What is a Serpentine Belt?
The long ribbed belt that drives your alternator, power steering and air-con.
Simplified animation — not to scale.
In plain English
Also called the auxiliary or "aux" belt, the serpentine belt is a single long rubber belt that snakes around several pulleys on the front of the engine. It powers accessories like the alternator, power steering pump, water pump and air-conditioning compressor.
"Like the elastic band driving a row of spinning tops — when it breaks, every accessory stops at once."
How it works
The engine's crankshaft pulley spins the belt; the belt spins everything else. A spring-loaded tensioner keeps it tight. If it snaps or slips, you lose charging, power steering and often cooling all at once — you'll usually have minutes, not hours, before the engine overheats.
Signs of trouble
- ⚠Squealing or chirping from the front of the engine
- ⚠Visible cracks, fraying or glazing on the belt
- ⚠Battery warning light combined with stiff steering
- ⚠Engine overheating shortly after start-up
- ⚠Power steering suddenly heavy
£90–£200 fitted
Always get a written quote. Prices vary by car, region, and parts brand.