What Car Warning Lights Mean

When you switch your car on, the last thing you want to see on the dashboard is one of those dreaded warning lights staring back at you. Some are easy to understand; others, less so.

It's easy to panic and misinterpret what the little symbol means. That's why we've created this guide, which will help you confidently identify standard warning lights and understand what they are trying to communicate.

Airbag warning light

What it looks like: incoming beach ball attack.

When this light comes on, it can mean two things:

• Your airbag is faulty and won’t deploy in an accident.

• Your airbag could deploy at any moment and cause an injury.

Possible causes

A few things can trigger the airbag warning light. Check out this guide for a full explanation of why it can come on and how to fix it.

1. A faulty sensor

Sensors are usually designed to last the lifetime of a car, but they're not perfect. If the airbag sensor develops a fault, it will trigger the appropriate warning light. Similarly, sensors may need to be repaired or replaced following a collision.

2. Electrical issues

Loose wires in the electrical system could be to blame.

3. Faulty seatbelt pretensioners

Pretensioners are responsible for tightening the seatbelts during a collision. Like airbags, they are part of the supplemental restraint system (SRS); when they fail, they can trigger the airbag warning light.

Engine management light

What it looks like: a missing jigsaw piece.

The engine management light may appear yellow, flashing yellow, or red in colour. A red light is serious and indicates you should stop driving and contact a mechanic. A yellow light indicates a less severe problem, though it still requires attention.

Possible causes

Unfortunately, this is one of the most tricky warning lights to diagnose because it can indicate a wide array of issues.

1. Malfunctioning oxygen sensor

The oxygen sensor measures the amount of unburnt fuel in the engine. When it fails, more fuel is burnt than needed, causing a drastic decrease in efficiency. You can keep driving until you reach your destination, but you should have the sensor fixed as soon as possible.

2. Faulty spark plugs

When a spark plug or its wiring fails, you will notice a drop in your car's efficiency. This guide discusses other signs that your spark plugs need replacing.

Find out how to do the job yourself here, or if you don't feel confident, contact one of our friendly mechanics.

3. Blocked EGR valve

The exhaust gas recirculation (EGR) valve helps to lower emissions. In diesel cars, it is prone to blockages due to built up carbon deposits, which are created when the vehicle does too many short journeys. The valve needs cleaning or replacing, after which you can reset the warning light.

Brake warning light

What it looks like: Princess Leia is in trouble.

This light comes on when there is a problem with your brakes, which means you need to be careful bringing the car to a halt.

Possible causes

1. Low brake fluid

The most likely reason this warning light has come on is low brake fluid. Fortunately, this is an issue you can resolve yourself - this guide explains how to locate the fluid reservoir and top it up.

2. Brake fluid leak

Brake fluid needs topping up occasionally - this is perfectly normal. However, you should always check whether there is a leak in the system causing the low fluid level.

Driving with a brake fluid leak is dangerous; you don't know how long your brakes will continue working, so you shouldn't delay booking a repair.

3. Failed hydraulic circuits

Your brake pedal will likely feel spongy if this is the cause.

4. Overly worn brake pads

Ignoring the signs that your brake pads need replacing may eventually lead to the brake warning light appearing on your dashboard. Find out how much it costs to replace brake pads here.

5. Sensor failure

A faulty sensor can trigger the brake warning light erroneously. In this case, the sensor needs replacing, rather than a brake component.

Power steering

What it looks like: The peace symbol needs repairing.

When the power steering warning light comes on, you may already know the issue because of how your car is handling; the steering wheel may suddenly feel stiffer, and the vehicle may be more challenging to manoeuvre.

Possible causes

1. Power steering fluid leak

Power steering fluid provides a hydraulic link between the car's front wheels and the steering wheel. When the system has a leak, it will be considerably harder - though not impossible - to turn the car.

This is by far the most likely reason for the power steering dashboard light.

Diesel particulate filter

What it looks like: All my eggs are in one basket.

This warning light signals a problem with the diesel particulate filter (DPF).

Possible causes

1. Clogged DPF

The DPF is designed to regenerate (clean itself) using heat to burn off excess carbon deposits. However, when a diesel car does lots of short journeys, the filter doesn't get hot enough for regeneration; eventually, it becomes blocked.

You can avoid this by taking your car on a longer motorway journey a few times a month. This guide discusses how much it costs to clean a DPF.

2. Broken ceramic monolith

The ceramic monolith, or filter element, of a DPF can break, triggering the warning light. This breakage is often caused by mechanical failure or by the DPF being knocked during a difficult journey.

3. Faulty temperature or pressure sensor

If either of these sensors goes, it can lead to the car's computer system registering an issue with the DPF when there isn't one.

Temperature warning light

What it looks like: My clarinet is drowning.

This light appears when your engine is overheating.

Possible causes

1. Low coolant

The first thing to check is the coolant reservoir. Without enough fluid in the system, your engine won't be able to maintain the optimum temperature and will overheat.

2. Faulty thermostat

A broken thermostat will not register the correct temperature and may incorrectly report that the engine is too hot.

3. Faulty water pump

The water pump keeps coolant moving through the system. It usually lasts between 60,000 and 90,000 miles, though it can fail earlier; when it does, your car will quickly start to overheat.

4. Blown head gasket

A blown head gasket is the worst possible explanation for why your car is overheating. Not only can it cause further engine damage, but it's also extremely expensive to replace.

This guide covers everything you need to know about head gasket failure.

Oil warning light

What it looks like: The gravy needs topping up.

This warning light is easy to diagnose.

Possible causes

1. Low engine oil

Cars tend to go through more engine oil as they get older, but even new cars need a top up from time to time. The good news is that it's easy and quick to resolve low engine oil yourself - this guide explains how.

2. Oil leak

Look in the engine bay and beneath the car to see if you can spot a leak. Even if you can't see a puddle of oil, the system may have a smaller leak.

Any leak will likely worsen with time and become more expensive to fix. This, combined with the fact that you'll have to spend more money to keep the oil at the right level, means it could be more cost-effective to book a repair immediately.

Tyre pressure warning

What it looks like: We’re out of horse shoes.

Possible causes

1. Low tyre pressure

Sensors in the tyre pressure monitoring system (TPMS) may have detected that one or more of your tyres have low pressure. This issue is easy and, best of all, free to resolve. Simply pump the affected tyre(s) up to the correct pressure.

2. Punctured tyre

One of your tyres may have sustained a puncture. If it uses run-flat technology, you can keep driving for a while; otherwise, you'll have to pull over and change the tyre (if you have a spare one) or call for help.

Battery warning light

What it looks like: Winking lego man approaching.

This light can appear due to a problem with the battery or electrical system. Find out why batteries die in this guide.

1. Weak battery

The most likely cause is a weak or discharged battery, which isn't giving your car enough power.

2. Loose cables

Check the battery cables are connected tightly.

3. Corrosion

A corroded battery may not be able to function correctly, triggering the warning light.

4. Faulty alternator

The battery warning light may not be caused by the battery at all; instead, it can come on due to an issue with the alternator.

Read about five signs of a faulty alternator here.

Glow plug warning light

What it looks like: Somebody's been testing a biro pen.

If the glow plug coil light comes on when you're trying to start your car in cold weather, it means it's cold enough for the engine to need extra heating from the glow plugs. At this point, it isn't a concern.

However, if it stays on or starts flashing, it could indicate one of the following issues.

1. Faulty glow plugs

The most obvious cause of the glow plug warning light is a problem with the glow plugs themselves. They usually last around 100,000 miles before they need replacing - this guide covers what happens when they fail.

2. A malfunctioning sensor-timer

Glow plugs are switched on and off by a timer fitted with temperature sensors. When the sensors malfunction, the timer fails, which could trigger the warning light.

3. Faulty ECU

The engine control unit (or control module) is responsible for triggering the glow plug warning light. If it stops working as it should, it may incorrectly signal an issue with the glow plugs.

Find out what else an ECU does here.

When the diesel particulate filter and EGR valve in my old diesel car became blocked, the car went into limp mode, and the glow plug light was illuminated despite there being no issue with the glow plugs, sensor or control module. This shows how tricky it can be to diagnose some warning lights correctly.

If in doubt, it's always best to seek the opinion of an expert mechanic.

Fog lights

What it looks like: A sideways jellyfish floating on the sea.

Possible causes

1. Your fog lights are on

This warning light is nothing to worry about. It alerts you that your fog lights are on. For the rear fog lights, it's yellow, and for the front ones, it's green.

Traction control

What it looks like: Your car has had too much to drink.

The traction control warning light doesn't always signal a problem. Sometimes, it simply indicates that the system has been switched off. You can find out when it should - and shouldn't - appear by consulting your vehicle handbook.

The causes below focus on the faults that can trigger the traction control light.

Possible causes

1. Malfunctioning ABS system

The anti-lock braking system is closely linked to the traction control system and can trigger the same warning light.

However, the ABS has its own dashboard symbol, too. Find out more in this guide.

2. Faulty wheel speed sensor

The wheel speed sensor provides the traction control system with information about the speed of the wheels. When it malfunctions, the system can't operate correctly. The same goes for any other sensors linked to traction control.

3. Damaged wiring

Damaged wiring is more likely to be a problem for cars that regularly endure rough road conditions.

Fuel warning light

What it looks like: A snake coming out of a bin.

Most of the time, this warning light is harmless.

Possible causes

1. Low fuel

You probably guessed it - the most common cause of this light is an almost-empty fuel tank. Once you fill up, the light should go off.

If you've ever wondered how far you can drive when the fuel light comes on, this guide is for you.

However, if you've noticed that the fuel gauge seems to go down faster than it should, it's worth investigating whether you've got a leak.

2. Faulty fuel gauge

When the fuel gauge malfunctions, it may trigger the low fuel warning light even when the tank is full. It's important to book a repair, otherwise you could end up running out of fuel mid-way through a journey.

Windscreen defrosting

What it looks like: three mushrooms growing in front of a hill.

This is another dashboard light you don't need to worry about. It has one sole purpose: to remind you that you've switched on the windscreen defrost setting.

If there's a warning light on your dashboard, you can get quotes from the best local garages using FixMyCar. All you have to do is enter your registration plate and a few details for us to generate quotes in minutes.

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• What is the ECU in a car?

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