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Car warning lights explained: what each colour and symbol means

A UK driver's guide to dashboard warning lights: what red, amber and green mean, which lights mean stop now, and what to do next.

Most dashboard lights are not emergencies, but a few really are, and the hard part is telling them apart at 60 mph. This guide explains the colour system that almost every manufacturer uses, the lights that mean you should stop as soon as it is safe, the ones that can wait for a garage visit, and the steps to take in each case. Symbols differ a little between makes, so your handbook is always the final word for your car.

The colour code: red, amber, green and blue

Car makers follow a broadly traffic-light system, set out in international standards for vehicle controls and tell-tales:

A light that flashes is usually more urgent than the same light shown steadily. A flashing engine management light, for example, often means the engine is misfiring badly enough to damage the catalytic converter.

Lights that mean stop as soon as it is safe

Oil pressure (red oil can)

This warns that oil pressure has dropped, not just that the level is a little low. Without pressure the engine's moving parts are not lubricated and serious damage can follow within minutes. Pull over safely, switch off and check the level with the dipstick once the car has stood for a few minutes. If the level is fine and the light stays on, do not drive it: call for recovery.

Coolant temperature (red thermometer)

The engine is overheating. Stop, switch off and let it cool. Never open the coolant cap on a hot engine: the system is pressurised and can spray scalding liquid. Once it is cold, check the level against the marks on the expansion tank.

Brake system (red circle with an exclamation mark)

First check the parking brake is fully released. If it is, the light can mean low brake fluid or a fault in the system. Brakes are not something to gamble on: get it checked before driving any distance.

Charging or battery (red battery)

The battery is not being charged, often because of an alternator or drive-belt fault. The car will run on stored charge for a short time, then electrics and eventually the engine will fail. Switch off non-essential electrics and head straight for a safe place or a garage.

Power steering

Steering may become very heavy, especially at low speed. Drive slowly to a safe stop and get it looked at.

Amber lights: get it checked soon

Engine management light (amber engine outline)

The car's computer has logged a fault with the engine or emissions system. It could be anything from a loose fuel cap to a failing sensor. A steady light means book it in; a flashing light means reduce speed and get it checked promptly. Since the MOT changes of 20 May 2018, an illuminated engine management light is a major defect, so the car will fail its MOT while it is on.

ABS (amber "ABS" in a circle)

Your normal brakes still work, but the anti-lock function that stops wheels locking under hard braking may not. Leave more room and get it checked.

Airbag or SRS (amber seated figure with a circle)

An airbag or seatbelt pre-tensioner may not deploy in a crash. It is also an MOT failure.

Tyre pressure monitoring (amber horseshoe with an exclamation mark)

One or more tyres has lost pressure. Check all four, including for punctures, and reset the system as your handbook describes. On cars first used from 1 January 2012, a fault with the tyre pressure monitoring system is checked at the MOT.

Traction or stability control (car with wavy lines)

Flashing briefly on a slippery road is normal: it means the system is working. If it stays on, the system may be switched off or faulty.

Diesel-specific lights

Diesels can show a glow-plug light (a coil symbol), a diesel particulate filter light and an AdBlue warning. Each needs a different fix: a particulate filter light usually means the filter needs a sustained run to clean itself (your handbook gives the exact advice), while an AdBlue warning means the tank needs topping up before the range countdown reaches zero, after which most cars will not restart.

What to do when a light comes on: step by step?

  1. Note the colour and whether it flashes. Red or flashing means act now.
  2. Check how the car feels. Loss of power, smoke, new noises, smells or heavy steering all raise the urgency.
  3. Stop somewhere safe if needed. On a motorway, use an emergency area or the hard shoulder only in a real emergency, as the Highway Code advises, and leave by the nearside doors.
  4. Look the symbol up in your handbook. Many makers publish handbooks online if you have lost yours.
  5. Do the simple checks that are safe to do: oil level, coolant level when cold, tyre pressures, fuel cap.
  6. Get a diagnosis. A garage can read the fault codes stored by the car; a basic code reader can also do this at home.

Frequently asked questions

Why do all the lights come on when I start the car?

That is a self-test. The lights should go out within a few seconds of the engine starting. One that stays on is the one to worry about.

Can I pass an MOT with a warning light on?

Not for the engine management, ABS, airbag or electronic stability control lights, and not for a tyre pressure system fault on cars first used from 2012. The MOT inspection manual lists them.

The light went out on its own. Am I fine?

Possibly. Intermittent faults are common. The fault is usually still stored in the car's memory, so mention it at the next service.

Sources and further reading

Facts checked on 20 October 2026. Spotted an error? Tell us and we will correct it.