iv got a 08 gmc serria 1500 with the 5.3l whith avtive fuel magagment.
i noticed this morning when i went to the bank that the battery gauge said 12 volts so i stoped in the parking lot and shut off the engine and started it back up and it said 14.5 volts so i thought it was ok so i watched it as i went back to home and it slowly fell back to 12 volts again im thinking the alternator is failing this truck had 600 miles on it and this seems to be too soon for this problem what do yall think iv got an appointment at the dealer wesenday to get a bedliner put in so i thought id ask them

Chris
your truck has a battery module on it if it does not see a need for full charge it drops the pulse with modulation to the altenator exciter and thus the voltage drops,i would not worry to much unless it sets a check engine light.It will vary the voltage as needed,also if you were to put a meter on the battery you would probably find that it was actually charging at about 12.9 volts,the cluster is always lower than the actual charge getting to the battery.

oh ok so its a new way to keep the altnerator from over charging the battery cool thanks stan

It's a cleaver way of turning off the alternator thus reducing engine load & improving economy.

yea ok but shouldnt it read normal when there is a load on the battery and why is the windows slow going up

It's the alternator. Mine did it also, same truck but an 06'
The computer will shut down certain things to conserve the battery to run more important things.... or something like that. First it started with the windows and then the door locks.

yea its confirmed i put my diagnostic meter on it and drove it it starts out at 14.8 volts and drops to 11.8 and it necer rises when i put a load on the syster even with all the lights fans wipers a/c and the 2 coolong fans in front of the rad come on it never moves just those 2 rad fans is alot of current looks like gm will be fixen it