Understanding dashboard warning lights
Cars are becoming increasingly complex and packed with technology. There are sensors to check if components are functioning properly or when features are in use. This means your car’s instruments will include countless graphics and symbols to show what’s going on (or perhaps what isn’t).
When the ignition is turned on, you should notice all warning lights come on briefly and disappear once the engine starts. This is so you can check the warning light bulbs are working. After this, if any symbols remain lit, it means either a feature is in operation - such as fog lights - or that there is an issue with something, for example you are about to run out of washer fluid.
Some cars use textual messages on LCD displays but many still rely on the simple icon to warn the driver so it is important to know what they mean. Manufacturers have mostly standardised on the symbols so here are the main ones you might see. If you are still unsure, or your car is showing something different, please refer to your vehicle’s handbook or visit a competent garage.
A car’s antilock braking system (ABS) helps when braking by preventing the wheels locking-up, thereby assisting in keeping the vehicle under control. If the warning light is on, it could mean this critical safety feature won’t operate when you need it. It is also an MOT failure.
The airbag warning light indicates an issue with an airbag, or possibly seatbelts if your car has pre-tensioning ones. It means you are at risk if involved in a collision and it is also an MOT failure. The airbag may just need resetting if you have been involved in a low speed impact where airbags were not deployed.
The battery icon indicates there is something wrong relating to the battery or the car’s charging system - perhaps the alternator or the belt which drives this. Failure of the battery or its charging could result in the loss of headlights, power steering or any other critical function so it is important to get this one checked straight away.
This is another warning you mustn’t ignore. It is a general symbol for brake-related issues. It might be that your parking brake is still on (which might just be human error), that your brake fluid is low or that your brake pads are worn down. Both low fluid or brake pads worn beyond their usable layer could compromise a car’s ability to stop safely.
One of your exterior bulbs has failed. Some cars will tell you which - in a message box - others give you the fun of walking round to find out for yourself.
This symbol is telling you that cruise control is enabled. It may not actually be operating - you will need to set or resume the speed you desire - but it’s ready to use.
This warning indicates the diesel particulate filter is becoming blocked. This is often due to too many short drives where the exhaust hasn’t reached full operating temperature. A longer drive at motorway speeds will often sort this but it is worth referring to the specific instructions in your car’s manual.
This is a catch-all for any of the engine sensors. It could simply be a sensor failure - as sensors within the engine do occasionally stop working due to the harsh conditions inside an engine - but might indicate a more serious fault. A garage’s diagnostic tool should be able to determine the issue. Typical triggers are oil pressure, the mass airflow sensor or emissions system. Some cars use an amber and red version where amber means ‘get it checked’ and red means ‘stop right now and get the vehicle recovered to a garage’.
This symbol indicates you have switched-on your rear fog lights. If you have front fog lights, the picture will show downward pointing light rays from the bulb.
The low fuel warning light should correlate with the fuel gauge and will appear when you have just a few miles range left in your tank. Different manufacturers set this at different thresholds but it is often around 50 miles.
This symbol is for the glow plugs in diesel vehicles only. They are like spark plugs but remain hot all the time to allow the compressed diesel to combust. The light may appear briefly on start-up as the glow plugs warm up but if it stays illuminated, can indicate there is a fault.
This tells you that your heated rear window is switched on. In many cars, this also heats the door mirrors. It will be on a timer and/or sensor so should switch off automatically but if your rear window and mirrors are clear, you should switch off manually.
There are many types of lane assist available on new cars. Some provide an audible warning or vibrate the steering wheel to indicate you are wandering out of your lane. Some cars provide gentle steering resistance to keep you in the lane. This symbol shows the feature is active.
Thankfully most cars now indicate your windscreen washer fluid level is low before you actually run out. Remember it is an offence to drive without washer fluid.
This symbol indicates low oil pressure in the engine. It could be down to too little oil in the engine but also might be the result of a failed or failing oil pump. Without proper lubrication, this could cause a complete engine failure - certainly expensive and likely to be dangerous if it happens when you are driving.
Automatic cars have the safety feature where the footbrake needs to be pressed while starting the car or engaging drive or reverse. This symbol indicates you need to do this.
Manual cars check that the clutch is depressed before the engine is started to prevent you accidentally starting the car in gear and lurching forward (or backward) in error.
We know the law states that everyone must wear a seatbelt; this warning symbol (usually accompanied by an irritating sound) is a reminder to the driver that someone in the car doesn’t have their belt on. The sensors are usually in each seat to detect a passenger’s weight.
Electronic stability control (ESC) is standard on almost all cars (the exceptions being models from some low-volume manufacturers). It helps control a car in the event of a skid by applying braking to individual wheels. This will help counter understeer (going straight on when you wish to turn) or oversteer (where the rear of the car starts to slide out). If it isn’t working, you won’t be assisted if you lose control of the car, for example in wet or icy conditions.
The red thermometer symbol shows the coolant in your engine is too hot. This could be due to a failed water pump, faulty fan or even insufficient coolant. You should stop and check the cause before serious engine damage occurs. Some cars also display a blue thermometer when the engine hasn’t warmed up to normal running temperature. You should drive more gently until everything is at full operating temperature.
This symbol indicates the pressure has changed in a tyre. It might be because some air has been knocked-out by hitting pothole or due to a puncture. Tyre pressure sensors - mandatory in cars since 2015 - are notorious for going wrong but it’s best to get out (somewhere safely) and check your tyres.
About the Author
Andrew is a freelance motoring journalist with a background in IT and the vehicle leasing industry. With a lifetime’s passion for all things automotive, he can be found behind the wheel of everything from vans to supercars. In addition to reviewing the latest vehicles and technology, Andrew also runs a couple of classic British motors. He lives at the edge of the Peak District with his son and cat.
Andrew Wright @theMotorWriter