OBD CodesWhat it means
Petrol gives off vapour. The EVAP system traps it in a charcoal canister and later feeds it to the engine to be burnt, so it does not escape into the air. The computer tests the system for leaks. The most common cause of a leak code is simply a fuel cap that is loose or has a worn seal.
Codes in this group
| Code | Meaning |
|---|---|
| P0440 | Fuel vapour system fault |
| P0441 | Fuel vapour purge flow incorrect |
| P0442 | Small leak in the fuel vapour system |
| P0443 | Purge valve circuit fault |
| P0444 | Purge valve circuit open |
| P0445 | Purge valve circuit shorted |
| P0446 | Vent control circuit fault |
| P0447 | Vent control circuit open |
| P0448 | Vent control circuit shorted |
| P0449 | Vent valve circuit fault |
| P0450 | Fuel vapour pressure sensor fault |
| P0451 | Fuel vapour pressure reading out of range |
| P0452 | Fuel vapour pressure sensor signal low |
| P0453 | Fuel vapour pressure sensor signal high |
| P0454 | Fuel vapour pressure sensor signal cuts in and out |
| P0455 | Large leak in the fuel vapour system |
| P0456 | Very small leak in the fuel vapour system |
| P0457 | Leak in the fuel vapour system, fuel cap loose or missing |
Bank 1 is the side of the engine that has cylinder 1. Sensor 1 is before the catalytic converter and sensor 2 is after it. More terms explained.
What you may notice
- Usually only the warning light
- Smell of petrol near the car
- Hard starting just after refuelling (purge valve stuck open)
Common causes
Most likely first:
- A loose, damaged or wrong fuel cap
- A cracked hose or filler neck
- A purge valve stuck open or closed
- A faulty vent valve, often blocked with dust
- A leaking charcoal canister
What to check first
- Remove the fuel cap and refit it until it clicks
- Check the rubber seal on the cap for cracks
- The light may take several days of driving to go out after the cap is fixed
- Do not keep filling after the pump clicks off: overfilling floods the canister
Have a mechanic confirm. A fault code tells you which system reported a problem, not which part has failed. The same code can have several causes, and they differ between car models. Use this page to understand the code, then have a qualified mechanic test the car before any part is replaced.
After the repair
Once the cause is fixed, the code can be cleared with a scan tool, or the warning light goes out by itself after several trips without the fault. Clearing a code without fixing the cause only hides it for a while. More about clearing codes.
Related codes
Exhaust gas recirculation (EGR) (P0400), Secondary air injection (P0410), Catalytic converter efficiency (P0420), Diesel particulate filter (DPF) (P2002), Diesel exhaust fluid (AdBlue) and SCR system (P203F). All codes.
Written in November 2026. These are generic OBD-II codes, the same on all makes. Causes and repair steps differ between models.