Quick answer: Automatic litter box odor usually comes from an overfull waste drawer, infrequent cleaning, the wrong litter type, or a rake leaving residue in the main chamber.
Even with a sealed waste drawer, decomposing waste produces ammonia and sulfur compounds that seep out around the edges. Empty it at least twice a week, more in warm weather or with multiple cats. An odor-absorbing liner or carbon filter insert in the drawer helps significantly.
Low-quality or lightweight litters leave residue that breaks up and contaminates clean litter over time. Upgrade to a high-quality clumping litter with activated charcoal or baking soda. Avoid scented litters — strong fragrances mask odor temporarily but deter cats from using the box.
If the rake isn't clearing waste completely, residue builds up in the litter bed and causes persistent odor. Check that the rake mechanism moves freely and that litter depth is within the manufacturer's recommended range — too much or too little litter causes incomplete cycles.
Most automatic litter box odors are maintenance issues, not equipment failures. More frequent drawer emptying and better litter quality resolve the majority of cases.