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.
"A large leak in the EVAP system — the tank's vapour plumbing is properly open to the air somewhere. And here's where the famous fuel-cap advice genuinely belongs: the number one cause of this code, by a mile, is a fuel cap left loose or sitting on the roof after a fill-up. Check that first, every time. If the cap's on tight, you're looking for something bigger than a pinhole — a hose popped off its stub, a cracked filler neck, or a purge/vent valve stuck wide open. The system only tests itself periodically, so after fixing it the light can take a few days of driving to clear on its own."
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:
A large leak in the EVAP system — the tank's vapour plumbing is properly open to the air somewhere. And here's where the famous fuel-cap advice genuinely belongs: the number one cause of this code, by a mile, is a fuel cap left loose or sitting on the roof after a fill-up. Check that first, every time. If the cap's on tight, you're looking for something bigger than a pinhole — a hose popped off its stub, a cracked filler neck, or a purge/vent valve stuck wide open. The system only tests itself periodically, so after fixing it the light can take a few days of driving to clear on its own.
Yes — this doesn't affect how the car runs or its safety at all. You're venting petrol vapour you shouldn't be, which is bad for the environment and can mean a faint fuel smell near the car, but it won't strand you. Check the cap today, fix the rest at your leisure.
Very often nothing — tightening the cap is the fix in a huge share of cases. A new cap is £10-25, a hose a few pounds, valves £20-70. Because large leaks are easy to find on a smoke test, even the diagnosis tends to be quick and cheap compared with hunting pinholes.
Not while the engine light's on — automatic fail since 2018. Mind the timing, too: fix it a good few days before the test, because the EVAP system only re-tests itself every so often, and the light needs to have gone off (and stayed off) by test day.
Free app. Plug in, and get every code in plain English, plus the connections you'd never spot.