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Stop start and battery capacity.


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MK 8 ecoboost 100 2017.

New BCM fitted by Ford dealer. Before that, the stop start was perfect, hot or cold and I really like it (some do, it suits my motoring.) It hasn't worked since. Not once. Tried disconnecting the battery and the BMS reset. No dice. Forscan says the system is enabled and that the battery is a flooded type - yes. it also reports the target battery capacity of 80%. I thought that the stop start needed about 85% so is this a setup error and if so, can I correct it using Forscan to change the target so that the alternator works a bit harder?

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It's odd that's it's never worked after having a BCM fitted. 

Bit of a strange request but it is tried and tested on many vehicles to get stop start to start working again.

Get above 5mph and then stall the vehicle (doing this all in 1st gear should be fine). When it's stalled hopefully you can press the clutch pedal and the car will restart and then the system will work as normal. This may take a few attempts. 

If this still doesn't do the trick try it once or twice more but as it goes to stall press the clutch really quickly to stop it stalling and then give it a go.

Let me know how you get on 👍

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3 hours ago, anon said:

MK 8 ecoboost 100 2017.

New BCM fitted by Ford dealer. Before that, the stop start was perfect, hot or cold and I really like it (some do, it suits my motoring.) It hasn't worked since. Not once. Tried disconnecting the battery and the BMS reset. No dice. Forscan says the system is enabled and that the battery is a flooded type - yes. it also reports the target battery capacity of 80%. I thought that the stop start needed about 85% so is this a setup error and if so, can I correct it using Forscan to change the target so that the alternator works a bit harder?

When you say a new BCM was fitted are you talking about the unit that is part of the Negative battery Lead and if so can I ask why it was changed?

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4 hours ago, anon said:

stop start was perfect, hot or cold and I really like it

Can i ask what it was that you liked stop/start system ?

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1 hour ago, Midgeman said:

When you say a new BCM was fitted are you talking about the unit that is part of the Negative Battery Lead and if so can I ask why it was changed?

the BCM ( Body Control Module ) is located in the interior fuse box ( the one behind the glovebox ) , the one you mentioned which is attached to the negative battery terminal cable that's the the battery monitor sensor ( BMS ).

the BCM is the module responsible for monitoring the battery and it uses the battery monitor sensor input to do so, it controls the auto start stop by a complex algorithm actually.

regarding the issue, I think after a BCM replacement the dealer should have done a recalibration for the battery monitor sensor learned values, without this the auto start stop will behave erratically , battery age and longevity also will be compromised, I suggest you do a relearn for the BMS learned values, I don't know how this can be done technically , but there is a way somehow to tell the BCM the exact battery age so it can adjust the charging and discharging cycles and operate the start stop accordingly.

the dealer should take care of this.

On the other hand you can log into Ford Etis and see if they have done any recalibration for the BCM or BMS or not, every session with their scan tool is registered on Etis.

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Mastertechfix. Thanks but no thanks. Fiesta clutches have a reputation for early failure if abused, so that isn't an option.

Unofix: If you read my post then you will know so I expect that you are trying to pick a fight. That is not why I am here.

Eng. Ahmad: Thank you. That makes a lot of sense. I expect that the correct calibration data has not been extracted from the old BCM memory so the true data has been lost. The new BCM is probably working under the assumption that it is dealing with a new battery, why wouldn't it?

If it means a new battery needs to be fitted to fix it, it is a warranty part as was made very clear to me when I bought the car from a non ford franchised dealer so it will not be a problem but I would prefer to fix it myself if I can and save the environment a battery for a bit. I intend to trickle it up on a smart charger and see if that at least gets the system to the point where it cuts in. If it isn't working at all, it can go back to Ford but if it is, I shall see how long it lasts while monitoring battery voltage.

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  • 3 weeks later...

Ford dealer had the car in to charge the battery last night and had charged it by lunchtime. "The technician walts to run a few more tests, we will call later this afternoon." They didn't so I reckon they are going to do the eight hour reset and relearn procedure overnight before confessing to bafflement. I think it likely that the new BCMI( Body control module i/f) did not get a correct battery time in use value saved when it was installed. The technician reckons there is no such thing. Either way, I expect a new battery will end up being the solution.

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