I have noticed that when I first start my truck the VLT readingon the scangaugeII is at 11.8 and stays that way for about a minute. Then thereading goes to 14 vlts with no change in RPM’s or gear. The factory gauge doesnot change and shows normal; there are no codes or any warning lights on.
My truck has the dual Alternator setup, do you think themain alternator is bad and if so how to check with duals?

 

The PCM controls the dual alternator set-up and times one out at the beginning of start-up, or so I'm told, so no worries there. As for the low voltage reading, it might be due to your glow plugs cycling at start up. They can stay on for over 120 seconds in extreme cold, and even in moderately cool temps, will routinely stay on for 60 seconds, so that could be your reason. Don't go by the WTS light on the dash, it's just basically a reminder, not an indicator of when they are on or not.

 

Absolutely the glow plugs - I've seen it a gajillion times. The glow plugs use a tremendous amount of juice when they are active, that's one of the key reasons for two batteries under the hood. While the glow plugs are cookin', the alternator(s) isn't/aren't exactly charging the batteries - it's just a game of keep-up for a minute or two.

 

Thanks for the info, it is 43 degrees down here. That is cold for South Texas.