The general shape of the EE-SX6 is consistent with an IR detection module. Consider to move the extruder assembly as far away as possible, then power up. As the mechanism begins to move, insert a piece of plastic or paper into the slot to trip the sensor.

The statement that there's nothing in the area to move into the slot is fairly useful in this discussion. If the tripping causes the carriage to zero, you know there should be something to move into the slot.