P0457 EVAP Leak — Fuel Cap on Smart Fortwo 451 / 453
P0457 is an EVAP leak code that specifically points to the fuel cap. On a Smart it's almost always exactly that: a loose, worn or missing cap. Fix it by reseating or replacing the cap. If the cap is good, follow the broader P0455 / P0442 procedure.
Typical Symptoms
- Check engine light with P0457
- Code appears right after fueling
- No drivability problem
- Sometimes a faint fuel smell at the filler door
What it means
The EVAP system monitors tank pressure to detect leaks. P0457 is the fuel‑cap‑specific code – the computer thinks the leak is at the filler neck. On a Smart that diagnosis is nearly always correct. If the cap is genuinely tight and undamaged, P0457 can show up alongside P0455 (gross leak) or P0442 (small leak).
Likely causes, cheapest first
- Fuel cap not fully seated. Always twist until you hear three clicks.
- Fuel cap O‑ring worn or damaged. Replace the cap with a genuine Smart/Mercedes part.
- Fuel cap missing. Left on the pump after fueling happens more often than you'd think.
- Filler neck cracked or its rubber boot torn. Inspect visually if the cap looks fine.
DIY check steps
- Inspect the fuel cap's O‑ring for cracks or flattening and replace if needed.
- Reseat the cap firmly until it clicks three times and clear the code.
- Drive two full warm‑up and cool‑down cycles. The EVAP self‑test runs once per cycle.
- If the code returns, replace the cap. If a new cap still triggers P0457, read the P0455 guide for next steps.
When to call a shop
A shop visit is rarely necessary for P0457 alone. If a fresh cap doesn't fix it and the filler neck rubber looks intact, then it's time for a smoke test – but at that point you're essentially following the P0455/P0442 process.
Related parts & typical prices
| Part | Typical price | Search |
|---|---|---|
| Fuel cap (genuine Mercedes / Smart) | $15-30 | Search Google |
| Fuel filler neck | $50-120 | 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
Stuck on this one?
SmartDiag-AI runs through the cheap-first checks with you, weighted to community-known patterns for your exact model. The link below pre-fills the code and model.