JLG 1500SJ Operator Manual - Manual (Page 150)

SECTION 5 - LCD DISPLAY PANEL - GENERATION 1 & 2
5-54 – JLG Lift – 3121261
AXLES RETRACTED IN OUT OF TRANSPORT POSITION
When the axles are retracted and the machine is in the out of
transpor t position, the display will switch between axles
extended and retracted every 0.5 seconds to tell the operator to
extend the axles so the boom can be raised.