The self-cleaning function of an oven is not so reliable. Therefore, it would be best to use a safe, natural, and super effective method to get the job done. You could be dealing with some elbow grease, but will that be worth the trouble?
Mix a 1/2 cup of baking soda with a few tablespoons of water to have a spreadable paste. Simply coat the oven's interior surfaces with the paste and let it sit overnight. Clean the oven with a damp cloth and spray a little vinegar over baking soda residue. Take a wet cloth and clean the oven. Voila! All clean.