My truck also had the cel on. Scanned it and showed the P2509 code. I cleared it, but it came back. If I drive the truck all day, the light shuts off. This has been going on for about two weeks.
Checked all the connections and grounds, everything looked fine. Took it to have the batteries checked and they were both bad!
Replaced the batteries and cleared the fault code, cel off. Let's see if that does it! Never had batteries fail in that manner before. They usually just die! These however still had the ability to start the truck.
Four years to the day on the original batteries. Not bad considering how hot it gets here in the summer.