What F4 Means on a Legacy Thermador SC/SM Wall Oven: Shorted Oven Sensor or Under 40 F

What F4 means

F4 on older Thermador SC, SCD, SM and SMW ovens covers two readings: a shorted oven sensor, or a sensor temperature below 40 F. In a normal kitchen the second one means the signal is wrong, so the sensor wiring is the first suspect. The sensor should read about 1050 ohms at room temperature, and a short pulls that reading far off.

Usual causes of F4

Short in the oven sensor wiring
Sensor resistance that is outside the expected figure of about 1050 ohms at room temperature

✓ A safe check worth trying

1. Let the oven cool, then touch OFF or switch off at the breaker. 2. Wait 3 minutes and restore power. 3. If F4 flashes again, write down the code and model number. 4. Do not unplug or test the sensor. That is a technician task.

! Why you should stop here

The sensor is measured with a meter at the oven's plug
A short in hidden wiring needs tracing
We separate sensor trouble from board trouble before quoting

Taking off a panel yourself does not by default void a manufacturer warranty, yet it can lead to accidental damage, and some manufacturers attach their own service terms. Read your warranty paperwork, or ask us, before you decide.

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More Oven codes

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F4F4 questions

Why would an oven think it is under 40 F?

A shorted sensor sends a signal that looks like a very cold reading. The control cannot sort real cold from a bad circuit, so it stops and shows F4.

How is F4 different from F3?

F3 is an open sensor circuit and F4 is a shorted one. Same part, opposite electrical behavior, and both are tested with a meter. Mention anything unusual you heard, such as clicking.

Do I need to replace the sensor?

Maybe, but we measure first. If the sensor reads correctly, the issue lies in the wiring or the control, and we say so in the quote.