ISX 12 code 4726 and 0559

[FarmLife]

Removed the high pressure fuel pump head. Put shop air to the port on the front of the pump to extend the plungers. The plungers would not move. Was able to take off the springs and pull the plungers up by hand. When you push the plungers down they come back up like they should. Since the plungers would not extend with shop air does this mean the check valves in the top of the head are stuck?