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@nikihutchins
The 4x4 is manual operated by a cable. I would first try adjusting the cable by tightening up the lever notated in the pic. The other lever is the diff lock. If this does not fix it then something inside has gotten hung up, but lets hope not! I would even try disconnecting the cable and trying to work it free before I decided to take it apart. It would be a good days job to remove, clean, and re-install.