Water level sensing in LG washers is done differently from how you may be used to seeing it done in other brands. Whirlpool, GE, Electrolux and others use an air tube connecting an air dome on the tub to a pressure sensor with a physical diaphragm or transducer that "feels" the water level increase as an increase in pressure inside the air tube. LG uses frequency measurements. How's that again? I'll let Brother john63, Dean of LG Appliantology explain:
The Water Level Frequency Sensor operation is based on the displacement of the *coil* attached to the diaphragm.
When the *coil* raises or lowers---it changes the electronically resonant characteristics of the oscillator circuit.
The water level is measured by the Main Board---by frequency readings.
I've never had a failed Water Level Sensor.
It is best tested while on the washer---by using the TEST MODE.
On most LG washers---the Test Mode is enabled by pressing and holding the SPIN SPEED and SOIL LEVEL buttons---and then pressing the POWER button (release all 3 buttons and wait for the door to lock).
Press the START / PAUSE button 4 times at one second intervals (Prewash Cold Water Fill)
The display read-out on the Control Panel will show the *frequency*
Empty---the frequency read-out should be about 255
A tub full of water should show a frequency of about 214 (depending on model number)
Some of the errors that can be displayed---relating to water fill are...
Little or no water---usually caused by a failed Water Valve
Too much water (overflow detected)---Can be a failed/stuck open Water Valve or blockage in the black air tube which is connected to the Water Level Frequency Sensor. Disconnect the tube from the sensor---and blow air back into the tub to clear obstruction.
To test the Water Level Frequency Sensor outside of the washer...
Use a test meter to check the ohms between pins 1 and 3 (should have between 21 & 23 ohms).
Source: LG PRESSURE SENSOR OPERATION