BMS reset - no tools required

[Farkel]

When you switched your battery, which one did you go with? Did you get a light or fault code or are you doing the reset to be safe. Thank you for your help

I documented this in an old post, but the short version is that I wanted an Odyssey but couldn't get one locally, so I got a DieHard 96R. No lights or codes, but I heard (on this forum) that the reset was needed to let the BMS know when it was dealing with a new battery, so I found those instructions and did it. I also periodically lock it up and let it sit overnight so it can do its self-checking thing.

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[DougS550]

I documented this in an old post, but the short version is that I wanted an Odyssey but couldn't get one locally, so I got a DieHard 96R. No lights or codes, but I heard (on this forum) that the reset was needed to let the BMS know when it was dealing with a new battery, so I found those instructions and did it. I also periodically lock it up and let it sit overnight so it can do its self-checking thing.

Thank. I just asked my Ford dealer Roush Side about that and he said if you don't have a light or code, no need for reset. Now that being said, I will do the rest this week end.

 

[Farkel]

Thank. I just asked my Ford dealer Roush Side about that and he said if you don't have a light or code, no need for reset. Now that being said, I will do the rest this week end.

I'm not going to disagree with an 'expert', but what I read is that the BMS adjusts how/when the alternator kicks in depending on the age of the battery. The reset tells the BMS that the battery is new. Seems like a good idea, since it only takes a few seconds to do. I'll leave your decision to you...

 

[Postal Bob]

The manual for these cars states that when replacing the battery, let it sit indisturbed for 8 hours. The BMS will then reset, and learn the new battery.

After battery replacement, or in some cases after charging the battery with an external charger, the battery management system requires eight hours of vehicle sleep time to relearn the battery state of charge. During this time your vehicle must remain fully locked with the ignition switched off.

 

[Farkel]

The battery charge level monitor will reset on its own. Here's how it's described in the Service Manual "when the battery is charged by connecting the charger to the negative battery terminal, it takes approximately 8 hours for the BCM to learn the new battery state of charge. During this 8 hour period, the vehicle must be undisturbed, with no doors opened or keyless entry button presses"

As for resetting the system when the battery is replaced, it says "If the vehicle battery is replaced, it is very important to perform the BMS Reset using a diagnostic scan tool. If the BMS Reset is not carried out, it holds the old battery parameters and time in service counter in memory. Additionally it tells the system the battery is in an aged state and may limit the Electrical Energy Management system functions."

So, disconnecting the battery probably doesn't do anything relative to resetting the battery life information in the BCM. Otherwise, every time the battery went flat or was disconnected for some reason, the BCM would think it had been replaced, which would make the whole monitoring plan pointless.

BTW, when I described the charging system earlier and used the term BCM/ECU, it's because the BCM is responsible for understanding the battery's condition and the ECU is responsible for managing the alternator output so the battery gets charged properly. They work together to ensure you have an optimally charged battery regardless of age or temperature.

Letting the car sit overnight will allow the BMS to relearn its state of charge. If that's all you want, then a BMS reset isn't necessary.

But that's just one part of the equation.

The BMS also knows the age of the battery and takes it into consideration when choosing the charging strategy. The age counter must be reset when you install a new battery, otherwise the BMS will treat your new battery as if it were old and will charge it accordingly.
I know of instances where some systems (particularly the stop&start, but also the heated steering wheel, or heated windscreen if fitted) had stopped working due to the load shedding caused by a weak battery, and they continued not to work after having the battery replaced. A BMS reset fixed that.

Here's the battery replacement procedure from the service manual.

It doesn't say it's optional. It doesn't say that simply leaving the car parked overnight will do.

If these guys are right, the BMS reset and the 8-hour state-of-charge relearn have different purposes.

 

[Johnnybee]

Just out of curiosity, what all do you lose if you swap the batteries without using one of the memory savers? I’m not really concerned about radio settings, phone pairing or seat memories but don’t want to lose fuel economy or trip info (I’ve never reset trip one so it shows my total run time, which is something beyond 600 hours).

 

[GTP]

I disconnected my battery a couple times while doing front and rear spherical bearing swaps. (I wanted to put the magneride ride height sensors to sleep when they were mechanically unbolted.)

I did not lose my Trip 2 mileage which has been logging since day 1.

 

[ICU812]

Book marked

 

[Johnnybee]

I replaced my OEM with an Energizer 96R AGM yesterday, purchased though Costco Canada. 590 CCA, 45 ah. I did the BMS reset above. No Forscan, so hoping the comment above regarding the car learning the battery type holds true. I then did the routine in the manual. Start engine, allow to idle up to operating temp, idle another minute, then drive 16 km (10 miles). Everything seemed fine. I did fully charge the battery before installing. It has a sliding pull up handle which interferes slightly with the cover, I may just cut it off. Warranty is 5 years full replacement, then stepped prorated out to 100 months. The OEM battery had not failed but I have been checking it off and on and the last time it had dropped to barely over 12 volts. I had started checking it the past winter since it was barely moving, and then a lot of short hops, with the working from home regimen. The specific gravity was low, in the high fair territory. I anticipate returning to the office shortly and just didn’t want to be stuck somewhere. Also lost no settings, other than car reverted to metric measurements for temp and gauges, and I had to choose my gauges for the digital cluster. Radio stations, seat memory, phone stuff, all retained, so that was a plus.

 

[DougS550]

After replacing my battery (with an AGM), I've been trying to avoid paying the dealer for a BMS reset, and I don't have Forscan or even a computer. I found the following on an F150 forum. Tried it on my '20 GT and it seems to work.

Procedure must be carried out within 10 seconds:

1. Switch ignition on (engine off)
2. Pull and release high beam 5 times.
3. Press and release brake pedal 3 times.
4. If successful the battery light will flash 3 times within the next 15 seconds
5. BMS reset completed.

I'm not any kind of expert, but my battery icon flashed three times after performing these steps, so the procedure appears to work. YMMV

Hey, does this procedure really rest the BMS on 2019 GT?

 

[Johnnybee]

Hey, does this procedure really rest the BMS on 2019 GT?

Try it, it either works or it doesn’t, but I imagine it will work.

 

[Farkel]

Hey, does this procedure really rest the BMS on 2019 GT?

I don't have the expertise or the tools that would be needed to see the proof of whether it works. All I know is what I found and posted. Maybe someone with access to the deep dark secret stuff can try it and report what they see...

 

[DougS550]

I don't have the expertise or the tools that would be needed to see the proof of whether it works. All I know is what I found and posted. Maybe someone with access to the deep dark secret stuff can try it and report what they see...
[/QUOTE the reason I ask is, my second battery on my 19 GT which only has 1100 Miles now has two dead cells. When I replaced my original OEM battery last year, The Ford dealership said a BMS reset was not required?

 

[Johnnybee]

If the car sits locked for 8 hours the BMS resets. The procedure just short circuits it. I did this and then did the drive and then the car sat for well over 8 hours so presumably the BMS reset one way or another.

 

[Farkel]

If the car sits locked for 8 hours the BMS resets. The procedure just short circuits it. I did this and then did the drive and then the car sat for well over 8 hours so presumably the BMS reset one way or another.

See post #20

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