The alternator generates electricity to maintain sufficient power in the battery to both start the vehicle and run the electrical components such as the lights, stereo, electric windows etc.
In general they are very reliable, and trouble free. However, they can cause issues and may on occasion need repair or replacement.
Signs of a bad alternator
Often the first time you'll discover your alternator is bad is when either the battery goes flat (there are several causes of this, not just alternator failure) or when the battery light comes on the dashboard.
The ECU monitors the input to the battery and if it drops too low, the battery warning light will come on. If this is the case it could be caused by the alternator simply being worn out – the brushes which transmit the electricity from the 'stator' and to the rotor wear down over time, or it could be an issue with the electrical distribution system (whether than be the regulator or part of a 'smart charge' set up.)
With older alternators repair is usually straightforward, and with the component removed an auto-electrician can diagnose and rectify any issues, or a new alternator can be fitted.
Alternators on newer, more complex, cars require more sophisticated diagnosis, but due to their cost, repair is often preference to replacement. Testing the voltage output of the alternator is the primary method of diagnosing an issue with it.
The alternator can also appear to 'fail' if the aux belt snaps, or is very loose. You're also likely to suffer from power steering failure at the same time, so in the event of a snapped belt, it's usually immediately apparent it's happened.
How to extend the life of your alternator
There's not a great deal you can do to extend the life of the alternator, and failure if frequently sudden, rather than gradual – so you could have a perfectly functional alternator one day, and a dead one the next.
If you notice your headlights flickering, that could be warning sign however, as can a battery warning light that flickers, or stays on longer than usual when you start the car.
Keeping the engine components clean and free from dirt and debris is wise, and ensure that the aux belt is replaced as per the servicing schedule, and you should get many years of service from your alternator.
How long should an alternator last?
As alternators are generally trouble free – they can often last for the life of the car, and issues are usually rare on vehicles under 5 years old. Even though they're an incredibly hard-working component, it's not uncommon for them to reach 100,000 miles.
You're more likely to have an issue with the electrical side of things, as untimely the mechanics are very straightforward, with very few moving parts.
How much does it cost to replace an alternator yourself?
The actual alternator can cost from £50-£300 depending on the application, and fitting it can be as simple as removing a couple of bolts, or it can be a very involved process depending on how deep it's buried in the engine bay!
You'll not need anything other than a basic tool kit, and socket set – oh and use it as an opportunity to replace the aux belt at the same time. Our new Haynes OnDemand service will show you how to replace your car's alternator, as well as replace your auxiliary drivebelt!