Water Level Pressure Sensor Error.
1) Verify that the black tube is still connected to the Water Level Sensor at the top of the washer---and to the Air Bell at the bottom of the tub.
2) Remove the black tube from the Water Level Sensor---and blow into tube---to clear a possible blockage. Reconnect and test washer.
3) Water Level Pressure Sensors (6601ER1006E) *rarely* fail.
Source: LG Combo Washer/dryer not drying