There is an important part in the drive belt named idler pulley. The drive belt is held by the idler pulley, which keeps the tension on the drive belt and guides it. Simply, the idler pulley is designed to maintain and guide the tension with the drive belt. However, owing to a longtime heat, friction, tension and deterioration, your idler pulley will be worn one day. If you hear some strange sound from the engine when you are driving; if the Warning light in the panel in on; if there is a loss of power steering; if your car is overheating, you are supposed to check your idler pulley immediately and replace it if it's needed. Comparing to the expensive labor cost in the store, you can save your money by ordering a BMW genuine OEM idler pulley with a discounted price here and change it by yourself.