Officially? A wall of jargon. To most people? Absolutely nothing. That's exactly why we built the app.
Plug into any code reader and you'll get the same line every other app shows you. Technically correct. Practically useless.
"Your EVAP system — the sealed plumbing that stops petrol vapour from the tank escaping into the air — has a small leak. Small means small: the system's found a pinhole-sized escape, not fuel dripping anywhere. The honest first check is the fuel filler cap: a worn or cracked cap seal is a classic cause of the *small*-leak code (a cap left loose or off tends to throw the large-leak code, P0455, instead). After the cap it's perished rubber hoses, a weeping purge or vent valve, or corrosion on the filler neck. Petrol cars only — diesels don't have this system."
Worth checking in roughly this order. Don't jump straight to the expensive fix:
The code itself is a snapshot. The fault sets after the car's watched the numbers over a whole drive cycle. Here's what's worth keeping an eye on:
Illustrative panels. These readings aren’t in our free demo drive, but the app shows them live from your own car.
Codes rarely tell the whole story. The clever part is reading them together, and against your exact car. Here's the kind of thing it catches:
Your EVAP system — the sealed plumbing that stops petrol vapour from the tank escaping into the air — has a small leak. Small means small: the system's found a pinhole-sized escape, not fuel dripping anywhere. The honest first check is the fuel filler cap: a worn or cracked cap seal is a classic cause of the *small*-leak code (a cap left loose or off tends to throw the large-leak code, P0455, instead). After the cap it's perished rubber hoses, a weeping purge or vent valve, or corrosion on the filler neck. Petrol cars only — diesels don't have this system.
Completely fine. Nothing about how the car drives changes — you're leaking tiny amounts of petrol vapour, not fuel. There's no safety issue and no risk of breakdown. It's one of the most relaxed codes there is; fix it at your convenience.
If a new fuel cap does it, £10-25 and you're done. Hoses and valves are usually £15-60 in parts. The real cost is finding the leak — a garage smoke test (often £30-60) pinpoints it and saves you replacing parts on spec. The canister is the dear end but rarely the culprit.
Not with the engine light on — automatic fail since 2018, even for a fault this benign. The system itself isn't separately tested. Swap the cap or fix the hose, make sure the light stays off through a few drives (EVAP tests run on their own schedule), then book the test.
Free app. Plug in, and get every code in plain English, plus the connections you'd never spot.