Low voltage issue?? Help

[Chaos150]

For the past 2 days after about 15 to 20 minutes of driving I start getting a whole bunch of warning messages. Lane assist. Hill decent. Etc. are out of service. Service vehicle soon with the little wrench appears. They pop up and go away and eventually stay. I checked my battery this morning with a little battery charger and it said it had 12.3 volts and was at 50% capacity. Left it to charge for about 20 minutes. Drove the truck around town and the messages came back again. Got home and checked the battery. It was 12.4 volts 70% capacity. Anyone every run into this before?? Truck is 21 3.5 ecoboost by the way

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[Porpoise Hork]

How old is your battery? An aging battery or BMS that has not been reset for close to 3 years can cause all sorts of issues like this.

Motocrap batteries rarely last past 2-3 years (mine died at 14 months). If your truck is more than a couple years old and have not done so then seriously consider replacing it with a new H7 (for PowerBoost) or an H8 (non PowerBoost). The H8 will fit but it will be snug and you may need to get a different battery blanket. Walmart batteries are much cheaper than parts houses and last just as long if not longer. Once you replace it perform a reset on the BMS and put the battery on charge for at least 4 hours or till the main charge cycle completes to bring it to 100% making sure to place the negative connecter to a body ground so the BMS can see the charge current entering the battery so it will properly update. After you have charged the new battery it may take up to 8-12 hours with the key off for the BMS to accurately update and report the correct state of charge.

You can also use Forscan to increase the default SOC setting from Ford's 80% to 95-100%.

 

[Gros Ventre]

The system voltage is set by the truck's computer. Unlike older systems where the voltage regulator in the alternator matched voltage to a lead acid battery's characteristic. Then you have an AGM Battery. It's still lead acid but requires some different care & feeding. Ford has set the "fully charged" voltage at 80% or 12.8 VDC. At the end of the day, I have concluded that Ford Batteries are defective in some small way. Four months after delivery I began receiving warnings about the electrical system while on the highway at 65. Hm-m-m... Shortly after was on my way to family Thanksgiving dinners. Stopped into a nearby NAPA store and purchased and installed a catalog, off-the-shelf AGM battery. Turned out to be an H-7. When travels were over a few days later, put the new battery on a "wetting down" charge. It went 10 hours to completion. Have not had a peep out of the system since, 3 years now. It's gone through 3 Wyoming winters so far no sweat. Later took the OEM Battery into the dealers and they tested it. Came up fine. Go figure, but I'll not buy a Ford battery in the future. My thought is: Just go split for a good, non-Ford battery and be done with it.

 

[Chaos150]

I bought the new battery back in August of 2023 so it should still be under warranty. I’ll probably take it back to autozone for a warranty replacement and try it out.

 

[Porpoise Hork]

I bought the new battery back in August of 2023 so it should still be under warranty. I’ll probably take it back to autozone for a warranty replacement and try it out.

When you replaced it did you reset the BMS? If not then do that and put it on charge until the charger completes the cycle. Just be sure to connect the negative to a body ground.

The reason for the reset is the BMS has logic in it that estimates the battery's reserve based on age. Over time this decreases as the battery ages. and the BMS will start powering down various modules to preserve the battery health when the truck is shut off. It'll do this even if you replace the battery but don't reset the BMS. I have also seen the BMS start doing this on a 2 year old battery that tests good and resetting it and letting it sit overnight to update the SOC resolves most of the weird issues. Now if the battery is heavily degraded due to being kept at a low SOC for prolonged period of time you can try running a good 12 hour desulfation cycle with an AGM charger that supports it to see if it will restore some of this life back, but may still end up having to replace it.

 

[Chaos150]

No I never did do a BMS reset when I replaced the battery. I’ll do that here in a bit. It’s on a battery tender right now

 

[Gros Ventre]

A BMS reset is good practice... That said when I replaced my battery I just put it in and drove, later doing the wetting down charge. Again not then smart enough to put the negative charger cable where I should have. The key is the system will figure it out in a few days to a week, as mine did.

 

[Porpoise Hork]

No I never did do a BMS reset when I replaced the battery. I’ll do that here in a bit. It’s on a battery tender right now

When you do the reset and take it off the charger it will likely report a low SOC. Stupid thing needs some 8-12 hours of key off to properly detect and update the SOC. Some genius engineer decided that the trucks needed a super flaky and complicated charging system instead of a god old standard alternator that accomplished the task perfectly for 50+ years...

 

[Chaos150]

Did the reset and tried to start the truck. All kinds of warning messages came up. Coolant temp and oil temp. And the truck won’t even start. Everything else comes on but no start

Put the charger on it and it started. Thank god lol I was ready to perform surgery and take this battery out. With it running. All these random messages are popping up still. Park aid. Blind spot. Coolant temp. Oil temp. Pre collision assist. Turned the truck and going to let it keep charging.

 

[Porpoise Hork]

Wonder if your BMS is having issues or that your battery is just really weak. If you're going to let the truck's alternator handing it for a bit, be sure to leave the fob in it and hvac blower on 5 so it will crank the voltage to 14.2+. Otherwise it'll hover around 12.8-12.9v.

 

[Chaos150]

I’ll probably just replace it when my wife gets home. That way I don’t have to deal with all these headaches

 

[Chaos150]

Alright guys here’s an update. I did the BMS reset yesterday. Ran some errands. Picked up the little one. Drove around for about 20-30 min. No messages. Badass right. Well today as I was driving home boom messages came back. Said F it bought a new battery put it in did the reset. Let the truck idle so I could put away the Camaro. Get back in the truck. Guess what. All those messages appear while idling. I’m out of options.

 

[Micho523]

Scan for codes with Forscan. Go from there.

 

[JohnTrigger]

Messages can sometimes take up to three key cycles to disappear. Hoping that’s it.

A person or two has had squirrel or rat eat through wires causing weird electrical short issues .

Maybe your ground wire is bad-trace it from the negative pigtail to chassis.

Reseat all you under hood fuses in fuse box, several people have had a few of them loose.

 

[Porpoise Hork]

@Chaos150 I did some digging into Ford's BMS since I have been having some odd quirks myself and found out that Ford has made multiple revisions the sensor at the negative terminal over the past few years. The older variants would sometimes under-report the actual SOC and cause various low 12v warnings, modules to be forced into deep sleep, unexpected HV battery drain when parked. All symptoms mine has exhibited at one time or another even after ensuring all 12v batteries were fully charged.

The superseded part number is ML3Z-10C679-B that is supposed to resolve these problems. The part number is printed on the top of the BMS and if it's not the one listed then it may be the root cause of your warnings and odd reported voltage behavior. And if it does match you may have a faulty one. I just ordered one of these since it's only $20. and will be swapping mine out in a few days to see if it resolves the off charging and random HV drain issues mine has had.

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