P0455 EVAP Gross Leak (Fuel Cap) on Smart Fortwo 451 / 453
P0455 is a large EVAP leak. On a Smart it's almost always exactly what the code suggests: a loose, missing or worn fuel cap. Seat the cap until it clicks three times, clear the code and drive two warm‑cool cycles. If it returns, replace the cap before chasing anything else.
Typical Symptoms
- Check engine light with P0455
- Code often appears right after fueling
- No noticeable drivability problem
- Sometimes a faint fuel smell if the leak is bad
What it means
The EVAP system seals the fuel tank to capture vapors. Once per key cycle the ECU pressurizes (or pulls a vacuum on) the system and watches how fast it leaks down. P0455 means it saw a leak too big to be a pinhole. On a Smart that's usually a cap that's loose, missing or has a tired O‑ring.
Likely causes, cheapest first
- Fuel cap loose. Reseat it until you hear three clicks.
- Fuel cap O‑ring worn or damaged. Replace the cap; roughly $15–30.
- Wrong cap. Aftermarket caps don't always seal a Smart filler neck; a genuine cap is a safer bet.
- Filler neck cracked or rubber boot torn. Inspect the rubber section behind the fuel door.
- EVAP hose disconnected. Rare, but check the lines from the canister to the tank.
DIY check steps
- Pop off the cap and inspect the O‑ring for cracks or compression set; screw it back on until it clicks three times.
- Clear the code with a scan tool or by disconnecting the battery for 15 minutes.
- Drive two complete cycles (cold start, warm up, shut down, cool). The EVAP self‑test runs once per cycle.
- If P0455 returns, replace the cap with a genuine Smart/Mercedes part.
- If a new cap doesn't fix it, inspect the filler neck rubber for cracks and the EVAP hoses for disconnections.
When to call a shop
If the cap is new and the filler neck and hoses all look good, a shop smoke test is next. A low‑pressure smoke generator finds large leaks quickly. Any EVAP work beyond the cap is uncommon on Smarts; if you're at this stage, make sure the diagnostic process didn't skip the basics.
Related parts & typical prices
| Part | Typical price | Search |
|---|---|---|
| Fuel cap | $15-30 | Search Google |
| Filler neck / hose | $50-120 | Search Google |
| EVAP hose / line | $10-25 | Search Google |
Prices are rough community-reported ranges, not quotes. Aftermarket vs. genuine Mercedes parts swing the spread; call a Smart-experienced shop for an actual quote.
Manual references
- Service manual on Manualslib — external mirror (we don't host this specific document).
- Browse Smart manuals on smartcarmanuals.com — pick your chassis code section on the home page if a specific manual isn't listed above.
Community references
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