12v Battery Fault - Service Soon

Mach-E VLOG

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I've been getting this message for a couple of weeks now. I am trying to schedule for my dealer to take a look at it and do the glass recall, but they are backlogged and windshields are back ordered. In the meantime, I'm trying to figure this out and decide if I should leave it parked until it gets diagnosed.

Basically, the first time I start the car for the day I get a "12v Battery Fault - Service soon" message. On other starts during the day, there is no error message. I have the little voltage monitor that plugs into the 12v outlet. When I first turn the car on, it is reading 14.5v. After the car is off, it drops to 12.5 to 12.9v (I'm actually trying to remember the exact numbers, but it was in that range).

Ford Mustang Mach-E 12v Battery Fault - Service Soon PXL_20220504_002416334.MP
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Mach-E VLOG

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If you can get your hands on a battery charger/maintainer it may be worth giving this a shot:

https://www.macheforum.com/site/threads/how-to-recondition-service-your-12v-battery.11069/

Did you happen to have your doors open/ACC mode running for a while? I had my doors open for quite some while in order to install a dashcam and I got this error a few times in the week that followed. I did the battery reconditioning and it seemed to go away.
Hmmm... The past two weekends I did. We took the Mach-E to a couple of EV events and had doors opening and closing all day. But I was getting it before that as well.
 

generaltso

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That poorly worded message just means the DC/DC converter is kicking on to charge your 12V battery. But if you’re getting it every day, there may be a drain somewhere. Getting a good long charge on your 12V battery to make sure it’s topped up is probably your best course of action.
 

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I've been getting this message for a couple of weeks now. I am trying to schedule for my dealer to take a look at it and do the glass recall, but they are backlogged and windshields are back ordered. In the meantime, I'm trying to figure this out and decide if I should leave it parked until it gets diagnosed.

Basically, the first time I start the car for the day I get a "12v Battery Fault - Service soon" message. On other starts during the day, there is no error message. I have the little voltage monitor that plugs into the 12v outlet. When I first turn the car on, it is reading 14.5v. After the car is off, it drops to 12.5 to 12.9v (I'm actually trying to remember the exact numbers, but it was in that range).

Ford Mustang Mach-E 12v Battery Fault - Service Soon PXL_20220504_002416334.MP
The fault probably indicates that at SOME point the 12v battery voltage dropped below 12v. This can happen maybe if you take lots of little short trips, or dont drive at all for a week or so. It is likely that when you get your windshield recall and software updates the internal charging modules will be 'fixed'.

The easiest way to make sure your 12v gets a good charge is to:
- leave your car 'on'
- disable the auto-off timer Setting so that is STAYs on
- and leave it on overnight.

The big HV battery will keep the 12v system up at 14.5v, and effectively charge your 12v battery. No need to use an external charger to re-condition or fully charge your 12v battery if everything else if working correctly.
 


hybrid2bev

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I've been getting this message for a couple of weeks now. I am trying to schedule for my dealer to take a look at it and do the glass recall, but they are backlogged and windshields are back ordered. In the meantime, I'm trying to figure this out and decide if I should leave it parked until it gets diagnosed.

Basically, the first time I start the car for the day I get a "12v Battery Fault - Service soon" message. On other starts during the day, there is no error message. I have the little voltage monitor that plugs into the 12v outlet. When I first turn the car on, it is reading 14.5v. After the car is off, it drops to 12.5 to 12.9v (I'm actually trying to remember the exact numbers, but it was in that range).

PXL_20220504_002416334.MP.jpg
I agree with @generaltso it's a normal, poorly worded, message. I got that same message, but more frequently when we were not driving as much. If you do frequent short trips the car is not "on" long enough to charge up the 12v. Drive the car for 20-30 minutes per day and I'd bet you'll never see this message again (unless there truly is an issue).
 
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I first got it after I got back from a 2 week trip where the car just sat at home. But I was got it after our trip to Vegas with 2 days of 13 hours of driving. I thought that would really be enough time to condition the battery if the time sitting had affected it.
 
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I agree with @generaltso it's a normal, poorly worded, message. I got that same message, but more frequently when we were not driving as much. If you do frequent short trips the car is not not on long enough to charge up the 12v. Drive the car for 20-30 minutes per day and I'd bet you'll never see this message again (unless there truly is an issue).
Drive the car more.... Best answer!!! :)
 

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My understand is your Mach-E is already up to date as you have Bluecruise. So something would seem to be consistantly draining your battery or it's one of the many Mach-E gremlins that only comes out sometimes and to some people. I leave a dashcam running in mine 24/7 (though it moves to timelapse in parking mode) and I've never seen a single error.
 

Neil4Real

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Dashcam drain or maybe you have that IPC bug where the IPC turns back on/doesn't turn off properly when you turn the car off?
 
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My understand is your Mach-E is already up to date as you have Bluecruise. So something would seem to be consistantly draining your battery or it's one of the many Mach-E gremlins that only comes out sometimes and to some people. I leave a dashcam running in mine 24/7 (though it moves to timelapse in parking mode) and I've never seen a single error.
Yeah, I have a dashcam but when this first happened I started to just leave it unplugged even though I had it for months with no battery drain issues.
 

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We do not know all of the software rules that lead up to this warning, there are some good guesses.

Despite what history gets you there, the warning itself is generated in some circumstances, the moment MME turns on the DC/DC converter to charge the 12V LVB itself.

Here is another quick example of a 12V service warning which just corresponds to the DC/DC converter charging the LVB. MME was in garage plugged in L2. I moved MME to the driveway (unplugged) at 12:22. At 12:37, I got the iPhone notification, service 12V battery (bogus). It probably should say something like, hey I noticed the LVB was low and topped it off for you.

Most of these indications appear to be generated by a faulty algorithm that does not properly account for the way MME does normal/regular care and feeding of the 12V LVB. That said, if you see this every day, there might be a problem, such as a continuous load, or a LVB measurement and/or charging problem.

In many cases, we have noticed that MME allows the LVB state of charge (soc) to cycle over a relatively large range, somewhat analogous to the way we use the hvb, then recharge it. We have seen many cases where LVB was allowed by MME to go below 50% before MME decided to charge it with the DC/DC converter. Note that regular discharge / charge cycles of the LVB may vary a LOT between us MME owners based on our specific driving patterns and use cases. It is also the case that some never get this warning, some get it several times a month, others somewhat more frequently. I would guess that daily might be a real problem.

Most of the time the 12 LVB is being charged by the DC/DC converter, the warning does not occur. In aux mode (FDRS users know this mode as "power on, engine off"), MME charges for about 24 minutes. I think this can be reset by turning MME completely off (not sure about the door thing, you could cycle them closed). At least through much of the winter, the DC/DC converter runs 100% duty cycle (always) when driving, there might be conditions where it does not, but it then will come on if needed.

For info, LVB soc is measured by that little box, the LVB BMS, on the 12V LVB negative terminal, and sent to other modules by LIN bus (the two wires of the connector on the BMS +12V and data, a "one wire" data system). The data is distributed from the master LIN module (it's been a while, I think it was BCM) is then distributed over one or more of the CAN buses. MME does use the LVB soc as reported by the BMS, that soc number is available on FORScan, FDRS, and with various OBDII monitors. Interestingly, LVB BMS also reports both LVB voltage data and LVB soc, many times a second when MME is awake, and once every 15 minutes when sleeping. An open question for me has been does MME do anything with the LVB voltage reported by the BMS, or does it only use 12V bus voltages measured at two or more other places in the system (other modules). I might get back to that question with warmer weather. I left off with a temporary mod, where I could vary the voltage measured by the BMS, but could not find that varying number yet on FORScan or FDRS data logging, but I forgot to turn off the DC/DC converter that was coming on too, and making the search more difficult (easily dealt with now by the hv interlock switch).

Final quick trivia note, The LVB BMS is powered directly by the 12V LVB. One terminal is the direct connection to the 12V LVB (the box literally connects to and lives on the negative terminal), the other, the small +12V wire that goes from the BMS connector directly to the +12V terminal tabs. So, especially in that recent case, where the #2 red wire came off the main fuse distribution, the only thing still running in the entire MME, was the LVB BMS.
 
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I have long suspected that a lot of these 12V messages are some kind of cumulative accounting, either rolled into the 12V LVB BMS soc number alone, or post processed later by another module, probably BCM.

For those with FDRS access, this new procedure may well solve (my guess, not a Ford directive yet) some of these 12V warnings. It's part of a larger procedure for module programming, so just skip the last step of connecting the power supply.

So, if I understand it correctly (have not tried it yet):
1) charge 12V LVB to 100%,
2) BCM>Reset battery, and then
3) do a BMS reset.

I have done the BMS reset several times before (when changing out the LVB and/or BMS and negative cable), but never the BCM>Reset battery step!
Ford Mustang Mach-E 12v Battery Fault - Service Soon Screen Shot 2022-05-05 at 10.25.26 AM
 
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BillPitman

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I was going to start a thread on this very same issue……!

I am having a very similar issue as @Mach-E VLOG.

I have some observations and questions for the electrical experts AND FoMoCo on here…….
NOTE- car has not been plugged in to charge since midnight of 5/2/22
5/5/22 HVB IS AT 81% SOC……
Observations-
1. I feel some component is drawing excessive current from the LVB, causing 2 different warnings to be shown…..will post those shortly….

I did have this code once-
DTC report
Selected brand: Ford

VIN: 3FMTK3SU1MMA56293
============1==============
B1533(08)
Raw code: 953308
ECU: BCM
Status: Test failed (current drive cycle), Confirmed
Ford: Memory 1 Switch Circuit Short To Battery

2. The HVB is suppose to maintain the LVB when the car is off….. info from manual-
“CHARGING THE 12V BATTERY

Your vehicle has a high voltage to low voltage energy transfer feature that keeps the 12 volt battery charged by the high voltage battery. If the 12 volt battery level is low, the high voltage battery transfers energy to the 12 volt battery when the vehicle is off. “
3. As long as the car is on, the LVB will be charged & maintained as needed

Questions on Warnings I have recently seen……
1. At what LVB SOC%, will the system throw “ system shutdown, to save 12v battery”. Have seen this once 5/2/22 9:09 am ( this tells me the HVB is not maintaining the LVB!)
2. At what LVB SOC%, will the system throw” 12v battery fault, service soon” warning. Have had this warning several times recently, OBD data shows LVB SOC at 42%…… again, why didn’t the HVB kick in to charge LVB.!
3. At what LVB SOC% is the HVB suppose to start charging LVB.?
Hope this tread continues & issues can be resolved……. Bill Pitman
 
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ajbrad71

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When I leave for work it's at 15v and I have a 30 commute. After working 10 hours it drops to 12v and I get a quick pop up 12v fault service soon and then disappears. Doesn't show up on app. Does it every few days. I don't have anything plugged in and just recently got the 21p22 update. Any idea if this is bad or a bug?
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