Voltage seems low at idle

[Daniel_B]

Hello I have a 2011 Silverado with the 5.3. I was sitting in a parking lot today with the air conditioning all the way on and I noticed my voltage guage seemed low. It would stay low like seen in the picture for a while and then the alternator would kick in and bring it back up. Then it would drop back down and repeat. Seems fine while driving. Here is a picture of the lowest it got

[Supreme Pizza]

Many newer trucks automatically turn the alternator off and on automatically to save fuel. Either that, or you have a failing alternator or voltage regulator.

[swathdiver]

The BCM will throw codes if lower than 12.4 volts the ECM wants no less than 11 volts or it will throw codes.  That looks like 13 or high 12s.  If your battery was fully charged the alternator will cycle off which is what it was probably doing there.  

 

Look up EPM, electrical power management and RVC, regulated voltage control to learn how this works and what to expect.  Pretty cool stuff.  You can easily disable it by disconnecting the 3-wire connector that goes around the battery current sensor which is right off the battery on the negative cable.  Then it charges all the time at 13.6 volts if memory serves.

 

I've grown to like it, it helps the batteries live a lot longer.

[MaverickZ71]

On your temp, oil pressure, and voltage gages, you'll notice hash marks at roughly 10 o'clock and 2 o'clock.  Anything between those marks is normal operating range.  Anything outside that range, and you'll get a malfunction message in the Driver Info Center screen.