So I've been running into an issue where the big "Charging System Service Now" my truck, which is a 2017 3.5 ecoboost, and I can't find the cause of the problem. The battery is only from last winter, so just over a year old and I had it tested twice. I've taken the alternator in to get checked, and it came back good. I've even replaced the accessory belt. I've checked the "Alt A" fuse, 38 I believe, as well as the mega(?) fuse that connects to the main alternator cable and confirmed continuity, as well as directly to the alternator itself. I did briefly check voltage on one of the alternator sensor connectors, but wasn't thorough. Each time I've done the BMS reset process, and had the battery hooked up to a slow charger in between. The only thing of concern, is the new battery had a slightly loose connection at times, as the installer used a pin to shim it. I've cleaned the connections, made sure it's tight, and did not see any corrosion anywhere.

My question is, is there something simple I may be missing, either another fuse or the likes? My thoughts are going to an issue with the sensor, the connector to the alternator sensor, an issue on the main harness, or the computer. Or potentially even that the alternator test wasn't thorough enough. Any help would be appreciated, thanks.

 

The 'Charging System Service Now' message appears because the BCM has set a DTC related to a charging problem. The very first thing you should do is scan the BCM for DTCs. Once the code is retreived, someone here should be able to help you.

Use FORScan or a computer based diagnostic tool for the scan. A simple OBD2 code reader will not work for this.

 

Using the OK button on the steering wheel, put it into diagnostic mode without engine running, use up/down arrows and go down to voltage display. 12v or less and your AGM battery is not charged well. Now push accelerator and hold to the floor, crank engine while holding accelerator down, engine will crank but not start, voltage should drop to 10.something on the display, less than that and the battery is weak and not charged, while cranking, release the pedal, engine will start and voltage should display 13.something to 14.something depending upon how much charge the bcm system thinks it needs to charge the battery. If it goes to 14+ volts and never drops down as battery charges, and battery goes below 12 after running and does not stay above 12, then your battery is fuxored.

 

I'll try this tomorrow with FORScan to see what I can pull up, cause yes I pulled with a normal ODB2 scanner and nothing abnormal pulled up while the battery was charged.

And I can try seeing what the computer says compared to the dash, however it seems to hold a charge when I use a slow charger at least.

 

.
I believe you have the early version of the BMS Charging Sensor located >around< the Neg. Battery cable to ground.
Your reader should be able to read one of 3 Codes, P 0620, P 0621, P 0625, or P 0626 or maybe some other code. if there is a charge circuit fault.
If so, look up the description that tells you what the Issue is.
Doing this prevents most of the work and expense you had done.
Good luck.

 

That connection would be my area of focus.

 

So took another look today, it came back with codes P065B and P0625. P065B I think points to the alternator sensor connection being an issue, and I wouldn't be surprised as I work done last year and not sure if that cable got treated well. Other than that, battery came back as expected, and I haven't seen any fuses popped. I was hoping for something nearer the fuse box and battery.

 

.
Code P 065B is charge indicator circuit fault. This fault usually will not affect charging because it's a dash "indicator" driver.
Code P 0625 is low Voltage from Generator Field circuit is too low.
This condition will not charge the Battery.
First, suspect the plugin connector at gen. for fault. Bent pins, plug not fully set in place etc.
Second, wire issue along its length grounded or crossed.
Good luck.