2003 Dodge Dakota 4.7 motor. The volt meter dropped all the way to the left side of the meter. I was driving the truck the check the gages light came on. I looked the volt meter was not on. I had the battery and altenator check at Autozone and O'Reily and both past. I drove the truck home and the volt meter started working. It worked for 2 weeks until it came on again. I was a good ways from the house that it came on. I tried to get back home but the truck shut down. All the lights flashed and then there was no lights at all.I had the truck towed home. I changed the battery out with a new one. The truck started and ran for awhile but then the check the gages on again and the the volt meter was not on again. The altenator checked again and still putting out 13 amps. All the connections on the battery,ground connection on truck frame, and the postive connections are all clean.I don't know what is causing having low voltage. Other than the low voltage the truck runs fine.

 

The PCM controls the alternator output based on system voltage and battery temperature. You might look at the battery temperature sensor, although I would think there would be a code for that. It can turn the alternator all the way off, or make it run at 100% output whenever it wants for pretty much any reason.

 

Sounds like a ground issue. Mine needed all the grounds traced and cleaned and mounting points cleaned

 

Take the alternator out of the truck, then have it checked. I had some issues and an auto parts store checked the alternator while in car and told me it was good. I pulled it out and checked it at another parts store and it was bad, truly bad.