Debugging "12-Volt Battery Charging System Malfunction", 3rd Gen (2022) Advice

Hello - As I wait for the 'earliest available appointment' at a nearby dealership (in two weeks), I am hoping to get advice on debugging this new 'charging system malfunction' dash message in my 3rd gen. What else would you try or suggest while I wait for, probably, a new alternator?


Background:
2022 limited, 4wd, 5300 miles, no mods of any kind, no new window tint (just factory, a few places have said apparently liquid from tinting can cause this issue but it resolves when it dries out). A few days ago the dash message came on. Obviously well out of warranty, have not done the motor swap yet, but have done all over available recalls.

Error Message:


Replacement parts:
- I needed a new passenger side tail light, I accidentally bought a 3 pin instead of a 5 pin. It worked if I wasn't applying the brake. Ran that for about a month while i waited for the correct 5 pin to arrive.
- I replaced the passenger side mirror pvm camera, OG one decided it had enough and ejected itself in a strong headwind on the highway. Replaced with a broken mirror but the camera trim/camera looked ok off ebay that had that part (instead of toyotas solution me spending $1200 on a whole new mirror)

What I have looked into:
Battery at rest sits at about 12.5/12.6 volts
Battery while truck running about 12.2 volts, slowly dropping

Tested every fuse (not in fuselinks) across all three fuse boxes, and were all ok
Tested every charging system/starter relay (all ok)
Didn't go through the fusible link removal ordeal to check, but through the window/what i can see they look un-popped.
Unhooked battery for an hour hoping to re-set the computer to see if it would see the issue again. Unhooking battery didn't seem to change anything at all with the truck.
Ran code scanner before and after - no codes.

Thank you for reading my long message.

 

Sounds like a bad alternator...

 

Ha, yea, i was hoping there was more things that I may have missed that i could try to save me the 2 or 3 weeks worth of daycare costs this repair is going to run. I thought, 'maybe i can do this myself' until i saw where the alternator was.

 

For anyone wondering, 3rd party toyota certified shop, front range colorado, summer 2025

alternator diagnostics: $105,
quote for new alternator: $2300 ($550 for part, rest for labor and other shop fees)

 

I got a call from toyota the new motor was ready to install same day I got the quote for the dead alternator.

Third party shop cleared a code that my odb2 scanner could not see. Was charging fine after clearing the code.

I had it towed to toyota to do the engine swap, do their own diagnosis for $200, so that way if the alternator was bad they could just swap it when doing the motor swap - they said the alternator was fine while doing the motor swap, but that the truck didn't have the right battery, that was causing things like auto start/stop to not work.

So the final outcome is:

Truck has gremlins or something.

 

Maybe the voltage regulator is the culprit? Miles are pretty low on the truck. Battery could be shot as well?

 

Thank you for the tips. Turns out, when i got the truck used a while back the OG owner replaced the battery, and it was causing various peripherals to not work right for still unknown reasons. Going to a toyota battery the alternator works fine, android auto works wirelessly again no problem. Other random gremlins seem fine as well. Weird and I never would have caught it.