[05z71]

hello, i just purchased a 05 avalanche Z71, everything was fine untill i was driving at night when i noticed the voltage guage was going from 12.5 to around 15 or 16 volts, all my lights were dimming and getting brighter, i took it back to the dealer and they tested the alternator which they said was good and producing 84 amps of current, then they had the battery on charge all day and that tested good. i'm no stranger to vehicles and electrical so after i picked the truck up and it started doing it again, so i checked the output of the alternator with my multimeter and i was getting a reading between 13.6-13.9 volts (always changing) with a few spikes of 15.5volts. i'm looking mainly for second opinions befor i head to the dealer in the morning but to me it sounds like the regulator in the alternator is shot...just a lil extra info, the alternator is a 140 AMP unit.

 

[Gmcsuvguy]

If the shop load tested your alternator it should have been putting out the rated 140amps, to me it sounds like you have a regulator problem.

 

[05z71]

well..i went for a second opinion, this time to a different GM dealership, they said the alternator is good, but the battery was toast...so i replaced the battery....but the volt guage has eben see creeping up around 15-16 volts but only for a breif moment....is that normal? the dealership is trying to tell me that you'll see if go up like that when the vehicle needs a little extra power (ie - air conditioning turns on) i always thought that cars ran off 12.5 volts and charged at 14.5 volts