A typical serpentine belt tensioner has two major components. • A bearing mounted pulley • A spring mounted arm Symptoms will depend on the part that fails. For instance, if the spring breaks, the belt will not be held tight. In this case symptoms will range from a squealing noise to the belt coming off. When the pulley and/or bearing goes bad, there will normally be a squeak, roar or rumbling noise. When the pulley bearing fails, it may seize. This will cause severe squealing and even smoke. When the pulley or arm breaks, the belt will be thrown off, causing the accessories being driven to stop operating. For more information on belts, see our Detailed Topics article, About Serpentine Belts.