Drive belt tensioners come in a variety of designs, but maintain one common goal, to keep the drive belt (or serpentine belt) tight and able to deal with the torque created by the crankshaft pulley, alternator, water pump, power steering pump, and other system components. A faulty tensioner may allow the belt to slacken, causing a loud squeal as the belts slip on the pulleys. This can manifest into a potentially dangerous situation if the belt were to come loose and fall off, losing all accessory power.