I have a similar problem with a GE Spacemaker XL1800 Microwave.
The panel displays an F3 Code and the Fan will self-start on High, drop to Medium, then to low. If I use a hair dryer to blow on the touch pad with warm air, after a few minutes I will be able to clear the F3 code and turn off the fan. This will sometimes fix the problem for several weeks or days. but the problem keeps coming back.
Model: JVM1860CF001
SN SF908883S
Color: Beige