LG Refrigerator Er FS: The Freezer Temperature Sensor Cannot Read

Er FS means the freezer compartment temperature sensor (NTC thermistor) returned a resistance value outside the board's valid range. This sensor tells the board the current freezer temperature, which the board uses to decide when to run the compressor, how long defrost cycles should last, and whether temperature is within the user's setpoint. Without valid data, the board loses control over freezer temperature regulation.

Immediate Impact

The board cannot determine the freezer temperature. Depending on the LG model's failsafe programming:

• Some models run the compressor continuously on maximum output (safe for food but high energy consumption)
• Some models cycle the compressor on a fixed timer pattern regardless of actual temperature
• The display shows an incorrect or default temperature reading

In either case, the freezer may overcool (reaching -15 to -20 degrees F) or undercool (rising above 10 degrees F) because the board is operating blind without sensor feedback.

Testing the Freezer Sensor

The freezer thermistor is a small capsule sensor mounted inside the freezer compartment, typically clipped to the upper wall or near the air inlet vent. On some models it is behind a small cover plate.

1. Unplug the refrigerator
2. Locate the sensor inside the freezer (consult the tech sheet for your specific model's sensor location)
3. Disconnect the sensor's 2-wire connector
4. Measure resistance with a multimeter:
   • At approximately 0 degrees F (normal freezer temp): expect 15,000-22,000 ohms
   • At room temperature (if removed and brought to ambient): expect 5,000-6,000 ohms
5. If infinite (open) or near zero (shorted): sensor is dead. Replace it.
6. If resistance reads within range at room temp but the fridge still shows Er FS: reconnect and check the harness for continuity from the sensor connector to the main board connector

Sensor Replacement

The freezer sensor is one of the simplest refrigerator repairs:

1. Unplug the refrigerator
2. Inside the freezer, locate the sensor (often behind a small plastic clip or cover on the upper wall)
3. Pull the old sensor from its mounting clip. Disconnect the wire connector
4. Connect the new sensor (6615JB2005H or model-specific, $8-18). Push into the mounting clip
5. Plug in and verify the freezer display shows a plausible temperature. It will take 1-2 hours to read accurately as the sensor equilibrates to compartment temperature

Parts and Cost

Er FS vs. Er RS: Which Compartment

LG refrigerators have separate sensors for the freezer (FS) and refrigerator (RS) compartments. Er FS is the freezer sensor; Er RS is the fridge sensor. Each sensor fails independently. Both are NTC thermistors with similar testing procedures but different resistance ranges due to their different operating temperatures.

If both Er FS and Er RS appear simultaneously, suspect a shared wiring problem or a main board failure rather than both sensors dying at the same time.

Overcooling After Er FS

If the freezer is running excessively cold with Er FS active (ice cream is rock-hard, food is deeply frozen), the board is in failsafe mode — running the compressor at maximum. This wastes energy but protects food. The fix is replacing the $8-18 sensor, which returns the board to normal regulated operation.

Door Sensor Interaction

Some LG models temporarily suppress temperature sensor readings when the door is open (the board knows the sensor will read warm air from the room). If Er FS appeared after the freezer door was left ajar, verify the door is fully closed, then power cycle the unit. If Er FS clears, it was a momentary reading anomaly, not a sensor failure.

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LG freezer running too cold or too warm? Er FS is a $8-18 sensor with a 10-minute replacement — we test before we swap. Book sensor diagnosis.