A belt diagram is an illustration that shows a specific car's serpentine belt routing. The belt diagram is a reference used to assist in the replacement of the serpentine belt and is located under the hood of the car or in the owner's manual.
There are several different pulleys to choose from while installing a serpentine belt, making it possible to install the belt the wrong way. The diagram shows the correct routing for proper installation. If the belt diagram is faded or missing, online resources such as Serpentine Belt Diagrams provide belt diagrams for many different car models. The belt diagram varies based on the car model and year.