Mach E HVB SOC Drop Issue

[gloverpnw]

Hi Folks,

I'm having an issue with my brand new 2024 Mustang Mach E Premium AWD Ext. Battery. Whenever I leave the car unplugged for a couple hours, I see a huge drop in HVB SOC (see attached). I did a test this weekend to confirm. Right after charging my car to 90% (parked in attached garage), I unplugged it and measured the SOC, then waited almost 24 hrs later (car completely off) and measured again. I'm seeing about a 10% HVB SOC drop and almost a 10kWh drop. HVB SOC Display stays the same until I start the car, then quickly starts dropping. Currently using the Ford charger at 110V while i'm awaiting a level 2 charger install in about a week.

Has anyone seen this issue? In any world is this normal or part of expected operation?

Thanks

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[AliRafiee]

I’ve never actually done this test. But that seems really odd. I wouldn’t expect any significant drop in HVB.

Are you accidentally hit the remote start button a few times during the day?

 

[AKgrampy]

I do not mess around with taking readings much but my guess is those two readings are erroneous. Does your vehicle displayed SOC drop all the way to the lower value? Essentially there is no way for energy to just disappear.

 

[Snakebitten]

So the displayed SOC stayed the same, yet the actual SOC changed 10%.
And the battery temperature was basically the same for both readings.

That's definitely odd.

 

[Mach-Lee]

The battery voltage is basically the same, so it’s not actually draining. This is some weird BMS issue. It may be Level 1 charging makes things more difficult for the BMS due to the low currents involved. The extended pack should be around 380V at 90% charge, it's much lower than that (368V) so charging to 90% is being terminated early.

Can you charge the battery to 100% (on a Level 2 if possible), let it sit 5 hours, and see if it still happens? Note: Because the BMS is off, it may take an additional 10 hours longer than the estimated completion ETA for it to actually finish charging at 100%. Drive it and see how far the SoC drops in the first minute or two.

Also since you have car scanner, can you take a look at the cell voltage and cell capacity variation parameters?

To be safe, I'd recommend you bring it to a dealer so they can do a battery health scan on the pack and verify you don't have a failing cell. There is a similar SSM out for the F-150 Lightning:

SSM 53208 2022-2023 F-150 Lightning - Reduced Driving Range Projection And HV Battery Pack SOC - Unable To Reach Target SOC Using The Scheduled Charging Feature - No DTCs In The BECM

Some 2022-2023 F-150 Lightning vehicles may exhibit a reduced distance to empty (DTE) projection, a high voltage (HV) battery pack state of charge (SOC) that drops from 100% to less than 90% within 60 seconds of being driven, and an inability to reach a target SOC using the scheduled charging feature without any diagnostic trouble codes (DTCs) in the battery energy control module (BECM). This may be due to an issue in one or more cells within the HV battery pack. To correct the condition, run the "BECM Battery Health" application using the latest software version of the Ford Diagnosis and Repair System (FDRS). If any cells are identified as exceeding state of charge and/or capacity thresholds, refer to the Workshop Manual (WSM), Section 414-03A High Voltage Battery, Mounting and Cables > Diagnosis and Testing > High Voltage Battery, Mounting and Cables - Electric > Pinpoint Test AP > Step AP4 and continue diagnosis. If all cells are within state of charge and capacity thresholds or DTCs are present in the BECM, refer to the WSM for normal diagnosis. For claiming, use causal part 10D672 and applicable labor operations in Section 10 of the Service Labor Time Standards (SLTS) Manual.

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