Service 4WD light on

Hello, I'm Danny.

This means you have a code stored in your trucks computer that was sent from the automatic transfer case. The first thing that needs to be done is to retrieve the code or stores that are stored. If you don't have access to a scanner or code reader most auto parts stores have a tool loaner program and can rent you one. Auto parts stores like AutoZone will check codes for free. Here is a tutorial that shows what is involved on how to check codes:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

After you perform this get back to us with the code information and we can then properly diagnose. I've attached a picture description below for your vehicle. Hope this helps and thanks for using 2CarPros.