12V Battery Fault

Malacandra

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For the past four days, upon starting my car for the first time, I’ve been getting this message. It doesn’t happen on subsequent trips during the day… it only happens after sitting overnight, unattached to the charger.

So I brought it to the local Ford dealer, who has three service people certified to work on EVs and none of them know what to do with this: they say it’s not in their service documents. Apparently there’s nothing amiss in the OBD2 codes. I’ve read on this forum of numerous other folks seeing this message, so it’s a little hard to believe that it’s not documented.

After calling into Ford, they’ve been told to hold the car for 48 hours without using it to check on the state of the battery… but the service manager is saying that the error may be spurious. WTF?

(BTW, I am not getting any FordPass alerts about this, as others have.)

Ford Mustang Mach-E 12V Battery Fault 879FFD21-F441-431C-8143-159B6FFF4AF0
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Ford Motor Company

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For the past four days, upon starting my car for the first time, I’ve been getting this message. It doesn’t happen on subsequent trips during the day… it only happens after sitting overnight, unattached to the charger.

So I brought it to the local Ford dealer, who has three service people certified to work on EVs and none of them know what to do with this: they say it’s not in their service documents. Apparently there’s nothing amiss in the OBD2 codes. I’ve read on this forum of numerous other folks seeing this message, so it’s a little hard to believe that it’s not documented.

After calling into Ford, they’ve been told to hold the car for 48 hours without using it to check on the state of the battery… but the service manager is saying that the error may be spurious. WTF?

(BTW, I am not getting any FordPass alerts about this, as others have.)

Ford Mustang Mach-E 12V Battery Fault 879FFD21-F441-431C-8143-159B6FFF4AF0
Hi there! This doesn't sound like an experience we want you to have with your Mach-E. Could you please send us a PM with your VIN and the name and location of your Ford dealer? I'd be happy to look into how I can assist you with this concern on my end.
 

louibluey

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I haven't reviewed the details in some weeks, but there are various times and ways the MME charges the 12V LVB by starting the DC/DC converter when the car is off, including when it is unplugged.

For some reason, when the DC/DC converter comes on to charge the LVB in some circumstances, it also immediately makes this message.

Probably some internal software accounting of factors like time between LVB charge, causes the software to think there is a LVB problem.

As best as I can tell so far, I think others have had similar experiences, the algorithm is not working correctly.

There are people with really serious LVB problems, such as are caused by failures of the hv junction box which lives inside of the hv battery enclosure (bottom of car). But, when those get serious enough, under some conditions, the LVB does not charge at all, and goes flat (dead).

To my mind, most of these 12V service messages should say something like, "hey there, I (MME) just wanted to let you know that I noticed your 12V LVB was a little low, so I charged it for you".

Now, if this is happening every day, you may have a constant load, something like the headlight off failure where the headlights run for some time after MME is turned off (just cycle them to off using the knob on the front console), or some other constant load.

There is a small less likely chance that you really do need a new LVB and/or that little BMS computer, the box on the negative battery terminal. However, most likely, everything is fine.
 

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A bit late perhaps but I wanted to share my experience.

In the last two weeks I was forced to stop along the highway. The car generated all kinds of error messages (from open doors to parkingsensors to loadsystem failures), than started going slower until I was forced to stop.

In both cases it turned out to be the 12v battery that was drained. Since all electronics and computers run on this battery, the car was basically dead metal, no matter how full the HVB was.

The first time the dealer changed the LVB thinking it was broken and therefore it did not recharge. That turned out to be wrong. The second time, with a new battery, same problem.

Now the weird stuff: I had no problem at all after more then a year driving. This issue started AFTER the latest update of the car software.

Does this sound familiar to anyone?
 

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09-SEPT-2022 after an update I now have a "12V Battery Fault Service Soon". I called the dealership and received the usual "Did you reset the vehicle". So frustrating.

UPDATE -- new to the forum and found other threads that state this is a poorly worded warning message informing you that the LVB was charged by the HVB while the car was parked. In my case I believe this is due to a newly installed OBDII tracker that I leave plugged into my car from SmartChargeNY.
 
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Mach-Lee

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A bit late perhaps but I wanted to share my experience.

In the last two weeks I was forced to stop along the highway. The car generated all kinds of error messages (from open doors to parkingsensors to loadsystem failures), than started going slower until I was forced to stop.

In both cases it turned out to be the 12v battery that was drained. Since all electronics and computers run on this battery, the car was basically dead metal, no matter how full the HVB was.

The first time the dealer changed the LVB thinking it was broken and therefore it did not recharge. That turned out to be wrong. The second time, with a new battery, same problem.

Now the weird stuff: I had no problem at all after more then a year driving. This issue started AFTER the latest update of the car software.

Does this sound familiar to anyone?
There could easily be more going on here than a 12V issue. You should send your VIN to me or other trusted forum members to check what’s going on.

One guy had the car die while driving because the positive battery terminal came loose. We haven’t seen that since. Your issue doesn’t sound typical.
 

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I got my car back from Ford yesterday 10/5 after they swapped out my 12v. This morning I got the same message again. I’ve had this error message for months.
I also got another message which scared me and I took it to ford. It really is annoying to have a car this beautiful and techy with these problems. Then Ford service tech are new to this and they themselves don’t know what can be the cause.
Ford Mustang Mach-E 12V Battery Fault 43D6D9EF-EFCF-4748-94C7-92FED32C5E7D
 

Mach-Lee

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I got my car back from Ford yesterday 10/5 after they swapped out my 12v. This morning I got the same message again. I’ve had this error message for months.
I also got another message which scared me and I took it to ford. It really is annoying to have a car this beautiful and techy with these problems. Then Ford service tech are new to this and they themselves don’t know what can be the cause.
Ford Mustang Mach-E 12V Battery Fault 43D6D9EF-EFCF-4748-94C7-92FED32C5E7D
Brand new battery still doing it? Pretty sure this is another app polling drain. If you use any 3rd party apps that access car data like Optiwatt or Recurrent, that is the most likely cause.

Other people I've helped have had their 12V issues fixed after changing their FordPass password. That blocks the apps from polling the vehicle and fixes the drain problem. So try changing your password and I bet that fixes it.

Full list of 12V drain causes: https://www.macheforum.com/site/threads/how-to-recondition-service-your-12v-battery.11069/
 

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Thank you so very much Mach-Lee, that is very thoroughly written. I also sent it to my husband so he can understand what I want to do. I just finished changing my password so I’m hoping that fixes it. I also on the ford app changed the location permission to when using the app. I only open it when I’m going to use my car.
 

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In the last few days, I've been getting the "12v Battery Faut Service Soon" message too. And one day got the "Stop Safely Now" message when trying to start the car. Although on the 3rd or 4th attempt, it started properly. I was able to start it fine 10 more times that day as I kept checking it.

But today I didn't drive it. Checked it just now and got the "12V battery Fault Service Soon" message again. It only flashed for 3-4 seconds and goes away, and the car started fine.

Disconcerting, as we leave on a 2000 mile trip for a week Monday morning.

Up until now I haven't really had any significant problems in 27k miles. I just changed my FP password as a precaution. I'll charge the car more frequently, and start it more frequently, including remote starts. Although I really have no idea if those force it to charge the LVB. I do have a little cigarette lighter voltage meter plugged in all the time so check the voltage. I commonly get 12.3-12.7 after the car is shut off (where it presumably reads direct from the battery for the 10 miutes or so until the power times out), and 14.4 when it's running (presumably getting a feed from the HVB).
 

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In the last few days, I've been getting the "12v Battery Faut Service Soon" message too. And one day got the "Stop Safely Now" message when trying to start the car. Although on the 3rd or 4th attempt, it started properly. I was able to start it fine 10 more times that day as I kept checking it.

But today I didn't drive it. Checked it just now and got the "12V battery Fault Service Soon" message again. It only flashed for 3-4 seconds and goes away, and the car started fine.

Disconcerting, as we leave on a 2000 mile trip for a week Monday morning.

Up until now I haven't really had any significant problems in 27k miles. I just changed my FP password as a precaution. I'll charge the car more frequently, and start it more frequently, including remote starts. Although I really have no idea if those force it to charge the LVB. I do have a little cigarette lighter voltage meter plugged in all the time so check the voltage. I commonly get 12.3-12.7 after the car is shut off (where it presumably reads direct from the battery for the 10 miutes or so until the power times out), and 14.4 when it's running (presumably getting a feed from the HVB).
Do you use any third party apps/services that might be polling your car and thus draining your LVB? Do you have any accessories connected/plugged into the car, especially anything always on? Have you had the HVBJB s/w recall update applied? Can you check for DTCs? If not, I would suggest you provide your VIN on the FDRS thread so that someone can hopefully pull the codes for you.

Of course it is possible that the LVB is going bad...
 

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In the last few days, I've been getting the "12v Battery Faut Service Soon" message too. And one day got the "Stop Safely Now" message when trying to start the car. Although on the 3rd or 4th attempt, it started properly. I was able to start it fine 10 more times that day as I kept checking it.

But today I didn't drive it. Checked it just now and got the "12V battery Fault Service Soon" message again. It only flashed for 3-4 seconds and goes away, and the car started fine.

Disconcerting, as we leave on a 2000 mile trip for a week Monday morning.

Up until now I haven't really had any significant problems in 27k miles. I just changed my FP password as a precaution. I'll charge the car more frequently, and start it more frequently, including remote starts. Although I really have no idea if those force it to charge the LVB. I do have a little cigarette lighter voltage meter plugged in all the time so check the voltage. I commonly get 12.3-12.7 after the car is shut off (where it presumably reads direct from the battery for the 10 miutes or so until the power times out), and 14.4 when it's running (presumably getting a feed from the HVB).
My suggestions. Pack the 12V charger and an extension cord (in the frunk with the ford mobile). You already noted you drive with care. 12.7 but it would be nice to see them over 13. Need to watch it to see if it is draining itself I guess. Been there. If worse comes to worse you just double plug it with a 20 amp 12V charger.
 

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Do you use any third party apps/services that might be polling your car and thus draining your LVB? Do you have any accessories connected/plugged into the car, especially anything always on? Have you had the HVBJB s/w recall update applied? Can you check for DTCs? If not, I would suggest you provide your VIN on the FDRS thread so that someone can hopefully pull the codes for you.

Of course it is possible that the LVB is going bad...
No 3rd party apps. I leave the little cigarette lighter volt meter plugged in the center armrest all the time. Been in there for a year and a half. Seems to still be working OK so I doubt it's the problem (plus that power port disconnects after 10 minutes or so after the car is turned off anyway).

But, I do have an OBD2 that I accidentally left plugged in after a 2700 mile trip last month (monitoring battery temps when that was an an issue for some in the summer). I'm guessing that's what caused a vampire drain. Odd that it took a month of that before I started getting any messages tough. Anyway, I unplugged the OBD2 3 days ago when first getting the messages. Drove the car for a few hours since and the still getting a few of the messages. I guess it just takes many hours of ON time for the battery to come back?

After reading many pages of MachLee's long thread, I went ahead and started the car in the garage last night and left it running (turned the 30 minute shutoff off, turned off radio and climate and headlights, plugged into the EVSE, and left the fob in the car). What I don't know is whether that should provide a continuous charge to the LVB (mimicking the BatteryMinder method), or whether the car only kicks on LBV recharging "as needed" (thus may be well short of what it needs to give it a deep charge)?
 

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I think that whenever your cigarette lighter volt meter shows ~14 volts that that means the DC-DC converter is on. So if it shows that range of voltage, then it’s on.

I think.
 

dbsb3233

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I think that whenever your cigarette lighter volt meter shows ~14 volts that that means the DC-DC converter is on. So if it shows that range of voltage, then it’s on.

I think.
I think so too. Back in March 2021 when I first got the cig lighter meter, I was commonly seeing 3 levels:

12.3-12.6 battery only (like after the car was turned off)
13.5 which was assumed to be trickle/maintenance from DC-DC
15.3 which was assumed to be full LVB charge from DC-DC

I'm guessing an OTA somewhere along the way tweaked those a bit though. Now I'm seeing:

12.3-12.6 battery only
13.3 trickle/maintenance
14.4 full LVB charge
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