Warning lights follow a colour code that most manufacturers share. Red means a serious problem or a safety risk: stop as soon as it is safe. Amber or yellow means something needs checking soon. Green and blue lights tell you a system is switched on. Symbols vary between makes, so the car's handbook is the final word on any light.
When you switch the ignition on, most lights come on for a moment as a self-test, then go out once the engine starts. A light that stays on, or comes on while you are driving, is the one to act on.
Red lights: stop when it is safe
| Light | What it usually means | What to do |
|---|---|---|
| Oil pressure (an oil can) | The engine is not getting enough oil pressure | Stop and switch off as soon as it is safe. Check the oil level, and do not drive on with the light lit |
| Engine temperature (a thermometer) | The engine is overheating | Stop and switch off. Let it cool before checking the coolant, and never open a hot cooling system |
| Battery or charging (a battery) | The charging system has a fault, so the car is running on its battery | Get it to a garage straight away: the car may stop when the battery runs flat |
| Brake warning (an exclamation mark in a circle, or BRAKE) | The parking brake is on, the brake fluid is low or there is a brake fault | If it stays on with the parking brake off, stop and get help |
| Airbag (a seated figure with a circle) | A fault in the airbag system | The airbags may not work in a crash. Get it checked soon |
| Seat belt, door or bonnet open | A belt is not fastened, or a door, the boot or the bonnet is open | Fasten the belt or close it before you drive |
Amber lights: get it checked soon
| Light | What it usually means | What to do |
|---|---|---|
| Engine management (an engine outline) | A fault with the engine or emissions system | Book the car in. If it flashes, it can mean a misfire that may damage the catalytic converter, so ease off and get it checked as soon as you can |
| ABS | A fault in the anti-lock braking system | The brakes still work, but without anti-lock. Get it checked |
| Tyre pressure (a tyre cross-section with an exclamation mark) | Low pressure in one or more tyres | Check and inflate the tyres. A light that flashes and then stays on can mean a fault in the system itself |
| Stability or traction control (a car with wavy lines) | Flashing: the system is working on a slippery road. Steady: switched off or a fault | Drive gently. If it stays on, get it checked |
| Power steering (a steering wheel) | A fault in the power steering | The steering may feel heavy. Get it checked |
| Diesel particulate filter | The filter is getting blocked | The handbook usually tells you to drive at a steady higher speed for a while so it can clean itself. If the light stays on, see a garage |
| Glow plug (a coil, on diesels) | The engine is warming up to start | Wait until it goes out before starting. If it flashes while you drive, there is an engine fault |
| AdBlue | The AdBlue tank is running low | Top it up. On many diesels the engine will not restart once the tank is empty |
| Brake pad wear (a circle with dashes) | The pads are near the end of their life | Book new pads soon |
Green and blue lights
These confirm that something is on: dipped headlights, full beam (usually blue), cruise control, indicators or an eco mode. They are not warnings.
Warning lights that fail an MOT
Several warning lights are checked at the MOT. DVSA's MOT inspection manual sets out when each one counts as a defect.
| Warning light | When it is a defect | Category |
|---|---|---|
| Engine management (MIL) | Not working, or showing a malfunction, on petrol cars first used from 1 July 2003 and diesels from 1 July 2008 | Major (fail) |
| ABS | Not working, or showing a system malfunction | Major (fail) |
| Electronic parking brake | Showing a malfunction | Major (fail) |
| Airbag (SRS) | Showing a system malfunction | Major (fail) |
| Stability control (ESC) | Showing a system malfunction | Major (fail) |
| Power steering (EPS) | Showing a system malfunction | Major (fail) |
| Tyre pressure (TPMS) | The system malfunctioning or obviously not working, on cars first used from 1 January 2012 | Major (fail) |
| Brake fluid | Lit, or not working | Minor (pass, recorded) |
A brake pad wear light on its own is not a fail, but the tester checks the pads, and pads worn down to the indicator are a major defect. A tyre pressure light lit because of an earlier pressure loss is not a malfunction in itself.
Warning lights when you buy a used car
- Switch the ignition on and watch every light come on, then go out once the engine runs. A light that never comes on may have been disabled to hide a fault.
- Ask about any light that stays on, and do not accept 'it is just a sensor' without a garage report.
- Check the MOT history: failures for warning lights show up there. Run the free check to see every test.
- Our test drive and inspection checklist covers the rest of the viewing.
Common questions
What does the engine warning light mean?
That the engine management system has found a fault, often in the engine or emissions system. Get it checked soon. If it flashes, it can mean a misfire that may damage the catalytic converter, so ease off and have it looked at as soon as you can.
Can I drive with the engine management light on?
If it is steady and the car drives normally, usually far enough to get it to a garage, but do not ignore it. If it flashes, or the car feels wrong, ease off and get it checked straight away. On petrol cars first used from July 2003 and diesels from July 2008, the light showing a malfunction is an MOT fail.
Which warning lights fail an MOT?
The engine management, ABS, electronic parking brake, airbag, stability control, power steering and tyre pressure lights fail the MOT when they show a malfunction, under DVSA's MOT inspection manual. A brake fluid warning light is a minor defect.
Why do all the warning lights come on when I start the car?
It is a self-test: they light up when the ignition goes on, then go out once the engine starts. If several stay on, or come on together while you drive, have the car checked.
What should I do if a red warning light comes on?
Stop as soon as it is safe, switch off and check the handbook. Red lights such as oil pressure, engine temperature and brakes mean driving on could damage the car or be unsafe.