What every UK dashboard warning light means, whether it's safe to drive, and what it'll cost to fix — by a mechanic with 32 years on the tools.
Red, amber and what to do about it
Red means stop safely as soon as you can: oil pressure, coolant temperature, brake system, charging fault. Continuing to drive with a red warning light is how a repairable fault becomes a new engine. Amber means the car has found a fault and wants attention soon, but is usually safe to drive gently.
The exception everyone needs to know: a flashing engine management light means an active misfire dumping unburnt fuel into the catalytic converter. Stop, switch off, and get it recovered rather than driving it another ten miles.
The lights people see most
Engine management, ABS, tyre pressure, battery and charging, DPF, glow plug on diesels, and airbag. Each one means something specific, and the guides on this site explain the cause, the urgency and the likely repair cost for each.
A light that comes on and clears itself has still stored a fault code. Reading those codes is how you find the intermittent fault before it strands you.
Why a code reader is only the start
A code is a symptom, not a diagnosis. P0171 does not mean 'fit a sensor' — it means the engine is running lean, which could be a split hose, a dirty airflow meter, a failing lambda sensor or an injector. Changing parts to chase a code is how people spend hundreds fixing nothing.
A proper diagnosis reads live data and tests the circuit before anything is replaced. That is what the workshop charge covers, and it is nearly always cheaper than the parts you would have bought guessing.
Frequently asked questions
Can I drive with an amber warning light on?
Usually yes, gently, and get it looked at soon. A flashing engine management light is the exception — stop driving.
What does a red warning light mean?
Stop safely as soon as possible. Red covers oil pressure, coolant temperature, brake and charging faults that can destroy the engine or the brakes.
Why does a light clear itself?
The fault was intermittent. The code stays stored in the module and can still be read, which is how the cause gets found.
Does a fault code tell me which part to replace?
No. A code describes a symptom. Proper diagnosis tests the circuit and live data before any part is fitted.