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Error code reference

LG Microwave Error Code E-31

Weight Sensor Open Error (when value of HEX is above FF for 5 seconds).

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Weight Sensor Open Error (when value of HEX is above FF for 5 seconds).

First step from the service manual

Check sensor.

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

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What E-31 means on a LG microwave

The E-31 error code on an LG microwave indicates a Weight Sensor Open Error. This fault is triggered when the hexadecimal value returned by the weight sensor circuit rises above 0xFF (decimal 255) and remains there for a continuous period of 5 seconds. The weight sensor is used in models that feature auto-cook or sensor-cook functions based on food weight, allowing the microwave to adjust cooking time and power level automatically. When the sensor's signal output exceeds the valid readable range, the control board interprets this as an open circuit condition in the sensor or its associated wiring.

An open circuit in the weight sensor circuit can result from a broken sensor element, a disconnected or damaged wiring harness connector, or a failed solder joint on the sensor board. Because the control board reads the sensor value continuously and compares it against defined thresholds, any interruption in the signal path will cause the value to peg at or above the 0xFF threshold, triggering the 5-second timer and setting the fault. Physical damage to the sensor from moisture, heat, or mechanical stress are also common contributors.

Diagnosing this error begins with a direct inspection of the weight sensor itself, including its connector, wiring leads, and mounting condition. Technicians should check for continuity through the sensor circuit and verify that connector pins are fully seated and free of corrosion. If the sensor reads out of range under all conditions, replacement of the sensor assembly is typically required. The control board should also be evaluated if a new sensor does not resolve the fault.

Source: manufacturer service documentation.

Common causes of E-31

  1. 01

    Faulty or failed weight sensor

    Part replacement

    The weight sensor element itself may have failed internally, causing its output to read above the valid range. This is the most likely cause when no visible wiring damage is present.

  2. 02

    Disconnected or loose sensor connector

    Wiring / connection

    The wiring harness connector linking the weight sensor to the control board may have come loose or partially unseated, interrupting the signal. Inspect all connector points along the sensor circuit for proper seating.

  3. 03

    Damaged sensor wiring harness

    Part replacement

    Wires running from the weight sensor to the control board may be pinched, cut, or have broken insulation, creating an open circuit. A continuity check along the harness will identify any break.

  4. 04

    Corrosion or moisture at connector pins

    Wiring / connection

    Moisture or grease buildup inside the connector can cause high resistance or an open condition at the pin contacts. Visually inspect for discoloration, oxidation, or residue on the connector terminals.

  5. 05

    Control board input circuit failure

    Part replacement

    If the sensor and all wiring check out correctly, the input circuit on the main control board that reads the sensor signal may have failed. This is the least common cause and is typically diagnosed after ruling out all sensor and wiring issues.

See the test procedure for each cause

Frequently asked questions about E-31

What does E-31 mean on a LG microwave?
E-31 on an LG microwave indicates a Weight Sensor Open Error. The microwave detected that the weight sensor's output value exceeded the maximum readable hexadecimal value of 0xFF for 5 or more consecutive seconds, which the control board interprets as an open or broken circuit in the sensor system. This fault disables weight-based auto-cook functions until the sensor circuit is repaired.
Can I fix an E-31 error on my LG microwave myself?
Some causes of E-31 can be addressed without replacing parts, such as reseating a loose connector or cleaning corroded terminals. However, if the weight sensor itself has failed, it will need to be replaced, which requires disassembling the microwave. Because microwaves contain a high-voltage capacitor that can retain a lethal charge even when unplugged, internal repairs should only be performed by a qualified technician unless you are experienced with high-voltage appliance safety procedures.
Is it safe to use my LG microwave when it shows E-31?
The E-31 error specifically affects the weight sensor circuit, which is used for automatic cooking programs based on food weight. Basic microwave heating functions may still be available, but you should not ignore the fault or attempt to use the appliance if it is behaving erratically. It is best to have the sensor circuit inspected before continued regular use.
Will resetting my LG microwave clear the E-31 error?
A power reset by unplugging the microwave for a few minutes may temporarily clear the error display, but if the underlying weight sensor circuit problem still exists, the E-31 code will return once the control board reads the sensor again. A reset alone does not repair the open circuit condition that triggers the fault.
How much does it cost to repair an E-31 error on an LG microwave?
Repair costs for an E-31 error vary depending on the root cause. If only a connector needs reseating or cleaning, the cost may be limited to a service call fee, typically in the range of $75 to $150. If the weight sensor requires replacement, parts and labor combined can range from $100 to $250 or more depending on the specific model and local labor rates. If the control board is at fault, costs will be higher.

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