Hi Dave,
Check the oven sensor for continuity. The normal reading should be about 1100 Ohms at the room temperature. If the reading is correct, replace the control board.
- The oven sensor
Part number: AP4326911 
- The control board
Part number: AP3837679 
Here are the breakdown diagrams and
Replacement parts for WHIRLPOOL GR448LXPB0 30" ELECTRIC CERAN FREESTANDING RANGE SELF CLEAN OVEN | AppliancePartsPros.com
Gene.