Noises
Belt squeal when starting or turning: what it means
A high-pitched squeal on a cold start, at full steering lock or when switching on the air conditioning is usually the auxiliary drive belt slipping on a pulley. It normally means a worn belt, a weak tensioner or a pulley with a damaged bearing.
See a garage soonNoises
Reviewed by Daniel Morales, founder of Reprorace SL, on
Is it serious? Can I keep driving?
Carefully, and only as far as the garage. You can drive to the garage, but do not leave it: if the belt breaks, the alternator stops charging and on many cars the water pump or power steering stop too. If the battery or temperature light comes on, stop as soon as it is safe.
A careful, general answer: only someone who inspects the car can say whether it is safe to drive. When in doubt, stop somewhere safe and call for assistance.
Most likely causes
- Worn or glazed belt: it loses grip with time and heat.
- Tensioner or idler pulley: a weak tensioner or a damaged bearing makes the belt slip or flutter.
- Contamination: oil or coolant on the belt makes it slip.
- Stiff accessory: an air-conditioning compressor or an alternator that drags overloads the belt.
Listed from more to less common in general; on your car they may be different. A fault-code reading and a check at the garage confirm which one it is.
To understand it better: How can you tell if the 12 V battery is failing? How often should you run diagnostics on your car?
Car system: Electrical system and battery
What you can check yourself
Note when it squeals: when cold, in damp weather, when turning the wheel or switching on the air conditioning.
With the engine off and cold, look at the belt: cracks, missing chunks or frayed edges.
Do not spray products on the belt: they can silence it for a while and damage it.
Never touch the belt or pulleys with the engine running.
Safe checks only: with the engine off and cold whenever you look under the hood, without taking anything apart and without touching hot or moving parts.
Related fault codes
Generic codes that often come with this symptom. Seeing one does not confirm the cause: it is where the diagnosis starts.
How the ECO-LITE helps diagnose it
Plugged into the OBD socket, the ECO-LITE reads the fault codes of the control units that answer, with the freeze-frame data captured when the fault happened, and shows live data on your phone or computer. With your permission, your garage can see them remotely before you bring the car in.
What to look at here: system voltage with the engine running and as loads switch on: if it drops, the alternator is not being driven properly.
Frequently asked questions
Is it the timing belt?
Almost never: the timing belt is covered and does not usually squeal. The squeal is the auxiliary belt, the one that drives the alternator, pump and compressor.
Why does it only squeal in damp weather?
Moisture reduces the grip of a belt that is already a little worn or loose. It is a reminder to have it checked.
Is only the belt replaced?
It often pays to replace the tensioner or pulley too if they are worn; otherwise the noise comes back.
Keep reading
- Electrical system and battery: how it works and what fails
- Battery warning light on: what it means and what to do
- Heavy steering or steering warning light on: what to do
- Engine temperature warning light on: what to do
- Car symptoms: what they mean and what to do
- Check engine light on: what to do
- How to read and clear your car's fault codes
- OBD fault codes: what each one means