P0457: Evaporative Emission System Leak Detected (fuel cap loose/off)
The computer thinks the gas cap is loose or missing because the EVAP system lost its seal, often right after refueling.
What P0457 means
P0457 is the code most likely to be fixed for free. It means the EVAP self test saw a large, sudden loss of seal, the kind of result the computer associates with a fuel cap that is loose or missing. Many cars run a quick check after refueling, which is why this code often appears a day or two after a fill up. The fix is usually to tighten the cap until it clicks or replace a cap with a damaged seal. Cheap, poorly fitting replacement caps can also cause it. If the cap is good and the code comes back, the filler neck sealing surface may be damaged or rusted, or there may be a larger leak elsewhere in the EVAP system, in which case a shop will smoke test it like a P0455. The code does not affect how the car drives. After the cap is fixed, the light usually turns off on its own after several drive cycles in which the EVAP test passes.
Common symptoms
- Check engine light or a check fuel cap message
- Usually appears soon after filling up
- Fuel smell near the filler
- No change in driveability
- Failed emissions test if not fixed
Most common causes
- Gas cap loose or not clicked
- Gas cap missing after a fill up
- Damaged gas cap seal
- Wrong or poor quality replacement cap
- Damaged filler neck sealing surface
What to check yourself first
Remove the gas cap, check the seal for cracks or debris, and reinstall it until it clicks. Clear the code or drive a few days; many cars turn the light off after several successful tests. If it returns, try a new cap that matches the original part.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace gas cap (shop price) | $138-$150 | Shop price for a new cap. An OE-quality cap bought at a parts store is cheaper if you install it yourself. |
| EVAP smoke test to find the leak | $61-$90 | A smoke test is the standard way to find EVAP leaks. |
| Check engine light diagnosis at a shop | $125-$183 | If the cap is fine and the code keeps returning, a shop checks the filler neck and EVAP lines. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0455 Evaporative Emission System Leak Detected (large leak)
- P0442 Evaporative Emission System Leak Detected (small leak)
- P0456 Evaporative Emission System Leak Detected (very small leak)
- P0440 Evaporative Emission System
- P0446 Evaporative Emission System Vent Control Circuit