Warning Lights and Which Ones Mean Stop

The colour convention

Red indicates a fault requiring you to stop as soon as it is safe. Continuing risks serious damage or a safety failure.

Amber or yellow indicates a fault requiring attention soon but not immediate stopping.

Green and blue are informational, confirming a system is active.

Red lights that mean stop now

Oil pressure, usually an oil can symbol. Low oil pressure destroys an engine within minutes. Stop, switch off, check the level, and do not restart if the light persists.

Coolant temperature or a red thermometer symbol. Overheating warps cylinder heads and fails gaskets. Stop and allow it to cool; do not open a hot system.

Charging system, a battery symbol. The vehicle is running on battery alone and will stop when it depletes. Drive to a safe place immediately.

Brake system warning, which may indicate low fluid or a hydraulic fault. Treat as urgent.

Amber lights to investigate promptly

Engine management, which covers a wide range from a loose fuel cap to a failing sensor. Flashing rather than steady usually indicates a misfire that can damage the catalytic converter, and that warrants stopping.

Tyre pressure monitoring, which may indicate a slow puncture. Check pressures before continuing far.

Anti-lock braking, meaning the system is disabled while normal braking remains. Avoid heavy braking and get it checked.

Diesel particulate filter, indicating the filter needs regeneration. Following the manufacturer's guidance promptly avoids a costly replacement.

What to do generally

Keep the handbook accessible, since symbols vary between manufacturers.

Note whether the light is steady or flashing, and what the vehicle was doing, since this helps a garage diagnose.

Diagnostic code readers are inexpensive and identify the fault code, which turns a vague warning into specific information.

Do not clear codes without understanding them, since that removes the evidence rather than the fault.

What to carry and check regularly

Checking oil and coolant levels monthly catches the conditions that trigger the most serious warnings before they occur.

Both should be checked with the engine cold and the vehicle level, following the handbook.

Keep a litre of the correct oil and a bottle of the correct coolant in the vehicle, since topping up promptly is what prevents damage.

Lights that come on and go off

An intermittent warning indicates an intermittent fault, which is still a fault and is harder to diagnose once the light has cleared.

Note the circumstances: cold start, hard acceleration, after rain, at a particular speed. That context is frequently what identifies the cause.