P0457: Evaporative Emission (EVAP) System Leak Detected (fuel cap loose/off) (Meaning, Causes, Fixes)
What P0457 means
The EVAP system traps fuel vapor from the tank in a charcoal canister and later purges it into the engine to be burned. During its self-test the PCM seals the system and checks whether it holds vacuum or pressure. P0457 means it found a leak, and the generic definition points to the fuel cap being loose or off. RepairPal says the gas cap is the cause most of the time. Sources describe the leak size differently: OBD-Codes.com calls P0457 a large leak in the same family as P0456 (very small) and P0455 (large), while RepairPal ties it specifically to the fuel cap rather than to leak size.
Severity: can I keep driving?
Usually OK to drive
Generally safe to keep driving: it usually causes no drivability problems. Sources differ on urgency (RepairPal rates it moderate), so fix it soon, and get it checked promptly if you smell fuel.
Common symptoms
- Check engine light on
- Usually no drivability problems
- Possibly an occasional fuel smell
- OBD-Codes.com also notes slightly worse fuel economy as vapor escapes
Likely causes
Roughly most to least common, based on the sources below. Your vehicle may differ.
- Gas cap left loose, missing, cracked, or with dirt on the threads or seal
- Cracked, rotted or disconnected EVAP hose
- Cracked charcoal canister (listed by OBD-Codes.com)
- Purge valve or vent valve not sealing (RepairPal notes these usually set additional codes too)
Diagnostic steps you can do
Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.
- Check the gas cap for dirt, cracks or a worn seal, reinstall it until it clicks, and make sure nothing is stuck in the filler neck.
- Clear the code or keep driving: OBD-Codes.com says it resets after three drive cycles without the fault, while RepairPal warns the light can take a long time to go out on its own because the EVAP system isn't checked constantly.
- If it comes back, replace the gas cap. Caps are inexpensive and RepairPal recommends replacing one if in doubt.
- Look over the EVAP hoses you can reach for cracks or loose ends.
Typical fixes
- Reseat or replace the gas cap
- Replace cracked or disconnected EVAP hoses
- Replace a cracked charcoal canister or a leaking purge or vent valve found by testing
Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.
🛠 When to call a pro
- A new cap doesn't fix it: shops use a smoke machine to find EVAP leaks, which are very hard to pinpoint without one
- Testing whether the purge and vent valves hold vacuum, and checking manufacturer technical service bulletins (TSBs)
Where to buy
Plain search links. Always match parts to your exact year, make, model and engine.
FAQs
Is P0457 covered under warranty?
OBD-Codes.com notes that emission systems are often covered for an extended period, from 80,000 to 100,000 miles depending on the vehicle. Check your own warranty booklet.
How is P0457 different from P0455 and P0456?
All three are EVAP leak codes. P0456 is a very small leak and P0455 a large leak; P0457's generic definition points to the fuel cap. The diagnosis starts the same way: cap first, then hoses, then a smoke test.
Sources
Last reviewed 2026-10-22. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.