09 Sierra 12v Battery Unhooked for 8 Months- Hybrid Battery Ok?
 

Hi Everyone,

I have an 09 Sierra 4X4 6.0 Hybrid that finally experienced the dreaded AFM lifter failure at 212K miles. I have had the truck down while rebuilding the engine on the side. The rebuild consisted of cylinder honing, having the heads done, replaced cam, cam bearings, all lifters, lifter trays, VLOM, oil pump, and crank shaft center line checked. Basically a brand new engine. I am finally getting to the point where the truck is ready to fire back up. My concern is that while I have been working on the engine, I have had the 12v battery unhooked. Is this going to cause a problem with my Hybrid battery? Ultimately resulting in the truck not to start when I turn it over soon?

Note: I have had the 12v hooked back up for 3 days on a trickle charge to ensure it is good to go when the time comes.

Any advice or direction to beneficial information would be greatly appreciated.

Re: 09 Sierra 12v Battery Unhooked for 8 Months- Hybrid Battery Ok?
 

Highly likely that it's toast. Aged and high-mileage HV batteries tend to drop multiple cells and are ruined.

Personally, I recommend you remove the battery and check all 40 module voltages before attempting to start.