It can be worrying - and not to mention inconvenient - if your car won’t start. But why do cars sometimes fail to start up?
Find out the top 10 reasons why you might have trouble starting your car. Plus, diagnose what that sound means when you turn the key, from a clicking noise to the engine cranking.
In this article:Why your car won’t start
Diagnose starting problems
Top reasons why cars won’t start
1. Flat, faulty or dead battery
The battery’s usually the main culprit behind issues with starting your car. In fact, battery problems were the cause in over half of the cases (55%) where our Patrols were called out to a car that wouldn’t start.*
There are a few ways your battery might go flat or even die:
- Something electrical was left on in the car, like the lights, which ran the battery down.
- You haven’t driven your car for a long time.
- A fault with one of the battery components.
If the car makes a rapid clicking sound when you turn the key but won’t start, it could be the battery. A jump start might get you going again but you may need to replace the battery or have a mechanic check it for problems and corrosion.
Battery problems are particularly likely to happen in cold weather, when the battery gets cold and struggles to hold its charge.
Dead car battery?
Battery Assist can help.
2. Starter motor problems
Almost 7% of the cars we see that won’t start have a problem with the starter motor.* The starter motor is connected to the car’s battery and sets the engine in motion when you start the ignition.
A symptom of a faulty starter motor might be a loud click when you try to turn the key in the ignition. If there’s a problem with the starter motor, a mechanic will need to check it along with the car’s electrical system.
3. Fuel problems
Fuel problems are responsible for around 1 in 20 (5%) of the cases where we’re called out to a car that won’t start.*
That includes issues with the fuel pump and electrical or mechanical issues with the fuel system.
4. Electrical or wiring problems
Nearly 5% of non-starting cars we attended had an electrical problem or an issue with the wiring.* These included issues with the fuse box, with battery cables or with the body control unit.
Remember that rodents can nest under the bonnet of your car and gnaw the wiring if it hasn’t been driven for a while.
5. Engine problems
Problems with the mechanics of your car’s engine can stop the car from starting. The main culprits are usually the crankshaft or the timing belt and timing chain. Altogether, they make up over 3% of non-starting cars we see.*
This could be the problem if the engine won’t turn over or starts and stalls.
6. Faulty immobilisers
Sometimes, you car’s security system might actually stop you from starting the car if it doesn’t recognise your key. This might be because the battery in your key fob’s low. Alarm and immobiliser issues make up nearly 3% of the breakdowns we see.*
Try holding your fob right against the start button or try a spare key. If it’s still not working or you don’t have a spare, you might need to get a new key.
7. Alternator problemsAlternator problems are responsible for over 2% of the cases where our mechanics attend a car that won’t start. They include issues with the alternator drive belt and the wiring.
The Alternator supplies the electricity needed to operate the lights, radio and heating. It also charges the car battery.
8. Engine intake issues
Problems with the engine intake include faulty fuel injectors, throttles, and fuel pressure regulators and sensors. If you struggle to start the car and have also noticed a whining or sputtering from the car recently, it could be a problem with the fuel system.
They make up more than 1% of the cars we go out to which won’t start.
9. Jammed ignition or steering lock
If you can’t turn the key in the ignition, the steering lock might be jammed. This happened to around 1,000 people between May and October 2020.*
This can be caused by a wheel pressing hard against a kerb or by parking with the steering wheel in full lock.
You can try these steps to free it up:
- You should be able to move the steering wheel slightly with the steering lock on.
- Try to find the free-play area by rocking the steering and see if the key will turn at this point.
- Sometimes it’s easier to do with 2 people.
- Don’t try to force the key or it may break.
You can often free a jammed lock yourself without needing a mechanic.
10. Spark plugs
Our mechanics see hundreds of cars every month that won’t start due to issues with the spark plugs.
A common issue is a flooded petrol engine. This happens when the engine’s switched off too soon after being started from cold. The unburned fuel which entered the engine remains there after you turn if off. That wets the spark plugs and makes it hard to restart the car.
It could be a flooded engine if you hear a very fast cranking sound when you turn the key (usually a 'whirring' sound). You might also notice a strong smell of petrol or the car may start briefly and cut out again.
11. Low AdBlue
If you’ve run out of AdBlue, you won’t be able to restart the engine. You may have to call out a mechanic as some car models need software to restart them.
It’s easy to avoid running out though - your car will show you a warning with a countdown on the dashboard to give you time to top up.
Diagnose starting problems
Sometimes you can get a clue about what’s wrong with your car from what happens when you try to start it.
No noise when starting the car
This could be a problem with your battery’s connection.
Rapid clicking noise when you start the ignition
This usually indicates a problem with the electrical system. It could be:
Single click when you start the ignition
This is usually a problem with the starter or starter relay (the switch which transmits power to the starter).
Engine cranks but car won’t start
This is often a fuel problem. It might be caused by:
Engine starts but cuts out
This could be caused by:
How to jump start your car
If you have trouble starting your car and think it’s a flat battery, you might be able to use a jump start to get you going again.
You’ll need to use a pair of jump leads to connect your battery to another car’s battery which is fully working.
Help for a breakdown at home
If your car won’t start at home, don’t keep turning the key for a long period of time as this could cause damage. It’s best to ask a mechanic for help.
With our At Home breakdown cover, we’ll come right to your doorstep and try to get you going again.
*Based on data from 112,580 non-starting vehicle breakdowns carried out by AA Patrols between May to August 2020.
These figures differ from comparable 2019 data due to the effect of COVID-19 on AA workloads. For example, battery-related problems accounted for 45% of breakdowns carried out by AA Patrols on non-starting vehicles over the same date range in 2019.