Last checked against official sources on 2 October 2026.
This guide is general information, not legal, tax, financial or mechanical advice. Rules, rates and fees change, so confirm the details with the official sources listed at the end before you act. CarQnA is not affiliated with any of them.
A warning light is your car telling you something has changed. Some mean pull over now; others mean book it in this week. The colour tells you how urgent it is, and knowing the difference can save you an engine, or at least a wasted trip to the garage. Your handbook always has the exact meaning of every symbol on your model.
The colour code
- Red: a serious problem or safety risk. Stop as soon as it is safe and do not keep driving.
- Amber or yellow: something needs attention soon. You can usually drive carefully, but get it checked.
- Green or blue: information only, such as dipped headlights, cruise control or main beam.
Red lights: stop safely
Oil pressure (an oil can)
Low oil pressure can wreck an engine in minutes. Pull over, switch off, and check the oil level once the engine has settled. If the level is fine and the light stays on, do not drive it: have it recovered.
Engine temperature (a thermometer)
The engine is overheating. Stop and switch off. Never open the coolant cap on a hot engine, as the contents are under pressure. Low coolant, a leak or a failed fan or water pump are the usual causes.
Brake system (an exclamation mark in a circle)
First check the handbrake is fully off. If it is, the light can mean low brake fluid or a fault in the braking system, so get it checked before driving any distance.
Charging system (a battery)
The battery is no longer being charged, usually because of the alternator or its drive belt. The car will run on the battery alone for a while and then stop, so head straight to a garage or somewhere safe.
Amber lights: get them checked
Engine management (an engine outline)
The engine's computer has logged a fault, which could be anything from a loose fuel cap to a failing sensor. If it is steady and the car drives normally, book a diagnostic check soon. If it is flashing, the engine is usually misfiring, which can damage the catalytic converter: slow down, avoid hard acceleration and get it looked at as soon as possible.
ABS
The anti-lock braking system has a fault. Your normal brakes still work, but the wheels could lock in a hard stop. Get it checked soon.
Tyre pressure (a tyre cross-section with an exclamation mark)
One or more tyres is low. Check all four pressures, including a slow puncture, and reset the system once they are right.
Airbag or seatbelt system
A fault in the airbag system means the airbags may not deploy in a crash. It needs to be checked promptly.
Diesel particulate filter and glow plugs
On diesels, a DPF light means the filter is clogging, often from lots of short trips; a longer run at steady motorway speed can let it clear, but if it stays on it needs a garage. A coil symbol that stays on or flashes points to a glow plug or engine fault.
Electric and hybrid cars
Electric and hybrid cars have their own symbols, including warnings for the high-voltage system and a reduced-power mode, often shown as a tortoise. A red high-voltage or system warning is a stop-safely light: do not try to investigate the high-voltage parts yourself. Your handbook lists the symbols for your model.
Warning lights and the NCT
The NCT checks brakes, steering and suspension, lights and much more. A warning light usually means a fault in one of those systems, and that fault can fail the test. Get any warning light diagnosed and the fault repaired before your NCT, rather than having the light cleared: the fault will simply come back.
Reading the fault code
Modern cars store fault codes that any garage can read with a diagnostic tool, and inexpensive OBD code readers let you read them yourself. The code tells you which system is complaining. It is where a repair starts, not the repair itself.
Common questions
Can I drive with the engine management light on?
If it is steady and the car drives normally, you can usually drive carefully to a garage. If it is flashing, the engine is probably misfiring: slow down and get it checked as soon as possible.
What does a red warning light mean?
A serious problem, such as low oil pressure, overheating or a brake fault. Stop as soon as it is safe.
Will a warning light fail the NCT?
The light points to a fault, and a fault in a tested system such as the brakes can fail the NCT. Get it diagnosed and fixed before your test.
Why is my tyre pressure light on?
At least one tyre is below the pressure the system expects, often from a slow puncture or cold weather. Check and adjust all four, then reset the system.