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Focus MK4 “System off to save battery” and app errors

captaincadet
captaincadet
in Ford Focus Club

Featured Replies

On 9/7/2025 at 11:01 AM, captaincadet said:

Only concern I have with that was when the garage did it, it ended up having to be taken to Ford for a reprogramming job as it lost all its settings. 
they didn’t ask Ford to do a battery diagnostics though…

Hello there,

With the new battery you are seeing what I would have expected. I have had exactly the bad battery simptoms you described, and also like you I wanted to know for sure it was the battery, before paying for a new one. And indeed it was.

 

Now, the question I have is about the car needing reprogramming. I have never heard that before. I removed my battery several times and nothing happened. The car would just reestimate the battery's state of charge and everything would be operational again. Furthermore, my background is in the automotive industry and there is no such thing as ECUs needing reprogramming because their power was cutoff! What does happen is that the ecus' non volatile memory is not written properly, but the firmware running on the ecus can cope with that. At least for the ones I have worked with. I could imagine there is a bug somewhere in the software and that could mess up something, but i can't imagine the car not being able to handle a battery disconnection on purpose.

  • Quote


    The car handles the battery being disconnected. When you fit a new battery the BMS system should be reset so that it knows that a new battery has been fitted. Don't reset the BMS if you have just disconnected the old battery and reconnected it or if you have just recharged the old battery. 

    The BMS stores the battery age as well as it's state of charge. The battery age may be used to set a charging profile in the smart charging system.

  • Quote
    • Like 3

    BMS reset only when a 'new' battery has been fitted.

    On 3/29/2023 at 8:14 PM, unofix said:

    How to reset the BMS method 2                                                                         Search Tag: BMS2

    CAUTION: The reference at the beginning of the video saying that the BMS should be reset after charging the battery in incorrect.

    The Battery Monitoring System (BMS) should only be reset if a new battery has been fitted.

     

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    The "Digestive"

    • The Digestive Forum Roundup (24th May - 31st May 2026)

      Steve ·
      The Digestive Forum Roundup (24th May - 31st May 2026) We hope this email finds you well and enjoying your week. As always, our forum has been buzzing with activity, so we’ve compiled the highlights for you. Plenty of interesting discussions are taking place, especially around the Ford Focus and Fiesta models. Starting off with the Focus, many members have been discussing issues with the Emergency Call System, particularly in the Mk4 model. PLB raised concerns about persistent malfunctions, a se
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