Your vehicle’s alternator is a power generator in charge of keeping the battery charged and powering the different electrical components in your ride. The alternator belt is what drives the alternator, making it essential for various parts of your vehicle’s electrical system.
The alternator belt used to be a separate V-belt solely dedicated to driving the alternator. In newer vehicles, it’s been replaced by a serpentine belt that drives multiple units throughout the vehicle, including the alternator, power steering pump, water pump, and air pulleys. If your alternator or serpentine belt is damaged, you may notice the following symptoms:
Bad Alternator Belt Symptoms
Squealing Belt Noises
A bad or loose alternator belt will tend to flap around since it won’t be properly seated in the system. This flapping can lead to squealing noises while your vehicle is running, especially in cold weather. The noise is likely one of the things you’ll notice first with a problematic alternator band. Alternatively, a weak tensioner might also be what’s causing the noise.
Weak or Dead Battery
Because the alternator keeps the battery charged, a problem with the alternator belt means your battery performance will decline. You might notice that the battery is either weak or completely dead, leading to a vehicle that’s difficult to start or an engine that cranks slowly.
Battery Warning Light
Related to a weak or dead battery, your vehicle’s battery warning light might turn on. This is an indicator that there’s something wrong with your vehicle’s electrical system. A bad alternator belt may trigger this since it can’t keep the battery charged.
Flickering or Dimming Lights
If your alternator can’t keep the battery charged because of a faulty alternator belt, you’ll notice the lights of your vehicle flicker or dim as you drive. Both interior and exterior lights will be affected by the loss of power.
Electrical Issues
You might notice your car’s other electrical components begin to malfunction as well. A failing alternator belt leads to your battery being unable to power all the different electronics effectively. Your radio or infotainment might shut down periodically, and your automatic windows might be sluggish while operating.
Stalling or Failing Engine
If your vehicle’s battery starts to fail while your engine is running thanks to a bad alternator band, it can start to affect the fuel injectors. The fuel injectors require electricity to function, and they will misfire if the electricity isn’t immediately available. You could also start to have driveability issues due to low battery voltage, and overheating might result from the cooling fans demanding a lot of electrical current.
Burning Smell
A bad alternator belt might cause excess friction while in operation. As the heat builds up from the friction, it’ll give off a burning rubber smell, which is similar to the scent of an electrical fire. This happens if the belt is slipping on its pulley, which can cause your alternator to output lower amounts of power.
Squealing Noise
On older vehicles, a loose alternator belt will cause a high-pitched noise when starting the engine while it’s cold. As the engine warms up, the sound will start to fade. This happens because the alternator belt is more slippery when it’s cold, which makes it slip on the alternator. If the belt is very loose, the high-pitched noise might become constant.
When Should You Replace Your Alternator Belt?
An older V-belt alternator band can last up to 4 years or 40,000 miles before it fails. Serpentine belts, on the other hand, should be good for anywhere between 60,000 to 100,000 miles. Ethylene propylene diene monomer (EPDM) belts are especially durable and can last up to 10 years.
That being said, belts still degrade and may get problematic when they reach their threshold. Belts can begin to fray and peel or become loose and misaligned before they completely fail. You’ll also usually see slight cracking between the grooves on the inside of an old serpentine belt, indicating that it needs to be replaced soon. Now that you know what a loose alternator belt can cause, you’re more able to gauge if your vehicle needs a new one.
Usually with serpentine belts, aside from fraying due to an alignment issue or something damaging the belt, you will start to see slight cracking in between the grooves on the inside of the belt. Once you start to see that, replace the belt soon.
–Anthony Harlin, ASE Certified Master Automobile Technician
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