Many car owners confuse a serpentine belt with the timing belt, but the two serve different purposes. In a nutshell, a timing belt keeps the camshaft and crankshaft in sync, regulating the “timing” of the opening and closing of the valves with the up-and-down motion of the pistons. It is also concealed from view by a cover that attaches to the engine block.
A serpentine belt, on the other hand, is so called because it’s long, snake-like movements transmit mechanical power to several very important engine accessories including the water pump, power steering pump, alternator, air and oil pumps, and the A/C compressor. You can see this belt when you lift the hood of your car.
The question remains: Why do I need to replace my serpentine belt? Because a bad or failing serpentine belt will cause your engine to overheat and eventually stop running. The good news is — as far as engine repairs go — serpentine belts are fairly inexpensive to replace.