i have a 2007 chevy uplander 3.9 motor it gave a charging failure on display wouldnt go over 12 volts i cleaned battery posts got in it 8 hrs later it was running 14.5 volts drove to store got in car faulted again driving home went to 12.5 volts shut it off started back up and it was at 14 volts any ideas what it could be

Unfortunately, you need a scan tool, like a GM Tech II scan tool, to really diagnose this system, since the alternator is regulated by the ECM, and also uses input from a current sensor that goes to the BCM......

So you need a scan tool like a Tech II, to scan for not just P codes, but also U and B codes, that might point you in the right direction.....

This not like old systems where the regulator was built into the alternator, and sensed system voltage on it'* own.....in this case the ECM controls it....

So potential problems are ECM, BCM, current sensor, alternator, or a possible wiring problem....

It would seem that the Uplander has a host of charging related problems.
Feel free to start @ page one, but I am posting page 3 as the last post has a comprehensive check list.
Charging System Failure Mystery | Page 3 | Green Flag Auto Forum