KitchenAid Microwave F4 Error: Cavity Temperature Sensor
What Does KitchenAid Microwave Error Code F4 Mean? F4 on a KitchenAid microwave indicates a fault in the cavity temperature sensor — the thermistor that monitors interior oven temperature during convection, combination, and some sensor-based cooking programs. This code applies only to combination microwave-oven models (KMBP, KOCE, KMBS series) since basic microwaves do not have […]
Quick Assessment
Answer to continue safely
Is it safe to keep using?
Maybe. Standard microwave cooking is safe and unaffected. Convection, combination, and some sensor programs are locked out by the fault. Use only microwave-only modes until service.
Can I reset the code?
No. A power cycle does not repair a failed thermistor or broken wire. F4 returns as soon as a convection or combination cycle is requested, which is when the board reads the cavity sensor.
When to stop immediately?
Stop if you notice: F4 appears during any microwave-only cooking mode, Cavity temperature display shows impossible values during operation.
Symptoms You May Notice
Convection and combination cooking modes disabled
Attempting to start a convection bake, roast, or combination cycle produces F4 immediately. Straight microwave cooking remains available on non-combination models.
Temperature display stuck at a fixed or impossible value
The cavity temperature display shows a constant reading regardless of actual oven temperature, or shows an obviously impossible value like 000 or 999.
Convection fan runs but element does not heat
During a convection cycle, the convection fan activates but the heating element never turns on because the control board cannot verify cavity temperature feedback.
Possible Causes
Failed cavity thermistor
The NTC thermistor mounted inside the cavity has failed open or short, typically after long-term exposure to cooking temperatures and cleaning cycles. This is the most common cause on combination microwave-ovens.
Requires ProfessionalThermistor harness pinched or unplugged
The two-wire harness running from the cavity thermistor to the main control board has come unplugged from a prior service call or been pinched by a cavity liner screw.
Requires ProfessionalControl board thermistor input failure
The analog input on the main board that reads the thermistor channel has failed, producing an out-of-range reading even with a good sensor installed.
Requires ProfessionalSafe Checks You Can Do
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1
Continue using standard microwave functions
Until service is completed, use the basic microwave cooking modes. Time Cook, Power Level, and Defrost all operate independently of the cavity thermistor and remain fully functional on combination models.
Sensor Cook may or may not work depending on the specific model — if it depends on cavity temperature in addition to humidity, it will be disabled alongside Convection.
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2
Schedule a technician and note the model number
Have the model and serial number ready when calling for service. Combination oven-microwave thermistors vary between KMBP, KMBS, and KOCE series — the correct replacement part depends on the model.
Photograph the rating plate inside the door frame before calling — it makes parts sourcing considerably faster.
When to Call a Professional
Contact a qualified technician if:
- Thermistor replacement restores convection and combination modes
- Thermistor resistance measures infinite or zero at room temperature
- Control board analog input measures bad with a known-good sensor
Need Professional Help?
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