7/8/20: UPDATE: Dealer thinks they found the problem: Loose UBEC Bolts. There was a recent bulletin posted on 6/26/20 about this that may be the cause for this issue as a whole. Ask for document ID 5628169 or the following title for the GM bulletin: #PIT5756: Various Electrical Concerns (Inspect UBEC Bolts for Being Loose) - (June 26, 2020). SEE ATTACHED
Condition: Some customers may comment on any number of electrical related symptoms. The following are some of the known reported ones:
no crank
no start
starter grinds or re-engages after engine starts
SES MIL
IPC guages sweep/fluctute and/or various IPC warning lights or messages
High or low system voltage
May have any of the following DTC's: B1325, B2750, B305D, B297B, C0049, P0562, P0700, U0100, U0101, U0102, U3006
some of these concerns may be noticed with powertrain movement, like when accelerating or braking.
Cause: These concerns could be caused by the X50A underhood fuse box bolts being loose. The X50A has built in indicators which pop up as the X50A bolts are tightened down, to inidcate the X50A is fully installed. In some cases, even if these green indicators are popped up, the bolts may still be loose.
Correction: Inspect the X50A Underhood Fuse Block bolts and verify they are properly torqued to 53 lb in (6Nm)
Dealer stated that my box was indeed loose (that's what she said). Has not been able to replicate issues. Really hoping this is the fix for my truck and all of yours. Will update forum either way. Best of luck.
UPDATE: 7/14/20. I have had no issues with the truck so far. I start and drive it every day. I really hope this was the simple fix; hopefully you guys give it a try and it works. You can do this fix yourself. I've attached the bulletin for everyone here. Good luck.
BUELLTIN (1).pdf 1.02 MB · 36 downloads
Thanks for the fix! Tripped both P0700 and U0100 today and found this. Those 4 bolts were only at about 15 inch-pounds, and the green indicators were up. Talked to my service rep at the dealer to cover my arse and not void anything. Tightened them to 53 and the CEL was off at the next start!!!