I just noticed today that my four year old frigerator is not making ice. I have the side by side with the ice maker in the door. I was wondering if it was the sensor or the whole ice maker is shot?

They have had a lot of problems with the ones with the ice bucket on the door.
The sensor normally does not go bad.
The fill tube (the water line that goes from the back of the freezer to the ice maker) could be frozen. Two reasons for that.
1- the water valve has a slow drip to it and the drips freeze and slowly ice up the tube. The fix is to replace the water valve and thaw the line with a hair drier.
2- thin insulation around the fill tube where it travels over the freezer compartment. WHP makes a small heater that slides inside it for a correction

If the fill tube is not frozen then its either a bad ice maker or water valve