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Error code reference

LG Oven Error Code F-5

Lower oven thermistor is shorted for over 1 minute after cook starts.

LG codesLG oven codes

Lower oven thermistor is shorted for over 1 minute after cook starts.

First step from the service manual

Check the thermistor using test mode 4.Diagnosis; verify sensor value is 70°F–90°F at room temperature. If not, power off and measure thermistor resistance at CN05 — normal is approximately 1.09 kΩ.

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

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What F-5 means on a LG oven

The F-5 error code on an LG oven indicates that the lower oven thermistor has detected a shorted condition continuously for more than one minute after a cook cycle begins. The thermistor is a temperature-sensing resistor located inside the oven cavity that feeds real-time temperature data to the control board. When the thermistor shorts, its resistance drops abnormally low, causing the control board to receive a false temperature signal. Rather than allow the oven to operate on faulty sensor data, which could result in uncontrolled heating, the control board halts the cook cycle and displays F-5.

At room temperature, a properly functioning lower oven thermistor should produce a sensor value between 70°F and 90°F in test mode 4, corresponding to a resistance of approximately 1.09 kΩ measured at connector CN05. A shorted thermistor will show resistance significantly below this value, often near zero ohms. This low resistance tricks the board into reading an extremely high oven temperature, triggering the fault. The short can occur within the thermistor itself, in the wiring harness connecting it to the control board, or at the connector terminals.

Common causes include a failed thermistor sensor, damaged wiring between the sensor and the control board, or corroded and shorted connector pins at CN05. Physical damage from high heat exposure, grease buildup around the sensor probe, or a pinched wire routed near the oven cavity wall can all produce the shorted circuit condition. Diagnosing the fault requires entering test mode 4 to read the live sensor value, then powering off the unit and measuring resistance at CN05 to confirm whether the fault lies in the sensor itself or the associated wiring.

Source: manufacturer service documentation.

Common causes of F-5

  1. 01

    Failed lower oven thermistor

    Part replacement

    The thermistor itself has developed an internal short, causing its resistance to drop well below the normal 1.09 kΩ at room temperature. This is the most common cause and can be confirmed by measuring resistance at CN05 after powering off the unit.

  2. 02

    Shorted or damaged wiring harness

    Part replacement

    The wires connecting the thermistor to the control board may be pinched, melted, or chafed, causing two conductors to contact each other and create a short circuit. Inspect the full length of the harness from the sensor probe to connector CN05 for visible damage.

  3. 03

    Corroded or shorted connector pins at CN05

    Wiring / connection

    Grease, moisture, or heat exposure can cause the pins inside connector CN05 to corrode or bridge together, producing a false short reading. Inspect the connector for discoloration, debris, or deformed terminals.

  4. 04

    Thermistor probe contaminated by grease or debris

    Wiring / connection

    Heavy grease buildup around the sensor probe can in some cases contribute to erratic or shorted electrical readings. Cleaning the area around the probe and re-testing with test mode 4 can help determine if contamination is a factor.

See the test procedure for each cause

Frequently asked questions about F-5

What does F-5 mean on a LG oven?
F-5 means the lower oven thermistor has been detected in a shorted condition for more than one minute after a cook cycle starts. The thermistor is the temperature sensor inside the lower oven cavity, and when it shorts, it sends an invalid signal to the control board. The board shuts down the cook cycle and displays F-5 to prevent uncontrolled or unsafe heating.
Can I reset the F-5 error on my LG oven and keep using it?
Resetting the oven by cutting power may temporarily clear the display, but the F-5 error will return as soon as a cook cycle starts if the underlying fault still exists. Because the error is triggered by a sustained shorted signal from the thermistor, the root cause needs to be diagnosed and corrected. Operating the oven with a faulty temperature sensor is not recommended, as the control board cannot accurately regulate heat.
Is it safe to use my LG oven while the F-5 code is showing?
No, it is not safe to use the oven while F-5 is active. The error indicates the control board is receiving a faulty temperature reading from the lower oven sensor, which means the oven cannot properly regulate its heating elements. Using the oven in this condition could result in overheating or unpredictable temperature behavior.
How do I diagnose the F-5 error on my LG oven?
Start by entering test mode 4 and checking that the sensor value reads between 70°F and 90°F at room temperature. If the value is outside that range, power off the oven and use a multimeter to measure thermistor resistance at connector CN05. A normal reading is approximately 1.09 kΩ at room temperature. A reading significantly below that value confirms a shorted thermistor or wiring fault.
How much does it cost to repair a F-5 error on a LG oven?
If the fault is limited to the lower oven thermistor, parts typically range from around $20 to $60 depending on the specific model, and the repair is relatively straightforward for a technician. If the wiring harness is damaged or the control board is involved, total repair costs including labor could range from $100 to $300 or more. Getting a professional diagnostic first can help identify exactly which component has failed before purchasing parts.

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