A light comes on while you're driving and you're not sure whether to pull over or carry on. Warning lights are the car's way of telling you something has changed. Some mean stop now. Others mean get it looked at soon. This guide explains the difference in plain words.

Every car is a bit different, so your handbook is the final word on what each symbol means. If you've lost it, most manufacturers put handbooks online.

The colour tells you most

Most cars use a simple colour code:

  • Red usually means a serious problem or a safety issue. Stop as soon as it is safe and find out what's wrong.
  • Amber or yellow usually means something needs checking soon. You can often carry on carefully, but don't ignore it.
  • Green or blue usually just tells you something is switched on, like headlights or cruise control.

The Highway Code (opens in a new tab) says to make sure you understand all the warning displays on your car and not to ignore them, because they could mean a dangerous fault is developing. When you start the car, warning lights come on briefly and should go out once the engine is running. If one stays on, or comes on while you're driving, stop and look into it.

Red lights: stop when it is safe

If one of these comes on, find a safe place to stop. On a motorway, that means leaving at the next exit or using the hard shoulder or an emergency area. Read car broken down in Glasgow: what to do for the safety steps.

  • Oil pressure (an oil can). The engine may not be getting enough oil. Driving on can wreck it quickly. Stop, switch off, and check the oil level once the engine has cooled a little.
  • Engine temperature (a thermometer in liquid). The engine is overheating. Stop and switch off. Never open the coolant cap while the engine is hot.
  • Brake warning (often a circle with an exclamation mark, or the word BRAKE). Check the handbrake is fully off. If it is, the brake fluid may be low or there may be a brake fault. Don't carry on driving until it's checked.
  • Battery or charging (a battery symbol). The battery may not be charging. The car will run on what's left in the battery and then stop, often with the lights and wipers failing first. The Highway Code says to have this checked as soon as possible.
  • Power steering (a steering wheel, often with an exclamation mark). Steering may become very heavy.

Amber lights: get it checked soon

  • Engine management (an engine outline). Something in the engine or emissions system has been flagged. If it's steady and the car drives normally, get it checked soon. If it's flashing, or the car is shaking or losing power, stop, as continued driving can cause more damage.
  • ABS (the letters ABS in a circle). Normal braking should still work, but the anti-lock system may not. Drive gently and get it looked at.
  • Airbag (a person with a circle in front). The airbags may not work in a crash. Get it checked soon.
  • Tyre pressure (a horseshoe shape with an exclamation mark). One or more tyres may be low. Check the pressures. If a tyre is going down fast, stop.
  • Diesel particulate filter (a box with dots inside, on diesel cars). The filter needs to clear itself, which usually needs a longer run at steady speed. Your handbook will explain. If it doesn't go out, see a garage.
  • Glow plug (a coil, on diesel cars). Normal for a few seconds on a cold start. If it flashes or stays on while driving, get it checked.

Warning lights and the MOT

Some warning lights left on can mean an MOT fail. Lights for the engine management, ABS, airbags and some others are checked during the test. If a light has been on for a while, deal with it before the MOT is due. You can see what a car failed on before with the free MOT history check.

If your car has already failed, our MOT failed in Glasgow page explains your options.

Getting it checked without overpaying

Many garages and some parts shops can read the fault codes stored by the car. A code points to the area of the problem, not always the exact part, so treat a code alone as a starting point rather than a diagnosis. Ask what the check costs before they start, and ask for the codes in writing.

Our garage directory lists repair garages around Glasgow from DVSA and OpenStreetMap data. They're not our partners and we don't rate them, so check reviews and prices yourself.

Where we can help

Not sure what the light means or whether the repair is worth it? Tell us what's showing, and send a photo of the dashboard if you can. A real person reads it and will help you work out what to do next. It's free to ask and there's no obligation. If the fix costs more than the car is worth to you, you can also tell us about the car; we buy some cars as they are. If the car is in a dangerous place or anyone is hurt, call 999 first.