A fuel vapour fault usually allows normal driving for now, but arrange a check and stop when safe if you smell fuel.
Trouble codes · P0440
P0440 meaning
EVAP System
The same first verdict Car Assist shows from this code alone, before a diagnosis. The code does not tell the app whether the warning light is flashing.
What this code doesn’t tell you
A code says where the car noticed a problem. It does not prove which part failed, whether the fault is still present, or what repair this car needs. The engine, other codes, freeze frame and live readings matter.
Usual causes, most likely first
The order is a starting point across cars; the exact engine and its readings can change it.
- Loose or damaged fuel cap on cars with a cap
- Leaking vapour hose
- Purge or vent valve fault
What you can check
With the engine off, check the cap is seated as the handbook describes and look for a damaged seal. Usually a fuel smell needs a stop when safe and a check before continuing.
Words the car uses
- Stored codes
- Faults the car has confirmed and saved. They help explain a check-engine light, but a code alone does not prove which part needs replacing.
- Freeze frame
- A snapshot of the engine's readings when a fault was recorded. It helps show the conditions that caused the fault, even if the car now seems fine.
- Readiness monitors
- The car's own checks of its emissions systems. An unfinished check means the car has not tested that system yet, so a clean code scan may miss a fault.
- Fuel vapour system (EVAP)
- The system that catches fuel vapour from the tank and feeds it into the engine. A leak can turn on the check-engine light, sometimes because the fuel cap is loose.
Find out what’s causing yours
Car Assist reads your car through an OBD-II adapter and your iPhone. Its assistant uses the codes, freeze frame and live readings to work through the likely cause with you.