Guessed it must be either a heat sensor or a lower element. Bosch wall oven with no easy access to the back of the stove. Had to remove the door (very Heavy) to more easily access the temperature sensor. I thought from a video that the sensor could be easily replaced without having to access the red of the stove - not true! The sensor wire was secured to other wires and a clip screwed into the sheet metal. I was able to remove all screws with a Torx head driver. Since I had to pull the unit out and away from the wall enclosure I decided to replace the lower element anyway because the sensor tested just barely in speck by my ohm meter. After replacing the sensor and lower element the problem was fixed. I suspect that the sensor was at fault even though it tested in the lower range of being functional. Because the lower element was hidden under the stove floor and I already had to take the sheet metal off the back of the stove to free up the heat sensor it made sense to me to replace the element.
Bottomline - works great and I would have hated to see what an appliance repair person would have charged to travel 17 miles one way to do the repair and charged me.