GE Microwave Error Code F4

F4 on a GE microwave indicates a problem with the humidity sensor circuit. The control board has detected that the sensor is either open or shorted, meaning the resistance readings are outside the expected range. The code can also be triggered by an electrical surge or excessive line noise on the power circuit, even when the sensor itself is functioning correctly.

Start by unplugging the unit for one minute and restoring power. If the code returns, you or a technician will need to test the humidity sensor resistance at connector CN5 using a multimeter. Target values are 6.2K ohms across BLK-RED, and 3.1K ohms across both RED-WHT and BLK-WHT. If readings are off, the sensor or its wiring needs to be replaced. If readings are correct, the issue may be electrical noise on the line rather than a faulty sensor, and replacing the sensor will not fix it.

If only a power reset is needed, there is no parts cost. Humidity sensor replacement, if required, typically ranges from around $15 to $60 for the part depending on the model. Adding professional labor can bring the total repair cost to roughly $80 to $200. If the control board is the root cause, parts and labor costs will be higher, which may affect whether repair is economical compared to replacement.

Removing power for one minute is always the recommended first step when F4 appears. If the error was caused by a temporary power surge or line noise, the reset will clear it and the microwave should operate normally. If F4 returns after the reset, a hardware fault in the sensor or wiring is likely and further diagnosis is needed.

When F4 is active, the humidity sensor circuit is reporting a fault, which will disable sensor-cook and auto-cook functions that rely on steam detection. Using the microwave for basic timed cooking may still be possible, but operating the appliance with an unresolved error code is not recommended until the underlying cause is identified and corrected.