Abstract: The lost motion arm 44 has first and second contact surfaces 102 and 104. A latch mechanism is connected on the body with an extendable plunger 120 having a first contact surface 124 and a second contact surface 126. The plunger 120 has a first position for first contact surface 124 engagement with the lost motion arm first contact surface 102 to prevent angular movement of the lost motion arm 44 with respect to the body 10 in a first angular direction. When angular movement in the first angular direction is prevented, the motion of the lost motion arm 44 imparted by the cam lobe 66 is transmitted to the body 10 to provide for a first state of operation of the valve stem 18. When the plunger 120 is in a second position, non-contacting with the lost motion arm 44, the lost motion arm 44 is allowed to pivot relative to the body 10. Accordingly, the rocker arm assembly 7 will be in a second state of total or partial deactivation of the valve stem 18.