It could be either of the two. If you have electric shift 4wd, start by checking if the actuator on the transfer case is getting power. If it is, remove the actuator and confirm that it is working. If that is okay, then you most likely have a vacuum leak to the front axle.
Check that and let me know what you find.
Joe
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Monday, April 12th, 2021 AT 11:14 AM