charging problem

[Jetsmoke]

I have a 2007 Sierra. I have noticed that the voltage fluctuates between 12-14 V. Sometimes it charges at full then will slowly drop off to 12V. Or sometimes I start it up and it doesn't charge at all. So I took the alternator off to have it tested at a few of the local parts stores. None of them had the correct wiring to test it. So i figured I would just bite the bullit and buy a replacement alternator. Since I thought the problem was the voltage regulator which is a component of the alternator. But the new alternator is doing the same thing. Is something else controlling the voltage output?

How amy others have this problem?

 

[Z15]

You do not have any problem. That's the way the new alternators work. The only charge enough to get the job done and when they are not needed they go into economy mode. It explains it in your owners manual.

While the engine is running, this gage shows the
condition of the charging system. The gage
may transition from a higher to lower or a lower to
higher reading. This is normal. Readings
between the low and high warning zones indicate
the normal operating range. The voltmeter
gage may also read lower when in fuel economy
mode. This is normal.

 

[Jetsmoke]

Wow that is a good idea. Too bad I didn't research more before buying a new one. I just bought the truck a couple months ago and I guess I'm used to seeing the traditional 14 V constant on the gauge. Any variation from that made me think something was wrong. Thanks for your help.