Car dashboard warning lights: the complete guide
Your dashboard lights up with lots of symbols each time you start the car, but what do they mean – and what if one stays on?
All cars have a variety of dashboard warning lights, such as the engine management light or oil pressure warning light, that relate to different systems. On many cars, these lights will appear for a few moments when you switch on the ignition but should soon go out again. If one or more of these warning lights stays on when the engine is running, there could be a problem with your car.
Dashboard warning lights are displayed by colour in red, amber, green and blue on a spectrum of how serious the problem is. While blue and green warning lights are less urgent, we advise you to take the same precautions as you would for the more serious warnings to prevent damage to your car: it’s best to quickly stop where safe to do so and consult your car’s handbook for further advice before continuing with your journey.
Some problems will be easy to fix and not particularly urgent; a low windscreen washer fluid warning, for example. Other more serious faults denoted by red and amber warning lights will need to be promptly checked by a professional, especially if they relate to the brakes, engine, oil or gearbox.
The majority of warning lights are common to all makes and models of cars, although their precise locations, on or around the dashboard, may vary. Study your car’s handbook to familiarise yourself with what they all mean. Meanwhile, below, we guide you through the most important of them.
Check engine light
If this warning illuminates, it's very important to get your car checked, even if it feels completely normal to drive. This is because it warns of a potential problem with the engine, which you’ll want to avoid damaging at all costs. This light can come on for a very wide range of problems, so while it’s likely to be just a faulty sensor or minor issue, a proper diagnosis is critical to prevent potential damage.
Oil pressure warning light
Aside from a brake warning light, an oil warning light is one of the most serious warning lights of all, hence it being red. Oil pressure is generated by the oil pump keeping the engine oil circulating and by the quantity of oil in the engine. A leak, a faulty pump or too little (or even too much) oil can cause damage to the engine, very likely resulting in huge repair bills or even a write-off. So while you should never ignore any warning light, this one is especially important to heed; stop the engine immediately and consult the handbook. You may simply have to top up the oil to make the light go out - if it remains on, there could be a much more serious issue that requires a garage to investigate.
Brake system warning light
Another red warning, this brake system warning light also requires urgent attention. It may be that you've left the handbrake engaged slightly while pulling away, so ensure it's fully released - some cars may instead have the letter ‘P’ instead of an exclamation mark to represent that the parking brake is on. If this doesn’t solve the problem, or the warning light appears as you're driving along, pull over safely and call for roadside assistance or arrange for the car to be taken to a garage. It may be that the brake fluid level is too low and simply needs topping up, or that a brake pad wear sensor is faulty. However, it could also be a more serious issue with the braking system. While you can’t take the risk either way, if the pedal feels spongy when you press it, or sinks all the way to the floor, then it’s easy to tell that a significant issue has occurred and the car should definitely not be driven any further.
Battery charge warning light
This warning light can indicate a number of things, all relating to the car’s battery and charging system. This is a particular problem at night, because a faulty battery can lead to headlights failing, but without the battery or charging system providing electricity, you may find power steering, brake servos or the engine itself stop working.
The cause of the warning light may be as simple as a faulty battery that’ll need replacing. But it could also be due to a problem with the car’s wiring or, more seriously, a fault with its alternator or drive belt. Other signs of a failing battery could be dim headlights or an engine that’s reluctant to start. Most garages can check your car’s battery and charging system to identify what’s at fault. Find out how to change your car's battery.
Temperature warning light
This one is pretty self-explanatory. If you see the light on at any time after start-up, then the engine is running too hot or there isn’t enough coolant (also called antifreeze) in the system. This may be due to a number of issues, all of which could leave you stranded in a cloud of steam. It could be that the car’s radiator is leaky, clogged or broken – you’ll likely see coolant dripping out if this is the case. It could also be due to a faulty water pump. More serious is a blown head gasket, which can signal catastrophic failure if you don’t turn off the engine immediately. White smoke from the exhaust could be a sign of head gasket failure. Some cars may also have another one of these lights but blue. This light means that your engine is cold, so it should appear when you are starting your car after it has been sat for a while. The blue light isn’t one to worry about but it’s advisable not to push your engine too hard until it has disappeared.
In any event, if you notice this red light, stop the car immediately, as running hot for too long can lead to total engine failure. If your car is constantly overheating, you need to get it looked at by a garage.
Low-fuel warning light
This is fairly self-explanatory, but we’ll go through it anyway. This is a warning light that comes on when the amount of fuel in the tank has passed a certain level. It’ll usually come on when you’ve got around 50-70 miles of range, and is designed to give enough warning so you can find a fuel station. Running out of petrol won’t cause any mechanical damage, but stopping on the road due to running dry is an offence. If you run out of diesel, it’ll be necessary to bleed the air from the fuel lines and injectors before the engine will start properly. That means it’s more than simply topping up from a jerrycan.
If you’re using more fuel that you’d expect, it could mean that you have a fuel leak (check the ground under your car; especially your driveway or parking space), or your car’s on-board computer (ECU) is telling the engine to use more fuel than it needs. A garage will be able to check this for you.
Tyre-pressure sensor warning
Tyre-pressure monitoring systems (TPMS) are an increasingly common sight; indeed for the last few years, it’s been mandatory for carmakers to fit the system. Essentially, it constantly monitors the amount of air in the tyres. If it detects a drop, it’ll provide a warning. This is important, because low tyre pressures can adversely affect braking and cornering and a sudden drop in pressure can cause a dangerous blow-out at high speed. If the TPMS system alerts you to low pressure, you’ll need to check and inflate the tyre. If it has an obvious puncture, you’ll need to change the wheel or use a puncture repair kit.
Traction-control warning light
You’ll most commonly see your car’s traction-control warning light when the wheels lose grip, usually in the rain or snow. It gives a visual indication that you’re close to the limit of grip. If it’s on constantly, it usually means it’s deactivated – either by a fault or by you switching the system off. If it’s the former, you’ll need to get the system checked, if it’s the latter, you should switch the system back on.
Glow plug warning light (diesels only)
Unlike petrol cars, diesel-powered vehicles don’t need a spark to make the air/fuel mixture go ‘bang’ and get the whole engine running. Instead, they use compression and temperature to induce combustion in the mixture. Every diesel has ‘glow plugs’ that are used to turn up the heat and the above symbol indicates that something’s wrong with the plugs themselves or the systems and computers that control them. You may not notice anything wrong at first, but issues with glow plugs can induce early and/or late combustion (known as ‘knocking’) that’ll make your engine sound a bit rough and not run as smoothly or efficiently as it should that could also result in a drop in fuel economy.
Seatbelt warning light
These days, the vast majority of new cars come with a system to let you know if any of your passengers haven’t got their seatbelts fastened. There’ll usually be a light – as above – to tell you if this is the case. Cars use pressure sensors in the seats and sensors in the seatbelts – so if there’s a certain amount of weight on a seat and the seatbelt isn’t secured, it’ll let you know. These warnings may be accompanied by a noise, too.
Door/boot/bonnet warning lights
Like the seatbelt light, these lights don’t usually mean that there’s anything physically wrong with the car (unless the sensor that sends the signal to the light is itself faulty). Instead, they tell you that one of the openings – be it a door, boot or bonnet – is open. This is often obvious if, for example, you’re putting the weekly shop into the boot or securing your children in the back seats. But these lights also tell you if a door, boot or bonnet hasn’t been shut properly and is only loosely closed, so they can be very useful.
Hybrid and electric vehicle warning lights
As electrified cars become ever more popular, they bring with them a new selection of warning lights to decipher.
The following warning lights appear exclusively on hybrid and electric vehicles.
Ready to drive warning light
Unlike a standard petrol or diesel, a hybrid or electric vehicle will be virtually silent when starting up. To avoid any confusion, this light simply informs you that your car is ready to be driven, so there is no cause for concern.
Limited power warning light
Having a tortoise on the dashboard may seem fun but this warning light actually means that your vehicle is running on limited power. There are a number of faults that could be causing this lack of power and they vary in severity. It’s best to stop the car as soon as is safely possible and arrange for it to be taken to the garage for a diagnosis.
Battery charge level warning light
This light will appear if your battery is at a critically low level of charge. If you do not stop the vehicle soon, you could end up stranded. The best, and most obvious, course of action is to seek the nearest available charging point, whether this is at home or a public facility.
Pedestrian alert system
Because electric and hybrid vehicles can be so quiet, especially at low speeds, it can be difficult for pedestrians to hear them approaching. In order to prevent any accidents, these vehicles are usually fitted with a system that emits a sound to alert pedestrians to your presence, without the aggression of using the horn. If this light stays illuminated, regardless of your speed, then there is a fault with this system. This will require a dealer visit in order to determine the problem.
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