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Cars with combustion engines burn petrol or diesel to pile on the miles, but they can't go anywhere without electricity, and the alternator generates that electricity by charging the 12v/24v battery.
Alternators convert mechanical energy from the engine into electrical energy by turning a drive belt connected to the alternator pulley, which spins the alternator's rotor to provide the volt flow necessary to recharge the battery.
Problems with a car alternator can spell disaster for the delicate balance of mechanical energy and electricity, although these components don't usually just go bang—there are tell-tale signs that something is amok.
Failing Car Alternator Symptoms
Warning light on the dash
Your car will hint that the alternator is failing by showing the battery warning light on your dashboard.
Either your battery isn't charging, or another component has a problem – the alternator or something as simple as a loose wire.
You need to get into a reputable garage for a fault code read to determine what's up and resolve the problem.
High-pitched squealing
The alternator is driven by a belt connected to the engine's crankshaft, and if this belt becomes loose, worn, or damaged, it can slip on the alternator pulley, causing a squealing noise that pierces the ears like the best catfights.
A slipping belt sounds atrocious, and it also means it's under stress. Should it snap, you might lose power steering (this runs off the alternator in most cars), and the water pump might stop working, overheating your engine.
The solution is to have a garage install a new alternator belt.
Difficulty starting
When you press the start engine button or turn the key in the ignition, the engine should explode into life and tick over. A bad alternator will stop this from happening, and there are a few signs it might be the reason why:
- Intermittent starts where it bursts into life only sometimes.
- Clicking sounds when trying to start the engine.
- Extended cranking time where it starts but takes several seconds.
It's very possible for this problem to leave you stranded, so if you have trouble starting, get your car into a garage as soon as you can.
Battery problems
A healthy battery will start your car quickly and hold a charge for ages, so you might call out the battery as a rotten egg when it doesn't do these things. But what if it's the alternator?
Alternators can fail to charge a battery when the belt spins off-axis on the pulley or when internal components like the rotor, stator, and bearings wear out over time.
The bottom line: an inability to hold a charge or deliver power might not be the battery's fault, and only a garage can help determine it.
How Serious Are Alternator Problems?
Alternator problems can impact your life by leaving you stranded and without a car for several days. Should your car not start and need towing, you're at the mercy of the repair timeline of the garage you land at.
Some people get by just fine with a squealing alternator belt, merrily ignoring the stress it's under to save, skip the garage bill and inconvenience. But trust us – that belt needs replacing because it's an inefficient cog in the system.
In a worst-case scenario, you might get:
- Engine damage from overheating because the alternator powers the belt-driven water pump in most cars.
- Other damage from belt-driven components not working.
- A dangerous loss in power steering that renders the car undrivable – particularly dangerous at motorway speeds.
- High-voltage transfer that blows out electricals—while circuit breakers will save the ECU and other major components, sensors and smaller components can be damaged by overvoltage from the alternator.
How Much Does Repair Cost?
Alternator replacement
Alternators and pulley systems aren't particularly expensive components, although they only make up around 40% of the bill—most of it is labour and taxes, so it pays to shop around for a fair garage.
Most alternator replacements cost between £450 and £600, including the alternator, pulley system, and labour.
Expect to pay an enormous premium through marque dealerships and well-known repair shop chains. Independent garages are usually more affordable, and if you can find a brand specialist, all the better for quality's sake.
Alternator belt replacement
You'll pay between £150 and £250 for a reputable garage to replace your alternator belt and an additional 20% if you go through a dealer.
A quick Google search reveals that alternator belts cost less than £30, but the professional installation adds to the cost. Unless you are a mechanic, you can't safely replace this component at home.
Summing Up
Car alternator problems rarely spell the end of the road, but they can massively inconvenience you and lead to worse problems like engine overheating and overvoltage to sensitive low-voltage electrical components.
If you suspect alternator problems, diagnosis is as easy as asking a reputable garage to examine the vehicle with a fault code reader and run some tests.
Professional diagnosis is critical because some symptoms, like voltage issues and battery lights on the dashboard, can signify problems with the battery, sensors, or fuses separate from the alternator. The last thing you want is an expensive alternator repair when the only fix you really need is a new battery or sensor.
Most alternators last six to eight years or up to 150,000 miles before going bad, although the belt usually needs changing somewhere in between.
Older cars are at a higher risk of alternator problems - get your garage to inspect the alternator's performance during your service and pay close attention to how your car starts to keep ahead of any problems.