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Error code reference

LG Refrigerator Error Code 40E

Ice Room Sensor Error

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Ice Room Sensor Error — detected temperature above 149°F (+65°C) or below -58°F (-50°C).

First step from the service manual

Measure voltage between Main PCB CN78-10 and CN78-12; should read between 4.5V and 1.0V.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What 40E means on a LG refrigerator

The 40E error code on an LG refrigerator indicates an ice room sensor fault. The ice room sensor monitors the temperature inside the freezer's ice maker compartment, and the control system flags this error when the sensor reading falls outside the acceptable operating range, specifically when the detected temperature rises above 149°F (65°C) or drops below -58°F (-50°C). Either extreme is well outside the normal operating window for an ice room, which tells the Main PCB that the sensor signal is invalid rather than reflecting a true temperature condition.

The first diagnostic step is to measure the voltage at the Main PCB connector CN78, between pins 10 and 12. A healthy sensor circuit will produce a reading between 1.0V and 4.5V depending on the ambient temperature in the ice compartment. A reading outside this window, including a reading of 0V or 5V, points to either an open circuit or a short circuit in the sensor wiring or the sensor itself. This voltage-based check quickly distinguishes between a wiring fault and a failed sensor component.

Common causes include a failed NTC thermistor sensor, damaged or pinched wiring in the harness running to the ice room, a corroded or disconnected connector at CN78, or in less frequent cases a faulty Main PCB that is misreading a valid sensor signal. Ice buildup around the sensor can also physically damage sensor leads over time, leading to intermittent or permanent faults. Resolving the error typically requires isolating the fault through voltage and continuity testing before replacing any components.

Source: manufacturer service documentation.

Common causes of 40E

  1. 01

    Failed Ice Room NTC Thermistor

    Part replacement

    The temperature sensor itself has failed internally, producing a signal that reads as an open or shorted circuit. This is the most frequent cause and will show as a voltage outside the 1.0V to 4.5V range at CN78 pins 10 and 12.

  2. 02

    Damaged or Broken Wiring Harness

    Part replacement

    The wiring between the ice room sensor and the Main PCB can become pinched, frayed, or broken over time, especially near door hinges or areas exposed to repeated freezing and thawing cycles. Inspect the full harness length for visible damage or breaks.

  3. 03

    Corroded or Disconnected Connector at CN78

    Wiring / connection

    Moisture in the freezer compartment can corrode the connector pins at CN78 on the Main PCB, causing a poor or open connection. Check pins 10 and 12 for corrosion, bent pins, or a loose plug seating.

  4. 04

    Ice Buildup Around the Sensor

    Wiring / connection

    Excessive frost or ice accumulation around the sensor can physically stress or sever the sensor leads over time. A manual defrost cycle should be performed before testing to rule out ice contact as a contributing factor.

  5. 05

    Faulty Main PCB

    Part replacement

    If the sensor and all wiring test within spec but the error persists, the Main PCB itself may be misreading the sensor voltage. This is the least common cause and should only be considered after all other components have been confirmed good.

See the test procedure for each cause

Frequently asked questions about 40E

What does 40E mean on a LG refrigerator?
The 40E code indicates an ice room sensor error. The refrigerator's control board has detected a temperature reading from the ice compartment sensor that is above 149°F (65°C) or below -58°F (-50°C), which are impossible real-world values for that compartment. This tells the board that the sensor or its wiring circuit has a fault rather than an actual temperature extreme.
Can I fix a 40E error myself?
Some causes of the 40E error are DIY-friendly, such as reseating a loose connector at CN78 or clearing ice buildup around the sensor after a manual defrost. However, accurately diagnosing the fault requires a multimeter to test voltage between CN78 pins 10 and 12, and replacing the thermistor or wiring harness involves working inside the freezer compartment. Technicians with basic electrical testing skills can often handle this repair, but those unfamiliar with connector testing may prefer professional service.
Is a 40E error code on a LG refrigerator dangerous?
A 40E error is not a safety hazard in the way a gas leak or electrical fire would be. However, if the ice maker system is not functioning correctly due to this fault, ice production will be affected and the ice compartment may not maintain proper temperatures. Food safety is not typically at immediate risk since the main fresh food and freezer compartments operate independently, but the issue should still be diagnosed and repaired promptly.
Will resetting the refrigerator clear the 40E error?
A power reset may temporarily clear the 40E error code from the display, but if the underlying sensor or wiring fault is still present, the code will return once the control board runs its self-diagnostic cycle again. A reset is useful for confirming whether the fault is intermittent, but it is not a repair. The root cause must be identified and corrected to permanently resolve the error.
How much does it cost to repair a 40E error on a LG refrigerator?
Repair costs depend on the root cause. If only the ice room thermistor sensor needs replacement, parts typically range from roughly $15 to $50, and a technician's labor for diagnosis and replacement may add $80 to $150 depending on your location. If the Main PCB is the cause, board replacement costs can range from $150 to $350 or more for parts alone, making professional diagnosis before parts ordering particularly important for this code.

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