GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hello and thank you for your question,When you say you have no power , is everything dead, do the light come on?
Okay what model ( 1500 or a 2500) is your Sierra and your engine size?
Gas correct ?How many batteries?
There are two mega fuse located in the engine compartment (right rear) . Have a look at the wiring diagram in the link below and start with checking them to see if either one is blown.https://dl.dropboxusercontent.com/u/104923897/Mega%20fuse%20Jul%2023.pdf
Okay if the mega fuse check ikay then what about all the fuse in the under hood panel, are you getting power on them?
If you sure its the BCM then it would have to be replaced , have to tried to scan the system and see if there are any fault codes coming?
I sure would do that before you start replacing parts that may not be needed. If the complete electrical system is dead then I suspect you have a connection issue someplace and its going to be a mater of tracking it down.