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Suspected 12v battery dead.. Currently at service center. Happened right after getting a new coilovers set installed... also have a stealth hitch....

Aaf0052

Member
Sep 2, 2020
22
15
Charlotte
Hey so... I just had my sports coilovers from MPP installed by a highly reputable technician in the Denver area and when I went to pick up the car, it wouldn't start. Was able to open the doors and the windows would crack open each time i did. Contacted Tesla Roadside assistance and they said to try to restart it with the 2 scroll wheel trick. Didn't do anything. Windows are able to be rolled up but verrrry slowwwwly.

Couple minutes later, screen tries to come on a couple times (a couple mins apart each time) - each time, the screen lights and I see the T logo briefly, then the whole screen flickers off.

Roadside assistance called a tow and they tried to jump the car to put it on the the bed. I'd exited the vehicle and rolled the windows up (it was also raining this whole time), tried to keep the inside dry but it was a little worrisome... Interestingly the tow guy said the battery looked like it had enough charge. We also couldn't open the doors again, but could open the trunk. We left but they eventually towed the car to a service center... where it is now.

Couple weird things I've noticed over the past month or so, maybe unrelated:
- moderate humming noise (12v battery charging? idk) after parking the vehicle in the garage.
- error message saying something like "front passenger restraint not functioning"

Worried about warranty issues with a stealth hitch installed and now having to have it picked up from the parking lot of the place where I'd just got the coilovers installed

Sigh
 

stopcrazypp

Well-Known Member
Dec 8, 2007
10,820
5,754
Yep the tow package is somehow connected to the battery. Was wondering when I had it installed if that was going to cause issues
Note the Tesla has e-Fuses for the 12V connections inside the car. Not sure if it's exactly the below post, but I have read also Tesla is keeping tabs on power draw and if you draw from somewhere that it is not power budgeted (like direct from battery) that can cause issues too.
DC to DC converter: what can it reasonably handle in terms of using your battery as a power source?
You may find more info here too:
MASTER THREAD: Powering house or other things with Model 3 12V battery

I should also mention I just cracked 40k miles
I don't think the miles matter as much, but I believe for the earlier Model 3s the 12V battery dies out in around 2 years, although some have been able to go longer.
 
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limmerguy

Member
Nov 21, 2018
23
33
Bay Area, CA
Got it. I’m betting it is the tow package wiring harness then. It might seem like a trivial power draw, but my guess is that it draws enough power to drain the 12V battery into sub-prime territory between top-offs. The 12V lead acid is relatively tiny when compared to regular ICE cars.

If you want to save your 12V battery without pulling all the wiring out, you could pull the line fuse (should be near the 12V battery terminal) when the trailer wiring isn’t being used and that’ll prevent any parasitic drain.

I also have a stealth hitch with tow package, but I have the wiring harness hooked up to a hard-to-reach relay on the left body control module under the dash. It turns off when the HV battery disconnects
It supplies 10A and not much more. I’ve tripped it several times and resetting it is a mystery. It just comes back whenever it feels like it which can be between 45 minutes and 12 hours. Rebooting the car doesn’t reset the electronic fuse either.
 
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alexgr

Member
Aug 13, 2019
862
754
42
Couple weird things I've noticed over the past month or so, maybe unrelated:
- moderate humming noise (12v battery charging? idk) after parking the vehicle in the garage.
- error message saying something like "front passenger restraint not functioning"
1) Summer, heat, AC
2) Had the same thing, it is a lose seat connector harness, fixed at a SC.
 
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Dre78

Member
Dec 16, 2018
305
299
Chicago, IL
"Front left passenger restraint" is likely unrelated. There's a buried service bulletin affecting Model 3s; it should be addressed under warranty. I say "buried" because I intermittent received the error; but I didn't receive an email to owners that were affected, and no service bulletin exists for my VIN when checking online VIN Recall Search | Tesla Service. Regardless, Tesla SC fixed under warranty.

Good luck! Please keep us updated? We're 2-and-a-half years on the original battery, and considering preemptively replacing the 12v to avoid being stranded.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
10,371
11,714
Riverside Co. CA
"Front left passenger restraint" is likely unrelated. There's a buried service bulletin affecting Model 3s; it should be addressed under warranty. I say "buried" because I intermittent received the error; but I didn't receive an email to owners that were affected, and no service bulletin exists for my VIN when checking online VIN Recall Search | Tesla Service. Regardless, Tesla SC fixed under warranty.

Good luck! Please keep us updated? We're 2-and-a-half years on the original battery, and considering preemptively replacing the 12v to avoid being stranded.

I decided to do exactly that (on my own dime, since it had not failed yet, but my car is 2.5 years old, like yours). Total cost for a mobile ranger to replace the 12v battery in my driveway was $121 and change, "out the door". The battery is $85, the labor for installation was $29.25, and the rest is local tax.
 

Aaf0052

Member
Sep 2, 2020
22
15
Charlotte
Yeah I really wish I'd considered purchasing a backup battery.

The SC has had the car for almost 48 hours, and from the communications, sounds like they haven't been able to look at it yet (backlog of some sort?) they might have it over the weekend. It's the Littleton, CO location which I know has hit or miss reviews. I told the rep I was worried because the internal temp got to 140F yesterday (windows are all closed and they couldn't be opened when it was towed) and he said he would go out and "turn on the cabin overheat protection".... which...... isn't possible right? lol

Thank you all for the incredible info... yeah fingers crossed! I almost don't want to say anything about the seatbelt thing right now b.c. I just want the car back :D
 
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Aaf0052

Member
Sep 2, 2020
22
15
Charlotte
The technician found that our Model 3 likely needs a rear drive unit inverter. He's working with the engineering team right now to confirm, but the SC would need to order the part.

Super thankful that we have the loaner, its a 2019 model 3 performance with FSD and white interior which is pretty sweet. It is speed locked to 85 and chill mode
 

limmerguy

Member
Nov 21, 2018
23
33
Bay Area, CA
The technician found that our Model 3 likely needs a rear drive unit inverter. He's working with the engineering team right now to confirm, but the SC would need to order the part.

Super thankful that we have the loaner, its a 2019 model 3 performance with FSD and white interior which is pretty sweet. It is speed locked to 85 and chill mode
Wow, that's an unexpected diagnosis. Great that you got a loaner! I've only gotten a loaner once. Everything else was Uber credits (like, 3 times).

I wonder if the humming noise was from the inverter and not the usual coolant pumps? If you can recall, where was the humming noise coming from? The coolant pumps are near the frunk and the rear inverter would be at the rear/trunk space.
 

Aellinsar

Member
Aug 2, 2017
246
213
Ohio
The technician found that our Model 3 likely needs a rear drive unit inverter. He's working with the engineering team right now to confirm, but the SC would need to order the part.

Super thankful that we have the loaner, its a 2019 model 3 performance with FSD and white interior which is pretty sweet. It is speed locked to 85 and chill mode

Best of luck with your car. Mobile service is coming to replace my 12V battery today, but at least my car is still running (though yesterday had a bunch of scary error messages upon startup).

I've had a loaner twice from the service center (Model S and a Y) but neither were locked into chill mode.
 
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Aaf0052

Member
Sep 2, 2020
22
15
Charlotte
Engineering confirmed it needs a rear drive unit inverter replacement. They ordered the part and said it should be a couple days. I wonder (I know pretty much nothing about cars) if it has anything to do with plugging an acdc adapter in the cigarette lighter to charge my laptop every month or so
 
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stopcrazypp

Well-Known Member
Dec 8, 2007
10,820
5,754
Engineering confirmed it needs a rear drive unit inverter replacement. They ordered the part and said it should be a couple days. I wonder (I know pretty much nothing about cars) if it has anything to do with plugging an acdc adapter in the cigarette lighter to charge my laptop every month or so
That may affect your 12V battery or DC-DC converter, but I don't see how that would affect a drive unit inverter, which would run on HV, not the 12V system.
 

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