Jumper cables incorrectly connected to the 2011 Chevy Silverado 3500 6.6 Duramax with Allison tranny. Now truck is D E A D
What do we check first? PS The truck was fine but the tractor needed jumped.

 

If you haven't unhooked the jumper cables, do so. Let it set for a couple hours. It might come back. I'll also ask if the battery is ??? old, it' needs replaced.

 

Thanks I will try that first. I wondered if that would work, its worth a try.

 

Check the Main Fuse.

 

Check the megafuses on the firewall, on the passenger side. IIRC, you'd have a 125-amp and a 175-amp in there. I'd wager that one of them got fried. They cost like $8 at an auto parts store.

Here's the location, circled in yellow. The cover just pulls off:


Once you've pulled the cover off, you'll see this:


If these are both intact, then it's likely that something got fried, like the powertrain control module, or the body computer.