff like that; that's the majority of the people out there. So, faults on their cars get reported to the dealership/SC/whatever, but you'll never see their stuff on the web. My personal opinion: This class of owners probably comprises 85%+ of the population.
2. Of my personal estimate of 15% of owners who are on the web, maybe 5% of them (total: .15*.05 = .75%) are on the forums and communicate with other forum owners. But it's an easy guess that of that 15%, 85% of them will sign right up to complain when something bad happens. So, call that the complainer class: That'd be 0.15*0.85 = 1.2% of all owners will complain when something happens.
3. Result: In every auto forum I've hung out in, something like 15% of the posts have, "This thing failed!", and it's a one-time in and out for the poster. Well, most of the posters with real trouble will hang around until their problem is fixed, but then they're gone.
4. The regulars almost _never_ have problems because, well, most cars, as M8B states, don't have trouble.

Which is why my post, added on to a previous in-once-and-out-again thread, is odd. I'd like to think I'm a regular, but it's odd that the God of Statistics came down and bonked me one. The M3 has about 10K miles on it; but there's plenty of posters on this forum that have 'way over 100,000 miles and haven't had any problems at all.
Chalk it up to a warranty period failure and continue.

Finally: One can tell when there really _is_ a problem with a particular part or assembly on a car: The dealer stocks the part. My pre-Prius car, a 2002 Civic, had a no-kidding turn-signal/headlamp switch failure, a module mounted into the steering column. My son (who owned the car at the time) and I pulled out the maintenance manual and schematic and started troubleshooting. An hour or so of running back and forth with a voltmeter/ohmmeter got us to the turn signal/headlight stalk; 15 minutes of minor cussing got it off, and some quick checks with an ohmmeter determined that the thing was a deader. On a Saturday afternoon in 2010 we found a Honda dealer in Staten Island that had an open parts department, and they had the module for an 8-year-old car.
Ha. Three months later I got the recall notice in the mail for the part, along with an offer to get reimbursed for any repairs already done.

EPluribusUnum | October 5, 2019

I had this error message today, likely caused by some shenanigans I had performed during a trailer harness project, and the error reset after a sleep (reboots did not help). So don't immediately leap to any horrible conclusions if you see it. Definitely try a sleep before you panic.

TickTock | October 6, 2019

Same here. I was also knee deep in shenanigans and got the message. Was gone when I woke the next morning.

SteveWin1 | October 29, 2019

Just got the 12V error message today as well. The car managed to start and got me home from work, but now it will not start anymore. SO is out of town with the ICE and the Tesla will no longer drive and will not charge. Climate control won't even come on. Additionally, I can't schedule service because their app is glitching and it appears there is no way to schedule service using their website. Chat is not available. When I call their customer service number I am told (by a robot) that there is no way to schedule service on the phone and to use the app and that if I'm having trouble with the app to visit their support website for more information. There are still some service centers in California open (I'm in Florida), but when I call them, I'm immediately forwarded to the same robot I get when I call their main number. So basically I have no way to get this fixed.

$82K well spent! /s

httran26 | October 29, 2019

In a bind, you can try charging the 12v battery with an external charger.
The same issue happened to my brother's car. I told him to charge the 12v battery. The problem when away for 2-3 weeks and then the error message started popping up again. Got the battery replace by mobile service and all is good now.

SteveWin1 | October 29, 2019

thanks httran26. I may try that.

Tronguy | October 29, 2019

@SteveWin1: For what it's worth, when the car first failed with that error message, both the tow-truck driver (with instructions from Telsa) and the SC both tried to charge the 12V battery externally to see if that would clear the fault. That failed.
The way I read the error message: Something has prevented the 12V battery from getting charged and the battery voltage is low; that trips the error message.
In my case, it appears that a wiring fault caused a short that in turn blew the pyro fuse, disconnecting the main traction battery from everything, including the little inverter that charges the 12V battery; no charging, low voltage, and there one is.
Other things that caused this trouble that comes up if one searches for the error message: Busted 12 V charging module; busted ground wire to the battery; busted traction unit (probably shorted and blew the fuse); and you get the idea.
On top of all that, a bad 12V battery, a Thing That Happens, could also cause the fault. So, might be something simple, maybe even just tightening down a clamp somewhere, could clear the problem. Or it might be something more fun.
Good luck!

Tronguy | October 29, 2019

Oh, yeah: I'm in the middle of a +1000 mile vacation driving trip with the car, chasing up and down the East Coast. No problems, drives like a charm. So the fix appears to have worked.

Scrannel | October 29, 2019

I'm sure this has been asked, but has this been happening across a range of cars, or one version -- such as RWD, etc.?

SteveWin1 | October 29, 2019

Mines a Performance, although that name is a little ironic right now since it won't move at all.

SteveWin1 | November 1, 2019

Well, looks like I've got the same issues as @rajivrag and @markcohen. There is an "isolation fault (i.e. an internal leak)" that somehow has something to do with the rear drive unit. They've got to order a new rear drive unit for me and need to replace the wiring and the 12V battery.

Anyone know what the rear drive unit has to do with the 12V battery? My service advisor said in an email that they had to revise the drive unit "due to a trend with this concern" and that "this process does kill the 12 volt battery." She didn't explain how or why.

Thank goodness this happened before the warranty was up. Driving the toyota corolla rental they gave me is freaking hilarious!! I think Toyota mixed up the "go" pedal with a "noise" pedal. haha. Makes me miss my baby!

Tronguy | November 1, 2019

@SteveWin1: My reading of the fault and, well, just _thinking_ about it leads to the same conclusion: The 12V battery isn't charging, runs low, and some voltage detector puts up the error message.
"Isolation fault". Ha, and double Ha. "Isolation" is when current doesn't flow to places it ought not to go. When things aren't isolated.. When something is isolated, resistance is in the GigaOhms. When it's not isolated, we can be talking anything down to Zero Ohms. That is, it could be shorted.
If something high-voltage-ish is shorted, then one isn't going to get a charging battery.
On the other hand: It's completely believable that Tesla has a sensor of sorts looking for Leakage Current That Shouldn't'a-oughta-been-there, and, when it finds that, opens contactors left, right, and center to prevent a bad situation from getting worse. (Sorry: Contactor = Big Ass Relay That Can Carry A Lot Of Current and handles High Voltage.)
Now, as far as the 12V battery goes: If that battery's not being charged by the off-line big traction battery, it's going to discharge since the computers and all that jazz are still live. Take a lead-acid battery with six 2-and-something volt cells and discharge it All The Way Down. Since probability theory says that no two cells will have the same charge, that means as the battery discharges some of the cells are going to discharge all the way to Zero, reverse polarity, and keep on conducting current while the ones that still do have charge pump out current. Reversed polarity cells like this can get (a) weakened, never holding a full charge again, and/or (b) never hold any charge forevermore. Which is why if you've ever fully discharged a car battery to the point of having to jump the car, you may or may not get your battery back, and, if you do get it back, it may not be long for this mortal coil.
(Back in the day, I've had a dead car battery that, under charge, had 9V. Or 10V. Time for a new battery.)
Given that this is the case, Tesla's probably throwing in another $30 or so, wholesale battery cost, at the problem that they're already spending a couple of grand upon, in the hopes of Not Seeing You Again In The Near Future.

SteveWin1 | November 1, 2019

Thanks Tronguy

8141mail | November 8, 2019

model 3

SteveWin1 | November 10, 2019

I've got a question for you guys/gals.

I got my car back with a new rear drive unit, some new wiring and a new 12V battery. Despite the inconvenience of not having my car for a little over a week, having to deal with getting a tow truck, rental car, driving for hours to go get the car again, etc, I now have a brand new, re-engineered rear drive unit and a new battery on my 1-year-old car, so it feels slightly more new.

The problem is, I paid a lot more money for the Performance Model 3. Back when my car was being built in the "tent," Elon mentioned that performance cars were getting special treatment when it came to which motors they get. They were supposed to get motors that tested better than others, to make sure they can handle the extra demands and perform appropriately. My invoice from Tesla shows just the regular model number for the rear drive unit -- nothing special indicates that its also one of the "binned" performance drive units. I actually don't think there are different model numbers for different "sigmas" of motors.

After having to have my car towed because of a problem with my rear drive unit, after Tesla specifically said that the dual-motor model 3s would be able to drive with a one-motor failure, I wonder how true their other claims are and I wonder if there really was any preference given to performance cars. The fact that this isn't mentioned when they replace the parts makes me think maybe that was bogus as well. Should I contact them and make sure I got one of the "special" motors? Anyone think that was actually a real thing?


fahmihermawan175 | November 12, 2019

hello, I want to ask, I have succeeded, indeed the sim card in MCU Tesla model 3, but it doesn't work, does anyone know how to get the sim card to work

ellouno | December 6, 2019

I just had this sudden shutdown and slew of messages about the 12v battery reduced, automatic emergency braking is disabled, car needs service after I took delivery less than a week. Luckily cop showed up to block the traffic, not so much fun to create traffic during rush hour on Friday after when everyone is going home.

Since I have the car literally less than a week with 300+ miles, thinking if I should return the car. I still love and enjoying driving it. Finally it got tow to the SC and waiting to be diagnose.

Magic 8 Ball | December 6, 2019

@jimmylu2016 They will fix you right up, no need to worry about anything. You experienced a rare infant mortality of a component (possibly 12V battery) and they will replace it. This is not common and it would bum anyone out. Hang in there you will be back in love in no time.

vmulla | December 6, 2019

You have an option to get into a new car, or you have an option to use Uber credits while your car is in service.
If they can put you into a similar car immediately then I'd recommend getting a newer car. If it means long wait to find another replacement car then I'd recommend getting the car serviced.
Whatever it is make up your mind fast.

Mr.Tesla | December 7, 2019

You had just brought your beautiful new foal home when she fell ill. Instinctively, and without hesitation, you took her back to the veterinarian to receive the care she needs. After some recuperation, she'll be getting released for a second homecoming. In a short time, you'll find yourself glancing down at her with admiration, and chuckle about that fateful day, as she dutifully hurls you through space at 70+ mph. An ever vigilant protector, defending you from the marauding mongrels of the open road.

High-O Midnight Silver!

vmulla | December 7, 2019

What did you end up doing?

sbeggs | December 7, 2019

Nice writing style!
Since we've greatly missed Code Orange, you have the ability to delight us with your pen in that, please carry on.

dstevens | December 15, 2019

Got the same issue showing on mine.
Collected her on Thursday last week after many delays.

Had to collect 150 miles from where I live as they sent it to the wrong collection centre (Birmingham not Heathrow) Should have been 30 miles away.

On collection where no one even showed me around the car or any type of handover which I had heard about, the car was also in the wrong name. It was down for someone I'd never heard of.
Upon driving away after I had to drive it out of all the cars strewn on the forecourt I noticed the tracking was off and steering wheel misaligned and couldn't be bothered to go back to them to sort. As my experience had not been great so far.

Dived into a tyre place so they could sort the tracking. Then had to charge as not enough to get home, bearly enough to get to nearest supercharger.

Got it home and plugged her in showed the family.the gadgets and so on. Next morning started getting the "12v power reduce, vehicle may shut down unexpectedly" car still runs at present but for how long?
Done all the usual resets, and battery disconnect but still pops up message every 10-20 seconds. Haven't gone any distance yet as don't trust it to get me there!

All in all a fantastic buy!!??

Tronguy | December 15, 2019

@dstevens: this is why cars have warranties. Call the Service Center and (a) get the car in for service and (b) complain like mad.
The SO and I got our car back in 9/2018; we did get a bit of a "here's how the car works" from the delivery specialist, but nearly the first thing out of his mouth was, "Have you watched the videos on Tesla's web site?" When we answered, "yes", he showed us just a couple of things and left us to adjust mirrors/steering wheel/etc. while he helped other people. They're people, they do get overloaded.

Tronguy | December 15, 2019

@dstevens: And, just to double check your status: That warning message about low voltage seems to be, based upon my and other peoples' comments, an indication that your 12V battery isn't charging. That's pretty serious and you likely won't be going anywhere until it's fixed. If the car is within the one-week return time, time to start thinking about maybe returning it and getting a better working one?

dstevens | December 16, 2019

Well didn't get far today. Drove message blinked a few times but went away. Had a service call booked with Tesla but no one called back after chasing 3 times.
Went to drive home and made it 5.miles before shut down. Managed to drive in retail park to get of the road where I am still sat now after 3 and a half hours waiting for tow truck.
Tesla said they would bring car, bone available so longer wait for 3rd party tow firm. They will be here in 1-2 hours. Hire car company are bringing a car this won't be here till after the car has been towed so wait in the cold and rain till they arrive.
All in all hasn't really been the best start to my experience of Tesla ownership.
To add insult to injury they phoned up today to say that my car was available in Heathrow!!
You couldn't make it up!!!!
One week return, please tell me this applies to lease cars as well??

Oh she has just totally died. No power at all. Going to be fun trying to get it on the tow truck with no power to release the brakes!

dstevens | December 16, 2019

Only picked it up 5 days ago so heres to hoping I can return the piece for some other unlucky person.