Shift to 4L can only be done with transmission in NEUTRAL.
Normal setup is this:
left forward: 2WD
left aft: 4H
then from there it can be moved to the right but stick will not go forward to 4L except if transmisison is in NEUTRAL.
Then, as you start pushing forward, there is a transfer case NEUTRAL position before reaching 4L. WIth the manual T-case, there is a notch at that position, but not with the auto...nevertheles, if T-case lever is maintained in that intermediary position, it will neither go forward nor reverse...but as this is an unstable condition, the lever can move by itself to 4H or 4L with undesirable consequence like a loud clank if transmission is in a forward or reverse range..