Serpentine Belt
A single, continuous belt that drives multiple engine accessories including the alternator, power steering pump, AC compressor, and water pump.
The serpentine belt is a single, long, continuous rubber belt that winds through multiple pulleys to drive several engine accessories simultaneously. Named for its snake-like path through the engine compartment, the serpentine belt typically powers the alternator, power steering pump, air conditioning compressor, water pump (on some engines), and occasionally other components like a secondary air injection pump.
Before the serpentine belt became standard in the late 1980s, vehicles used multiple individual V-belts to drive each accessory. The serpentine design simplified maintenance (one belt instead of several), improved reliability, and allowed for an automatic belt tensioner that maintains proper tension throughout the belt's life without manual adjustment.
Modern serpentine belts are made from EPDM (ethylene propylene diene monomer) rubber, which is more durable than the older neoprene belts but wears differently. Instead of cracking visibly, EPDM belts gradually lose material from the ribbed surface — similar to how a tire tread wears down. A worn belt may appear to be in good condition visually but slip on the pulleys due to rib wear. Mechanics use a belt wear gauge tool to measure rib depth and determine if replacement is needed.
A failing serpentine belt may produce squealing noises (especially on cold starts or during rain), and a broken belt will cause immediate loss of power steering, charging, and air conditioning. Most manufacturers recommend replacing the serpentine belt every 60,000 to 100,000 miles, along with the tensioner and idler pulleys.