The 2 most common part(s) or condition(s) which cause the symptom Oven fan keeps running are listed below starting with the most likely. Check or test each item and watch any available videos.
RepairClinic Item # 3015163
The oven control board has a set of relays that turn on and off power to the bake, broil and fan circuits according to the customer settings and sensor input. If the oven fan keeps running, one of the relays might have shorted out. You can check the wiring diagram and with a meter check for voltage out from the control board. If voltage is always present from the fan relay, it is shorted and the control board will need to be replaced.
RepairClinic Item # 589857
If the oven fan keeps running after the oven is shut off, the convection motor might be shorted out. Remove the convection motor to inspect it for damage. Use an Ohm meter to see if it is shorted to ground. When an oven fan keeps running and the convection motor is at fault, the convection motor will have to be replaced, it is not repairable.