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Error code reference

LG Refrigerator Error Code I/M-Sensor Error

Sensor system in Ice Maker (FZ) has error.

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Sensor system in Ice Maker (FZ) has error.

First step from the service manual

Check voltage at MAIN PCB CN90-8 to CN90-4; should be 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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  • Wiring diagram references and connector pinouts from the OEM service manual
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What I/M-Sensor Error means on a LG refrigerator

The I/M-Sensor Error on an LG refrigerator indicates a fault within the ice maker's sensor system, specifically in the freezer compartment. This error is triggered when the main PCB detects an abnormal signal from the ice maker temperature sensor, which is responsible for monitoring conditions inside the ice maker unit. The sensor feeds real-time temperature data back to the control board, and when that signal falls outside acceptable parameters, the board flags the fault to prevent improper ice production or potential component damage.

The primary diagnostic starting point is checking the voltage at the main PCB connector CN90, specifically between pins 8 and 4. Under normal operating conditions, this voltage should read between 1.0V and 4.5V. A reading outside this window points to either a failed sensor, a wiring fault between the sensor and the PCB, or in some cases a defective main PCB that is misreading an otherwise functional sensor circuit.

Common failure points include a sensor that has drifted out of its calibrated resistance range due to age or moisture exposure, damaged wiring harnesses in the freezer compartment that can crack or short from repeated temperature cycling, and loose or corroded connector pins at CN90. Proper diagnosis requires a multimeter to verify voltage at the board connector and, if voltage is out of range, tracing back through the harness to isolate whether the fault is in the sensor itself or the wiring circuit.

Source: manufacturer service documentation.

Common causes of I/M-Sensor Error

  1. 01

    Faulty ice maker temperature sensor

    Part replacement

    The sensor itself may have failed or drifted outside its normal operating range, producing a voltage signal outside the 1.0V to 4.5V window expected at CN90 pins 8 to 4. Replacing the sensor is the most common fix when wiring checks out normal.

  2. 02

    Damaged or broken wiring harness

    Part replacement

    Wiring in the freezer compartment is subject to repeated thermal stress and can develop cracks, breaks, or shorts over time. Inspect the harness running from the ice maker sensor to the main PCB connector CN90 for any visible damage or continuity issues.

  3. 03

    Loose or corroded connector at CN90

    Wiring / connection

    The connector at CN90 on the main PCB can develop poor contact due to corrosion or an incomplete connection, causing an intermittent or out-of-range voltage reading. Disconnecting and reseating the connector, and inspecting the pins for corrosion, can resolve this without parts.

  4. 04

    Moisture or ice buildup around the sensor

    Wiring / connection

    Excessive frost or ice accumulation around the sensor can interfere with its readings or physically damage the component. Defrosting the ice maker compartment completely and checking sensor condition afterward can rule this out.

  5. 05

    Defective main PCB

    Part replacement

    If voltage at CN90 pins 8 to 4 reads correctly and the sensor and wiring pass inspection, the main PCB itself may be misinterpreting the sensor signal. Board replacement is typically a last resort after all other components have been confirmed good.

See the test procedure for each cause

Frequently asked questions about I/M-Sensor Error

What does I/M-Sensor Error mean on a LG refrigerator?
The I/M-Sensor Error means the refrigerator's main control board has detected an abnormal signal from the temperature sensor located in the ice maker. The board monitors voltage at connector CN90 between pins 8 and 4, expecting a reading between 1.0V and 4.5V. When the signal falls outside that range, the error code is triggered. This can point to a failed sensor, a wiring problem, or a connector issue.
Can I fix the I/M-Sensor Error myself on my LG refrigerator?
Some causes of this error are DIY-friendly. You can start by inspecting the wiring harness running from the ice maker to the main PCB for visible damage, and by reseating the connector at CN90. If you have a multimeter, checking the voltage at CN90 pins 8 and 4 will help confirm whether the sensor or board is at fault. Sensor replacement is a moderate-difficulty repair, while main PCB replacement is more involved and may benefit from a professional technician.
Is the I/M-Sensor Error on an LG refrigerator a safety concern?
This error does not typically present a safety hazard to you or your home. It primarily affects ice maker operation and can prevent proper ice production. Food stored in the main refrigerator and freezer compartments is not usually at risk, but you should monitor temperatures to confirm the freezer is maintaining safe levels while the issue is present.
How much does it cost to repair an I/M-Sensor Error on an LG refrigerator?
Repair costs vary depending on the root cause. A replacement ice maker temperature sensor typically costs between 15 and 50 dollars for the part alone. A main PCB replacement is significantly more expensive, ranging from 150 to 400 dollars or more for the part. Adding professional labor, total repair costs can range from around 100 dollars for a simple sensor or connector fix to 400 dollars or higher if the main board needs replacement.
Will resetting my LG refrigerator clear the I/M-Sensor Error?
A reset may temporarily clear the error code from the display, but if the underlying fault in the sensor, wiring, or connector has not been corrected, the error will return. Resetting the unit without diagnosing the root cause is not a long-term solution. Use the reset as a way to confirm whether the error comes back after a repair, rather than as the repair itself.

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