Signs of a faulty alternator – all you need to know

When it comes to car maintenance, having an alternator in full working condition is vitally important.

A key part of your vehicle's electrical system, the alternator converts mechanical energy into electricity to power your vehicle's accessories and systems. Wear and tear, faults, damage and exposure to the elements can all result in alternator problems or failure. 

Here, we outline common alternator problems, if it can be repaired and the cost to replace one if it fails. 

What is an alternator?

An alternator is a critical component that generates electrical power to keep the vehicle's battery charged, while also supplying electricity to the car's various electrical systems.

As the engine runs, it drives the alternator via a belt and a spinning rotor. This generates an electrical current which is what the vehicle’s electrical system uses. The alternator also keeps the car battery charged while the engine is running.

It is essential as this ensures that the engine has enough power to start the vehicle and operate electrical components like warning lights, indicators, entertainment systems and air conditioning.

Regular maintenance and services can help keep an alternator functioning properly.

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Signs of a broken alternator

The most obvious indicator of an alternator issue is a dashboard warning light. This is often a yellow light, shaped like a battery.

However, there are several other likely signs, including headlights or interior lights appearing dimmer than before or flickering on and off. When the car is idling, it will be easy to spot this.

Further electrical issues include windows, air conditioning or the entertainment system not working correctly.

Frequent dead batteries or difficulty starting the engine can also indicate alternator problems – as well as more serious problems within the engine itself.

When a driver is traveling at speed, they may also notice a loud grinding noise coming from the engine.

This can then be followed by a smell of burning rubber and the engine stalling unexpectedly.

If you notice any of these signs, it’s advisable to have the alternator checked by a trusted local garage or by a mobile mechanic.

Can you repair an alternator?

Yes, an alternator can often be repaired, depending on the type and extent of the damage.

It is important to note that in most cases this should be carried out by an experienced mechanic with the correct equipment.

However, there are some more simple fixes that can be conducted at home.

If the bearings are worn or noisy, they can be replaced.

Similarly, damaged or frayed wiring can sometimes be repaired without replacing the entire alternator.

And in some cases, just cleaning dirt and debris can help improve the functionality of the alternator and the linked components.

If these don’t fix the problem, then you’ll either need to get it replaced or some alternators can be rebuilt by replacing internal components.

In most cases, it may be more cost-effective to replace the alternator.

Alternator replacement cost

When it comes to paying for a replacement alternator, drivers in the UK can expect to pay anywhere from £250 to £800.

However, this can be significantly higher depending on the level of damage to the surrounding area – as well as the make, model, age, and condition of the vehicle.

The average price for parts and labour is around £438.

It is worth noting that alternators can be one of the more expensive parts of vehicle to fix or replace.

^{Source: WhoFixMyCar, May 2025}