The F31 fault code indicates a problem with the oven temperature sensor probe. The temperature probe is secured in the top of the inside back wall of the oven. Unplug the range
to disconnect electrical power. Open the oven door and remove the racks. Remove the screws that secure the oven temperature sensor probe in the back wall of the oven. Carefully pull the sensor into the oven until you get to the wire harness disconnect plug. Unplug the sensor probe. Do not let the wire harness **** back through the opening in the back of the oven. Check the resistance of the probe with a volt/ohm meter. At room temperature, you should measure about 1100 ohms of resistance. Since you are getting the F31 fault code, you will not likely measure this resistance. If the resistance is bad, replacing the oven temperature sensor probe .This should fix your problem. You can order this part from the www.appliancehelponline.com
If the resistance of the temperature probe is normal (1100 ohms), then I recommend that you access the electronic oven control board in the console (with the range still unplugged ). Remove the upper back panel. Pull the P5 connector on the control board and measure the resistance through the purple wires (pins 12 and 13 as shown below) to check the resistance of the temperature probe through the circuit that connects to the board. If the resistance is drastically different than the 1100 ohms measured at the probe, then the wire harness is bad and will need to be replaced. If you measure the proper resistance through this wiring harness at the control board and the connections are good, then the electronic oven control board will need to be replaced.