You fill up, screw the cap back on, and drive away. Two days later, the check engine light suddenly comes on. You plug in your scanner and see P0455. Don't worry: this is almost never an expensive repair. In the vast majority of cases, it's a small leak in the fuel system, and often the culprit is simply the fuel cap.
Quick answer: Error code P0455 indicates a major leak in the EVAP system, the system that captures fuel vapor so it doesn't escape into the air. The most common cause is a loose, worn, or incorrect fuel cap. You can safely continue driving, but your car will emit fuel vapor and sometimes use slightly more fuel. Always start with the fuel cap.
What does error code P0455 mean?
Your car captures fuel vapor from the tank in a charcoal canister and sends it back to the engine at the right time. This entire system is called EVAP (Evaporative Emission Control). The car tests itself by putting the system under slight pressure or vacuum. If too much leaks out, the computer detects this as a major leak and sets P0455.
Severity: warning light. It's not an acute engine problem, you can continue driving normally. But the light will stay on, your car will unnecessarily emit vapor, and you won't pass your vehicle inspection. So fix it in good time.
Symptoms
Check engine light on. Often the only thing you'll notice. The car drives normally otherwise.
Fuel smell. Sometimes you'll notice a slight fuel vapor smell around the car, especially after refueling.
Slightly higher fuel consumption. Because captured vapor escapes instead of being reused.
Possible causes (from cheapest to most expensive)
Loose or worn fuel cap (€0 to €25). By far the number one cause. A cap that doesn't click properly or worn rubber that doesn't seal airtight.
Leak in an EVAP hose or line (€10 to €60). A crack or disconnected hose around the tank or canister.
Faulty vent or purge valve (€40 to €150). If the valve doesn't close properly, the system can't hold pressure.
Leak in the charcoal canister (€100 to €300). Less common, but possible on older vehicles.
Step-by-step guide: how to find the cause yourself
- Read and clear the code. Connect a scanner, note if there are any other EVAP codes (P0442, P0446), and clear P0455.
- Check the fuel cap. Unscrew it and screw it back on until you hear two or three clicks. Is the rubber seal still in good condition? If you're unsure, replace the cap—it costs almost nothing.
- Drive for a few days. The EVAP system only tests itself under certain conditions. If the code doesn't return after a few drives, it was the cap.
- Inspect the hoses. Look under the car near the tank and canister for cracked or loose hoses.
- Run the EVAP test. With an app like OBDeleven, you can activate the EVAP system test and see in real time whether the system holds pressure.
- Find the leak with smoke. If the leak doesn't show up, fill the system with a smoke tester. Wherever the smoke escapes, that's your leak. This is the fastest way to find a hidden EVAP leak.
What will it cost?
DIY: new fuel cap. €10 to €25. The cheapest and most common fix.
DIY: replace the hose or valve. €20 to €80 in parts.
Mechanic: diagnosis and repair. €80 to €250, depending on where the leak is.
Fix it yourself or visit a garage?
The fuel cap and visible hoses are easy to handle yourself, even without experience. If it's the purge valve or canister, or you can't locate the leak, a smoke tester or garage visit makes more sense. The good news with P0455 is you start with just a few euros and only escalate if needed.
The right tool for this code
For P0455, you need three things: read and clear the code, test the EVAP system, and actually find the leak. These three tools cover it. Start budget-friendly; grab the smoke tester only if the fuel cap wasn't the culprit.
View the Topdon CarPal →
View the OBDeleven 3 →
View the Autool SDT205S smoke tester →
Related fault codes
P0455 belongs to a family of EVAP codes. If you encounter any of these, the approach is similar: P0442 (a small leak instead of a large one), P0446 (vent valve issue) and P0457 (leak from a loose fuel cap). Not sure how to read and clear codes yet? First check out how to read and clear fault codes.
Frequently asked questions
Can I keep driving with P0455?
Yes. It's an emissions code, not an engine emergency. The warning light stays on though, and you won't pass your vehicle inspection with it.
Will P0455 go away on its own?
If you fix the cause (usually the fuel cap), the car often clears the code automatically after a few drives. Clear it with a scanner and the light goes out right away.
How many fill-ups before the code resets?
The EVAP system only tests itself under certain conditions. Expect a few days of normal driving before the car confirms the leak is gone.
Will I fail my vehicle inspection with P0455?
A lit check engine light is a fail. Clear the code before your inspection appointment.
Quick summary
• P0455 = a major leak in the EVAP system (fuel vapor recovery).
• Always start with the fuel cap; it fixes the issue most of the time.
• If that doesn't work: check hoses, run the EVAP test, find the leak with smoke.
• You can drive safely, but not pass inspection with the light on.