Since the broil works in the top oven, that would indicate that the temperature sensor is working as well. Most likely you'll need to replace the bake element.
The first thing to check is the bake element. You can remove and disconnect the bake element and test it for continuity with an Ohm meter.
NOTE: Disconnect the oven from the power source before servicing, or turn the oven breaker off.
If the bake element measures resistance, the oven control and the relay board will need to be check for voltages.
This oven has a hidden bake element. The steps in this repair guide should help you: searspartsdirect.com/diy/repair-guide/how-to-replace-a-wall-oven-hidden-bake-element
You can find parts and diagrams on Sears PartsDirect: searspartsdirect.com/model/2e3f71r4ip-000582/kenmore-79049443413-electric-wall-oven-parts
Look at the "Upper oven diagram" on the above link to see where the bake element is located (under insulation and a shield). You'll need to remove both to access the bake element.
This is your Bake Element replacement: searspartsdirect.com/product/1igp8dpwk9-0022-628/id-808650402
I hope this helps!
You can call Sears Home Services, if you'd like a professional repair at 1-800-4-MY-HOME.