Just for giggles, we have an 06 Mondeo with a heated windscreen. Works every time. Lol! 

On 1/15/2021 at 10:03 PM, Waggy said:

Don't get a new battery until you've tried resetting the BMS. Plenty of recent threads.

So with a bit of spare time on Sunday and having read up on the BMS reset procedure I decided to give it a go as £400 to the dealers still isn't sounding attractive.

Anyway, I reset it and noticed I was getting the greyed out stop/start icon on the dash.  It was only 1/2deg outisde so not sure if this was battery/BMS or ambient temperature related.  I'm not too worried about this at the moment and will see what happens with this when the  weather is forecast to warm up later this week.  If it continues then I may well end up putting a new battery in as I'm on the original one and it's coming up 5.5 years old.

Now, leaving the car overnight to freeze up I got in it this morning and did the BMS reset again for good measure and am happy to report that my front windscreen defrosted (tested with just the windscreen heater on, no AC blowing).  I am hoping it freezes again tonight so that I can test it again in the morning and see if the states held in the BMS this morning have been remembered?

So results are in... Gotta say I don't really blame the dealer for any of this, they do seem to be trying their best.

Firstly the heated front windscreen didn't work because the battery charge was too low. Not much of a surprise there.

Secondly the BMS was reading the correct battery state as they tested it with a standalone battery monitor. So the BMS knew the charge was low...

Thirdly there was an update to the system that included the BMS so the dealer is hoping that this, together with a battery charge up and a BMS reset solves the problem...

But talking with one of the tech guys, he described how the emissions targets and fuel efficiency demands mean that the alternator and BMS no longer charge up the battery like they used to. They're tuned to replace just the charge taken up in running the car. This seems like madness to me, but the conclusion was that I may need to give the battery a boost by trickle charging it every winter if this problem persists...

 

That is very interesting but the madness is that the very time that you want your heated screen to work is in the winter, when the battery is less efficient due to the low temperature as it is a chemical reaction that slows down as the temperature drops. My wife has a Fiesta without the fancy BMS and the heated screen works whatever the temperature. It feels wrong having to scrape the screen on a modern sophisticated vehicle that has a screen heater that you cannot use in the winter unless you put the battery on external charge - that is something I used to do when my cars had dynamos. Ford should build in a BMS override, either auto or manual, such that the Heated screen is allowed to work when it is cold.

19 hours ago, Paulius55 said:

Ford should build in a BMS override, either auto or manual, such that the Heated screen is allowed to work when it is cold.

I completely agree with this. There should also be an option to pump the battery full of charge, fuel efficiency be damned. If I know I want to take the car on a short journey with all the electrics on, it would be great to maximise the battery charging on the way.

Hi, newbie here, just to add my experience to the discussion.

I have a 65 plate S Max with a failed heated windscreen. Having read this excellent thread I used Forscan to reset the BMS. Before the reset I looked up the battery parameters. The battery charge percentage (BAT_ST_CHRG, %) was 64% and the battery age was the age of the car.

Having run the BMS reset programme the only parameter I could see that had changed value was the battery age had reset to 0, battery charge still at 64%.

Quick check of the heated windscreen and hey presto it worked.

So does the BMS algorithm for load shedding consider an old battery as not suitable for windscreen heating / start stop / etc? Very strange if so.

Anyway thanks for your collective knowledge, I will let you know if it continues to work or not.   

  

On 2/10/2021 at 11:45 AM, Merlin16 said:

Hi, newbie here, just to add my experience to the discussion.

I have a 65 plate S Max with a failed heated windscreen. Having read this excellent thread I used Forscan to reset the BMS. Before the reset I looked up the battery parameters. The battery charge percentage (BAT_ST_CHRG, %) was 64% and the battery age was the age of the car.

Having run the BMS reset programme the only parameter I could see that had changed value was the battery age had reset to 0, battery charge still at 64%.

Quick check of the heated windscreen and hey presto it worked.

So does the BMS algorithm for load shedding consider an old battery as not suitable for windscreen heating / start stop / etc? Very strange if so.

Anyway thanks for your collective knowledge, I will let you know if it continues to work or not.   

  

Good to hear. Had your troubles started since the recall to fit the fused loom on the monitoring sensor?

I had similar problems with my 18 plate S max. It went in for the fused link last June and this winter the screen didn't work. Come to think of it the stop/start hadn't worked for a while but I never noticed. It went back to the dealer under warranty and noting showed up as nothing wrong, the even kept it overnight and it froze hard and the next morning it worked. Absolute bol***s. the next two mornings it froze and it still didn't work so I tried the BMS reset, 5x press rear foglight then 3x hazard warning. Nowt, nix nothing so I left it. Some time later, reading a FocusRS blog, someone tried sequence ignition on, 5xflash high beam then 3x press brake pedal, and it worked, the battery light flashes 3 times. I noticed that the stop/start began working again and on two recent occasions the windscreen demisted within two minutes of starting and without any blow. I told the dealer and for once they were very interested and logged the information in the workshop notes. Logic would suggest that when you reset the BMS, even if the battery is at 90% of the original power, the new BMS reading will keep the HFS and the stop/start working until power drops to less than 80% of this new reading. Hope this is some use to you guys 

I reported this to Ford UK recently who replied saying they are aware and looking in to it....

Hi. Any further update on this. Mine also started after the recall ? 

Mines is working great. Only took a 340 mile round trip, to charge the battery sufficiently.  🙄

I have 66 plate Galaxy that has a heated windscreen that never worked, was also told by Ford engineers it was the battery voltage that was the issue. The original windscreen was replace recently after getting smash by a stone, auto glass technician advised there was no power going to the screen when they did their checks… I then checked both the 40amp fuses in the engine bay fuse box, they were fine. I then stumbled across an article about  resetting the Battery Management System (BMS) which you are supposed to do when your replace battery, but the manual makes no reference of this fact.  Instead after a long journey in the car with the battery voltage at 12.5 I performed the BMS reset. 1. Press the start stop button 

2.flash high beam 5x times

3. press break peddle 3 times

4. watch for the battery light flashing on off three time

5. Start the car, let it run to build charge in the battery.

6. Turn on the heated screen

The heated screen started working, I could not believe it, after 7 years of ownership I now have a working heated windscreen !!

Also, the message on the central screen that used to flash up “Switching system off to save battery” also stopped appearing. I also expected but have not tested yet, that the auto start stop will begin working again.

So, the Ford engineers where half right, shame they didn’t mention the BMS reset though ?!

 

 

On 11/26/2023 at 3:41 PM, unofix said:

There are a couple of things that have to be met before the heated front screens (there are two separate half's) will operate.

Firstly the State Of Charge of the battery must be at least 70% or better.

Secondly the outside ambient temperature must be 7^oC or less 

 

So I thought it was generally not recommended to do BMS reset?

I had this issue last year and used a maypole charger to top battery up and it started working. 

Going to put battery on charge tonight and leave until Monday morning. 

Should I still do BMS reset? 

2 minutes ago, DaSingh said:

Should I still do BMS reset? 

NO !! 👍

Only reset the BMS system if the battery has been replaced with a new one. In all other cases the BMS system will adjust/correct itself in 24 to 48 hours even if the battery charging procedure has been done incorrectly.

Resetting the BMS deletes the battery age and it's characteristic charging algorithm. This will sometimes cause Stop/Start to work again (God only knows why anyone would what that) because the BMS has to assume the battery is fully charged. After a day or two the BMS will recalculate the batteries State Of Charge and if low it will once again disable Stop/Start. Of course the BMS can't correct the age once that has been deleted and so the Smart charging system will continue to charge the battery as if it was new. This could possibly reduce the lifespan of the battery.  

3 hours ago, unofix said:

NO !! 👍

Only reset the BMS system if the battery has been replaced with a new one. In all other cases the BMS system will adjust/correct itself in 24 to 48 hours even if the battery charging procedure has been done incorrectly.

Resetting the BMS deletes the battery age and it's characteristic charging algorithm. This will sometimes cause Stop/Start to work again (God only knows why anyone would what that) because the BMS has to assume the battery is fully charged. After a day or two the BMS will recalculate the batteries State Of Charge and if low it will once again disable Stop/Start. Of course the BMS can't correct the age once that has been deleted and so the Smart charging system will continue to charge the battery as if it was new. This could possibly reduce the lifespan of the battery.  

Exactly what I thought. Seems some people are just going ahead and resetting. 

My battery going to recharge over the weekend so should be good by Monday.