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.
1. Flat or faulty battery
Battery faults are the most common cause of breakdowns – especially in the winter.
If you’ve got a problem with your battery, you might not be able to start your car. A car's battery powers the starter motor, and then the engine turns the alternator, which recharges the battery.
Flat batteries are commonly caused by leaving the lights on when the engine's off. But there’s also a good chance battery problems will be down to lots of short journeys or a poor electrical connection.
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.
Call us out on 0800 77 66 55. Our breakdown mechanics will:
They'll then charge your battery, or replace it if required, so you can carry on your journey.
2. 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.
3. 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.
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 tyre, it'll probably be in the car's boot (make sure it'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.
- If you spot uneven tyre wear, your wheels might be misaligned. Get a tyre centre or garage to check.
- If you’re drive with heavy loads, adjust your tyre pressure to cope (you'll find this information in your handbook).
- Avoid driving over potholes or through puddles that could hide a pothole or damaged road surface.
Most modern diesel vehicles use Selective Catalyst Reduction (SCR) which lowers harmful nitrogen oxide (NOx) emissions from the exhaust. AdBlue is an additive that helps with this. It's sometimes called urea or Diesel Exhaust Fluid (DEF), and it needs to be kept topped up to work properly.
Your handbook will tell you where the filler is and how much to use. Plus there's a mileage countdown display on the dashboard that'll warn you about how far you can drive on what's left. Your engine won't start if it runs out, so it’s important to keep it topped up.
How to avoid AdBlue problems
- Top up your AdBlue levels regularly.
- Keep an eye on the mileage countdown to make sure it doesn't run out.
- Take care not to mix up the AdBlue tank and fuel tank when refilling.
5. 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.
6. 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.
7. 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.
8. Starter motor
Although starter motors are usually tough and robust, they do fail eventually.
As long as you get your car serviced regularly, any potential faults should be picked up before they cause you any problems.
9. Fuel problems
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.
Filled up with the wrong 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.
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
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.
Published: 29 March 2016 | Updated:10 January 2020 | Author: The AA