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Discussion Starter #1
Finally had this happen to me today. Had an EMS call and didn't let the truck warm up as normal. Everything was fine when I got back to the truck after the call and upon startup the light & DIC message was gone.

From the GM Bulletin...

A Service Charging System message may be displayed on the DIC and/or a low voltage reading may be shown on the volt gauge during the first several minutes after a cold start on some 2007-2010 Silverado or Sierra models equipped with the 6.6L diesel engine (RPO LMM). Some modules may set DTC B1517, SYM 03-Battery Voltage below Threshold.

If this condition only occurs during the first several minutes of a cold start, no repairs should be made. This is a normal operating characteristic of vehicles equipped with the diesel engine.

During a cold engine start (Cold is an engine coolant temperature below 100° F or 40° C), the intake air heater and the glow plugs are commanded on to help reduce emissions and improve cold weather driveability. The intake air heater can draw 130 amps at 100% duty cycle for up to 10 minutes. The glow plugs can draw up to 110 amps with cycle times up to 3 minutes. These two loads, in addition to the normal loads from the vehicle (example: blower, lights, heated seats, etc.), can exceed the maximum generator output (125 amps in most cases). Due to these high current loads, the Service Charging System message may display during the first several minutes after a cold start.
 

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Sounds normal, may want to load test your batts separately and make sure they're up to par for your On-Call duty. One in the pair could be on it's way to failure, pulling down the other and reducing the available amps for cold startup, stressing the alt to max and throwing a code.
 

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Discussion Starter #3 (Edited)
Both batteries where replaced when I got the truck a month or so ago. Checked voltage when I got in to work and both batteries were up to 12.8v after sitting 40 minutes or so. I will load test the alternator this weekend when I take the kids to see their grandparents at my dads shop to ensure it is charging right but as for now all looks fine. Of course if it continues will check it sooner...

P.S. After thinking some more I can see your point in the fact that maybe I should still load test the batteries also. Just cause they are new doesn't mean one couldn't be on the way out the door like you said. If I find any faults in the batteries or alternators I will update but if not will chalk it up to the above bulletin.
 

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Chances are its normal, Mine did this before I got my intake heater deleted (battery voltage comes right back up within a minute, before it would be 3-5 with the intake heater on) . It seems as if the intake heater actually serves no function in cold starting other than to draw your batteries down, Pretty sure its more of an emissions thing than anything.
EFI live can fix the intake heater problem.
 

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Discussion Starter #5
I went about 1.5 miles before the battery light & DIC message came on..Probably not to help it any I was on it pretty hard for being cold...
Thinking back I had the Blower on high, Radio on, IQ running, GPS, rear defrost & heated mirrors on, heated seat on, and LED Emergency lights on dash and grill running. So I had plenty of draw. LOL
 

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Discussion Starter #6
Pretty sure its more of an emissions thing than anything.
Yep I would say your totally right due to the fact that is even what the bulletin states..
the intake air heater and the glow plugs are commanded on to help reduce emissions and improve cold weather driveability
 

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Glow plugs are definately needed to get the thing started, without those you'd have a hell of a time starting the truck when its below freezing (A friend of mine has a bad glow plug controller and knows just how much it sucks)

I think the light is on a delay so if the batteries dont come up to normal voltage within the time allotted then the service light comes on. Mine would also take about 1-2mi to come on and would stay on until I restarted the truck.
 

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Discussion Starter #8
Yes, most definitely need the glow plugs for start but I was referring to more like you said before the intake air heater not being needed. Sorry for the confusion!
 
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