Diagnosis
The quartz heating element is failing or the temperature sensor (thermistor) is giving a false reading to the control board.
How to Fix It
Run a convection cycle at 400°F for 10 minutes. Carefully observe through the window. The heating element at the top rear of the cavity should glow bright orange consistently. If it's dim, cycles on/off rapidly, or doesn't glow, the element is faulty and needs replacement.
If That Didn't Work
If the element glows properly, the cavity temperature sensor is likely out of calibration or faulty. This requires a technician with the correct tools to diagnose and replace.
Heads Up
The interior light may stay off during a convection-only cycle. This is normal. Do not open the door frequently to check the element, as this causes large temperature swings and extends cooking time.