Car Won’t Start in the Cold? Causes and What to Do

Car slow to start or dead on a cold morning? Why cold weather hits batteries and diesels, what to try safely, and how to stop it happening again.

The first cold snap of the year is when many cars that started fine all summer suddenly won't. The engine turns over slowly, clicks, or does nothing at all, usually when you are already late. Cold weather rarely causes the fault on its own. It exposes a battery, starter or fuel problem that was already there. This guide explains why cars struggle to start in the cold, how to work out what's wrong from the sound it makes, what you can safely try, and how to stop it happening again.

Quick answer: why won't my car start in the cold?

• A weak battery. A battery delivers less power when it's cold, just when the engine needs more to turn over. An older battery that coped in summer may not cope on a frosty morning.
• Thicker engine oil. Cold oil is thicker, so the engine is harder to turn and the starter motor draws more current from the battery.
• Short trips. Winter driving uses lights, heater, fan and heated screens, and a short journey may not put back the charge used to start the car.
• Diesel glow plugs or fuel. Diesels rely on glow plugs to start from cold, and diesel fuel can thicken in severe cold.
• A failing starter motor, alternator or connection that finally gives up when the load is highest.

Work out what's wrong from the sound

• Slow, labouring crank that gradually gets slower: most likely a weak or flat battery, or a poor connection at the terminals.
• Rapid clicking: the battery doesn't have enough charge to turn the starter motor. Our guide on why a car clicks but won't start goes into more detail.
• A single click with bright dashboard lights: the battery may be fine, and the problem may be the starter motor, its solenoid or a connection.
• Nothing at all, with no dashboard lights: a completely flat battery, a loose or corroded terminal, or a main fuse.
• The engine cranks normally but won't fire: more likely fuel, ignition, glow plugs (on a diesel) or the immobiliser than the battery.
• Key not recognised or a flashing immobiliser light: the battery in your key fob may be weak, and cold makes it worse. Your handbook shows the backup way to start the car with a flat key battery.

What to try when your car won't start in the cold

1. Switch everything off first

Turn off the heater fan, heated screens, lights, radio and anything plugged in, so all the battery's power goes to the starter motor.

2. Press the clutch on a manual car

Many handbooks recommend pressing the clutch while you start a manual car, which reduces the load on the starter. Many modern cars won't start without it anyway.

3. On a diesel, wait for the glow plug light

Turn the key to the position before starting (or press the start button without pressing the brake or clutch, depending on your car) and wait for the coil-shaped glow plug light on the dashboard to go out. Then start the engine. Starting before the plugs have warmed the cylinders makes a cold start much harder.

4. Crank in short bursts

Don't hold the key on and keep cranking. Try for a few seconds, then pause for half a minute or so to let the battery recover and stop the starter motor overheating. If the car hasn't started after a few attempts, stop: more cranking will flatten the battery completely.

5. Check the battery terminals

A loose clamp or a crust of white or green corrosion can stop the current getting through, and cold makes a poor connection worse. Our guide to car battery terminal corrosion explains how to check and clean them safely.

6. Jump start safely, or use a booster pack

Follow your handbook, because many cars have special jump-start points under the bonnet, and hybrids and some other models have their own instructions. The usual order is:

1. Red lead to the positive (+) terminal of the flat battery.
2. Other end of the red lead to the positive (+) terminal of the good battery.
3. Black lead to the negative (−) terminal of the good battery.
4. Other end of the black lead to a bare metal earth point on the car with the flat battery, away from the battery.
5. Start the car with the good battery, let it run for a few minutes, then start your car.
6. Remove the leads in the reverse order.

Never try to jump start a battery that is cracked, leaking or swollen. If you're not confident, ask a professional, and if you're stuck at the roadside, call your breakdown provider.

7. Get the battery tested once it starts

A car that needed a jump this morning will very likely need one tomorrow. A short drive won't fully recharge a flat battery, and if the battery is weak or the alternator isn't charging properly, the problem will come back. A battery and charging system test tells you which.

Cold-weather problems on diesel cars

• Glow plugs: if one or more has failed, the engine may crank for a long time, start roughly or smoke on cold mornings, then run normally once warm.
• Fuel waxing: in severe cold, diesel can start to thicken and block the fuel filter. UK filling stations supply a winter grade of diesel in the colder months that is designed to flow at lower temperatures, but a car left standing in a hard frost can still be affected. A fuel filter that is due for replacement makes it more likely.
• A weak battery: diesels need more power to start than most petrol engines, so a tired battery shows up sooner.

Other causes that show up in winter

• An alternator that isn't charging properly. If the battery warning light comes on while driving, or the battery goes flat again after charging, the alternator may be at fault. See what a car alternator does.
• Something draining the battery when the car is parked, such as a light left on or a faulty module. Our guide on why a car battery keeps going flat covers the usual causes.
• The wrong battery on a start-stop car. Start-stop cars need a specific type of battery, often AGM or EFB, and some need it registered to the car after fitting. See start-stop battery replacement.
• An old battery. Many car batteries last around four to five years, less if the car does mostly short trips or sits unused for long periods.

How to stop it happening again

• Get your battery tested before the coldest weeks, especially if it's more than four years old or the car has been slow to start.
• Replace a weak battery before it leaves you stuck. Our signs your car battery needs replacing guide lists the warning signs.
• Drive for longer now and then, or use a smart battery charger if the car is left unused for weeks.
• Use the right engine oil for your car. Oil that doesn't meet the manufacturer's specification can make cold starts harder.
• Keep up with servicing. Filters, glow plugs and spark plugs are checked or replaced at the intervals your car needs, and our winter car service checklist covers the rest.

Will a weak battery affect your MOT?

The MOT doesn't test how healthy your battery is, but a battery that is insecure and likely to fall or cause a short circuit, or one that is leaking, is a major defect. A weak battery can also bring on warning lights, such as the airbag or stability control lights, and some of those are MOT fails if they show a fault. If you're looking for an MOT near me, you can book your MOT online at an approved MOT test centre, discounted when you book it with a service.

How Hon Car Service can help

Hon Car Service is an online booking platform for car servicing, MOTs and repairs across the UK. Enter your car registration and postcode for an instant fixed price on a battery test or replacement, a starter motor or alternator replacement, or a winter service, with parts and labour included. If your car won't start at home, a mobile mechanic can come to your home or work at a time you book, or choose free collection and return or a trusted local garage. Your card is pre-authorised when you book and only charged after the work is done and approved, and every job comes with a 12-month parts and labour warranty.

FAQs

Why does my car struggle to start when it's cold?

A battery delivers less power when it's cold, and cold, thick oil makes the engine harder to turn, so the starter motor needs more power just when less is available. A battery that is old or not fully charged often can't cope, which is why problems show up on the first frosty mornings.

How long should I crank the engine before stopping?

Only a few seconds at a time, with a pause of around half a minute between attempts. If it hasn't started after a few tries, stop, because continued cranking flattens the battery and can overheat the starter motor.

Can cold weather kill a car battery?

Cold weather usually exposes a battery that was already weak rather than killing a healthy one. If your car is slow to start in the cold, get the battery and charging system tested before it fails completely.

Should I let the engine idle to warm up?

Modern engines don't need a long warm-up. Once the windows are clear, drive off gently and avoid high revs until the engine is warm. On a public road you must not leave the engine running unnecessarily while stationary (Highway Code rule 123).

How do I know if it's the battery or the starter motor?

A slow crank or rapid clicking usually points to the battery. A single click with bright dashboard lights, or a car that won't crank even after a good jump start, points more towards the starter motor or a connection. A mechanic can test both.

Can a mobile mechanic replace my battery at home?

Yes. Book a battery replacement online and a mobile mechanic can fit it at your home or work. If you'd rather use a garage near you, you can choose a trusted local garage or free collection and return instead.