I just recently bought my first 6.0 so I am completely new to powerstrokes and diesels as a whole so please take it easy on me haha. I had my mechanic go through and fix everything. I have been getting the P1378 code alerting me the FICM has low voltage. I am not 100% sure why this is happening. I have read this can possibly happen because of bad batteries. I have no clue last time they were replaced and when looking at them, they appear to be two different sizes so I’m wondering if the voltage can be throwing this off. I am not sure if this matters, but I’m also getting a fuel level sensor code as well. Like I said, I’m completely new to diesels so please be patient with me haha. I would love any help or recommendations on what I should do. I want to learn about the truck and try to fix things myself before having to take it to a mechanic. Thank you in advanced