Hi all, I've Googled for a week and found related threads, but no conclusive answer to this issue:

The original battery on my 2017 3.5 EcoBoost was getting low for a few weeks. The Auto Start-Stop no longer worked. Starting the truck was sluggish. A trickle charger kept it going for a little while, but it was time to replace the battery. I bought an Interstate H6 AGM battery at Costco, and as anticipated, the Auto Start-Stop resumed working after about 24 hours. It seemed everything was normal for about two weeks.

One day, I got in the truck and tried to start it and it didn't turn over. I had power (gauges, radio, remote entry, etc), but the truck wouldn't turn over. No clicking. Just nothing. I turned the key off and then tried again immediately and it fired right up like normal. This happened two or three more times. The rest of the time, it started like normal.

Then, on three different occasions, at a stoplight, the Auto-Stop worked, but the Auto-START didn't. We got a message on the dash that said "Auto StartStop Manual Restart Required." Then it wouldn't start for a few panicked seconds.

I got online and read about the BSM reset and did that whole thing (five times headlights, three times brake, etc). It didn't change the behavior. So I tried it again, but I still got the occasional no turn over. I read another article that said to disconnect the battery, touch the cables together for 60 seconds, leave the truck disconnected for 30 minutes, then replace the cables positive first. I tried starting it afterward and no turn over. Tried again and it started right up.

I took the truck to the dealer for an oil change and asked them to check the BSM. Everything came back fine on their diagnostic (which makes me wonder if they really did one). As soon as I got back in the truck, I got the same issue.

I don't want the dealership to start chasing issues at my expense. None of these issues happened until I changed the battery. Does this issue sound familiar to anyone? Any input would be greatly appreciated. Thank you!

 

Unplug the BMS plug at the negative battery terminal. Your battery will thank you as it will now be allowed to charge past the 80% threshold and the regulator can finally do its job unencumbered.
I've had my 2018 unplugged for the last 6 years / 124K miles without issue. A bonus to this is that the idiotic start/stop feature goes away as well.

 

Thanks for that. I don't mind the start/stop feature, but the idea of being able to charge past the 80% threshold is nice. I wonder if this addresses my issue of the truck not starting from time to time, though? I don't think it's a low battery issue.

 

Unplug the BMS and take it for a good 30 minute (or more) drive to charge the battery. Then give it a week or 2 and see if the issue has gone away. If so, then plug the BMS back in and see if issue returns.

 

The BMS does not prevent your battery from being charged above 80% SOC. The BMS uses something Ford calls SRC (Smart Regen Charging). The "SRC will conserve fuel when the battery is in the 80% range by lowering the charging system voltage which reduces alternator torque on the engine" - Reference Ford GSB V2 Battery Charging & Testing.

SRC reduces the charge voltage but does not eliminate it. The battery will continue to be charged, just a a slower rate. This is the same as all smart chargers which reduce the charge rate as the battery nears full charge. The reduced charge rate lets the battery cool allowing it to accept more charge.

Your stating issues are not related to the BMS. You have a wiring or starter issue. Check all your grounds and power cables running from the battery. Don't forget to check the connections in the High Current BJB. There is also a weak spot in the starter design. There is a copper cable which connects the starter solenoid to the starter. This cable is open to the environment and can get corroded and cause starting issues. You need to check that as well as it can cause intermittent starting problems until it fails completely.

 

I've had 3 trucks go over 100K miles with the BMS unplugged with zero charging issues.
There are lots of F150 owners out there that plug their truck battery in at night to a battery maintainer to deal with the problems created by the BMS when it gets out of parameter. The BMS creates more problems than it fixes. Oh wait, it doesn't fix anything.

 

This is 2024, leave the BMS working as designed. Was the battery ever fully charged after you bought it?

 

Update: After creating this thread, it took two tries for the truck to start so I could drive to an appointment across town. But when I finished the appointment, the truck wouldn't start at all. I tried many times and got nothing. Just one click. Stranded! I finally called a friend who came with jumper cables, but it still wouldn't start. Then a message came up on the screen that said "Charging System Service Now." I tried one last time before calling a tow truck and PRESTO, it fired right up.

I brought the truck home and checked voltage with my multimeter: It's reading 12.70 volts when sitting, 14.35 volts when running. And it starts right up...for now....

 

How old is your battery? Sounds like you may need a new one. These trucks are very finicky when a battery is less than 100%. Interstate is unfortunately not what they use to be.
Check the connections at the battery to be tight and in good condition.

 

52 Merc has all the correct diagnosis.
Said another way, Charging and not cranking are two different issues.
Granted, if the Battery is not up, cranking will be affected.
But cranking control is from a different location and uses direct connection to the Battery.
If (that part of the circuit) has a fault there will be cranking issues whether the Battery charge is up or not.
Leave the BMS plugged up. Removing it will not have any possible fix for a >starter circuit< failure.

The biggest issue of low voltage failure is the Battery high Current drain capacity for Cranking is different than the Low Drain Capacity of the Battery and gets lower with age..
The two are not a Linear relationship, therefore a Battery can crank the engine but fail to hold light load voltage level Drain capacity while sitting etc.
This causes many to try work arounds when it's a reduced low Drain Capacity issue. Its just the way batteries with chemical derived cell power are, and age.
The BMS system is an attempt to optimize Battery life from these inherent Battery application issues by using Temp, age, cell health, charge level controls and delayed charging from the Alternator when conditions change.
As the Battery ages, these capacities reduce but not all at the same rate in each Cell.
For example, when cranking, the Alternator is shut off to reduce load on the engine, then is turned on at a lower level that gradually rises to the charge level the Battery will take and provide Current for the rest of the vehicle needs. All done from the BMS system. This is why you don't the disconnect the Sensor at the Battery.
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Good luck.