COMMON CAR BREAKDOWN CAUSES

We’ve been helping to keep drivers moving for more than 100 years.

Here we'll share with you what we’ve learned about the most common causes of breakdowns – and how to avoid them.

Flat or faulty battery

12 volt battery faults are the most common cause of breakdowns – especially in the winter, regardless whether you drive a petrol, diesel, electric or hybrid vehicle.

Flat batteries are commonly caused by a lack of use or too many short journeys. Faulty batteries or poor electrical connections can also create issues.

Batteries can go flat due to:

• Leaving your car unused for a while, or only used for short journeys
• A faulty component
• A problem with the car's charging system
• A fault with the battery itself
• Old age

How to avoid a flat battery

Don't forget to switch everything off as you leave the car. Removing the ignition key may not switch off the lights, but most modern cars have a 'lights on' warning sound as you open the car door.

If you don’t make long journeys very often, your battery won’t have much chance to charge. You can sort this out by charging it overnight every 2 weeks or so. We offer an easy-to-use Battery Maintainer you can buy online.

When your car's serviced, the garage should check that connections are secure and that the battery terminals are clean and protected from corrosion.

Also, most car batteries have a guarantee of 3 to 5 years, so you're living on borrowed time after then. Replace it before it lets you down.

We provide 24/7 roadside assistance.

Buy breakdown cover

Damaged tyres and wheels

Punctures, like flat batteries, are usually greeted with a groan. They're often caused by a sharp object, but other reasons include:

• The tyre's valve failing or getting damaged (where air is pumped in and let out)
• If the tyre's hit a kerb or a deep pothole
• The tyre and rim separating after a collision
• Old age (due to worn tyre tread, even if still legal)

If you hit a kerb or pothole, check your wheels and rims. Speak to a specialist tyre dealer ASAP if there's any damage. Discover how to claim for pothole damage here.

Looking for breakdown cover? Read about how it works:

• A complete guide to breakdown cover
• Family breakdown cover
• Multi-car breakdown cover

Changing a wheel

Replacing a flat tyre with the spare is normally straightforward. If you have a jack or other wheel removal tools, make sure they're in good condition and easy to get to.

If you have a spare wheel, it'll probably be in the car's boot (make sure the tyre's correctly inflated). Read our step-by-step guide on how to safely change a flat tyre.

Some cars come with a post-puncture sealant instead of a spare. The sealant is injected through the valve, but it's only designed to be a temporary repair.

How to avoid punctures

A few simple checks can help to prevent a breakdown from happening:

• Check your tyre tread depth and pressure regularly - including your spare wheel
• Check your tyre age and condition. Older, perished tyres are more prone to blow-outs
• Avoid driving over potholes or through puddles that could hide a pothole or damaged road surface
• If you spot uneven tyre wear, your wheels might be misaligned. Get a tyre centre or garage to check
• If you drive with heavy loads, adjust your tyre pressure to cope (you'll find this information in your handbook)

Engine oil

Having the wrong level of engine oil could damage your engine - and having too much oil is just as risky as having low oil.

If you drive a diesel with a DPF, the oil may become diluted if the DPF regeneration doesn't happen. This can cause serious engine damage and will need an oil change at your garage.

How to avoid an engine oil problem

• Regularly check your engine oil using the dipstick.
• The level should be between the two lines.
• The amount of oil between the bottom and top line of the dipstick is usually 1 litre.
• Your vehicle handbook will give you the correct oil specification.

Timing belt or chain

Timing belts (or chains depending on engine design) are critical components. If a timing belt or chain fails, catastrophic damage will almost certainly occur.

Regular servicing can help to avoid issues with timing belts and chains. Belts have a limited service life and will need to be changed according to the manufacturers recommended mileage or time intervals, whichever comes first. While this can be expensive, it will save a more costly breakdown later on.

Lack of oil, or oil degradation are the main reasons for timing chain failure. Regular oil changes, and keeping the engine oil at the correct level will increase the lifespan of your timing chain.

How to avoid a timing belt/chain failure

• If your engine has a timing belt, your garage should check it during the service, and will advise when it needs to be changed
• Keep your engine oil topped up, and changed regularly
• Listen for engine noise. Worn belts can make a loud rubbing or drumming sound when they're worn. 
• Worn or stretched timing chains make a loud rattling sound.
• Consult your garage if you hear any unusual sounds from your engine

Need a service?

Our AA Smart Care team can book you into one of over 650 AA approved garages who can look after all your servicing and MOT requirements.

Diesel Particulate Filter (DPF)

This is a part of the exhaust system on diesel engine vehicles. It traps fine particles of soot and burns them off into less-harmful gas (a process called regeneration).

The Diesel Particular Filter should look after itself, but it may get blocked up if you do lots of short journeys.

How to prevent a clogged DPF

• A weekly run up the motorway should stop it from blocking.
• If it does get overloaded, a warning light will come on the dashboard.
• If the warning light's on, you'll need to drive at motorway speeds for a decent period to clear it.
• Full instructions should be in the vehicle handbook.

Alternator faults

If you’re experiencing persistent battery problems and dim headlights when your engine is idling, you could have a fault with your alternator. Call us out on 0800 77 66 55, or give your garage a ring as soon as you can.

If your ignition warning light comes on and the engine temperature rises quickly, the belt that drives the alternator and water pump could have broken.This is a serious problem.

Stop right away and give us a call on 0800 77 66 55. Do not restart your engine.

Fuel problems

Wrong fuel

Put the wrong fuel in your engine? It happens to around 133,000 drivers every year.

Don’t start your engine if you've put petrol in a diesel or vice versa. Just push your car off the forecourt to a safe place and call our Fuel Assist team.

How to avoid using the wrong fuel

It's an easy mistake to make, so double-check the pump nozzle before you pull the trigger:

• Green for petrol
• Black for diesel

The diesel nozzle is also larger, so it can be harder to mis-fill a petrol vehicle.

Running out of fuel

Running out is another fuel problem drivers call us out for - and often the one they feel most embarrassed about! When the needle goes on the red (or bleeps), it can be easy to overestimate how much fuel is still left in the tank.

How to avoid running out of fuel

It's best not to rely on your car's display which shows how many miles are left until the tank's empty. It's not always accurate.

If your tank's low:

• Fill it up sooner rather than later
• Top up the day before a long journey

Of course, our breakdown mechanics are always on-hand to give you a top up if you need a few litres to get moving again.

Engine flooded with fuel

If it's cold and you stop your car too quickly after starting it, your engine could become flooded with petrol. Luckily it's usually simple to fix a flooded petrol engine.

How to avoid flooding your engine

If you drive a petrol car, give the engine time to warm up once it’s been started from cold. This only takes a few minutes. When it’s warm enough, the engine note changes and the idle speed drops slightly.

Overheating

Overheating can be a top cause of breakdowns. If your temperature warning light's on, there could be problem with the engine or with the cooling system.

If there's steam coming from your engine or the temperature warning light's on, pull over in the nearest safe spot and call us.

How to avoid overheating

Make sure you regularly check and top up your coolant. You can also check your car's cooling fan at the same time.

Check for leaks if you notice the coolant level has dropped. Modern cooling systems shouldn't really need topping-up between services, so it's best to get a garage to check it out.

Lost keys

If you lose your key or lock it inside your car, you're going to need help to get back in. Keeping a spare car key at home is a good idea, but little use if you're far away.

Your key most likely includes a microchip, designed to stop your car being stolen, which can make it harder to replace if you lose it. That's why lost or trapped keys are a big cause of breakdowns.

You'll either need to visit an authorised dealer or to call someone qualified out to your car to help you.

We offer a special Key Assist service which can programme a new key for almost any vehicle.