A light comes on, and your stomach drops. Is it serious, or can it wait until the weekend? The colour-coding system is the quickest way to know — and it's simpler than most people realise.
Modern cars have hundreds of sensors, and any one of them can put a light on your dash. That's a blessing and a curse — it means problems get flagged early, but it also means a lot of guessing if you don't know what you're looking at. Let's fix that.
The traffic-light system
Almost every warning light follows a colour code (RAC):
- Red — serious, potentially dangerous. Stop as soon as it's safe and get it checked.
- Yellow / amber — something needs attention, but it's not an emergency. Get it looked at soon.
- Green / blue / white — informational. The system is just working or switched on. Nothing to worry about.
When you start the car it's normal for several lights to flash up and then go out. It's the ones that stay on that matter.
Quick rule: red means stop and check now. Amber means book it in soon. If you only remember one thing, remember that.
The lights worth knowing
Engine management light (amber or red)
The big one. Amber usually means a fault that needs checking — a sensor, the fuel system, emissions, or airflow (Auto Express). Red is more urgent. Either way, this light is also an instant MOT fail, so don't ignore it before a test.
Oil pressure (red)
If this comes on while driving, stop as soon as it's safe. Low oil pressure can wreck an engine in minutes. Don't drive on it hoping it'll clear.
Battery / charging (red)
Comes on briefly at start-up, then goes out. If it stays on, you've got a charging problem — often the alternator. See our guide on cars that won't start.
Brake warning (red)
Could be the handbrake left on, low brake fluid, or worn pads. If it stays on after releasing the handbrake, get the brakes checked.
ABS (amber)
Your normal brakes still work, but the anti-lock system has a fault. Safe to drive carefully, but book it in.
Tyre pressure / TPMS (amber)
One or more tyres is low or has a fault. Check and inflate — and look for a slow puncture if it keeps coming back.
DPF (amber, diesels)
The diesel particulate filter is clogging, usually from too many short journeys. We cover how to clear it in our DPF guide.
Why guessing costs you money
Here's the honest bit. A warning light tells you something is wrong, not what. Two cars with the same light can need completely different repairs. That's why we plug in and read the actual fault codes before touching anything — modern cars hide the real fault behind that one glowing symbol, and guessing means paying for parts you never needed. Our diagnostics start from £55, and we give clear repair recommendations, not a shopping list.
Local Service Areas: We provide expert vehicle servicing, diagnostics, and repairs for drivers across the West Midlands. Whether you need a garage in Coventry, Solihull, Kenilworth, Berkswell, Meriden, or Balsall Common, our workshop is easily accessible.
Got a warning light on? Get it diagnosed properly.
Accurate diagnostics from £55 — proper fault-code scanning and a clear explanation of what's actually wrong. Book in at our Coventry workshop.
