GarageGuideEvaporative emissions (fuel cap)
P0457 Code: EVAP Leak Detected (Fuel Cap Loose or Off)
P0457 stands for "Evaporative Emission Control System Leak Detected (Fuel Cap Loose/Off)." The EVAP system traps gasoline vapor from the fuel tank so it does not escape into the air. The car regularly seals the system and checks that it holds pressure or vacuum.
When that test fails in a way that looks like an open fuel cap, the computer sets P0457. In most cases the fix is as simple as tightening or replacing the gas cap. Some cars also show a "Check fuel cap" message on the dash.
P0457 is not harmful to the engine and does not affect how the car drives. It does let fuel vapor escape and will fail an emissions inspection, so fix it soon.
You can keep driving normally. Tighten or replace the cap, then give the car a few days of normal driving for the light to go off.
Symptoms you might notice
- Check engine light on (steady)
- "Check fuel cap" or "Fuel cap loose" message on some cars
- The car drives normally
- Occasionally a faint gasoline smell near the fuel door
- Failed emissions inspection while the light is on
Common causes
Loose or missing gas cap
By far the most common cause. A cap that was not turned until it clicked, or was left off after filling up, lets vapor escape.
Worn or cracked gas cap seal
The rubber O-ring on the cap gets hard and cracked with age and stops sealing even when tight.
Wrong or poor-fitting replacement cap
An aftermarket cap that does not match your car may not seal properly.
Damaged or dirty fuel filler neck
Rust, dirt or a dent where the cap seals can stop it from sealing. This is more common on older cars.
Other EVAP leak
Less often, the leak is elsewhere in the EVAP system, such as a cracked hose or a faulty purge or vent valve.
Before you buy parts
Try the free fix first. Tighten the gas cap until it clicks and drive for a few days before buying anything. If the light stays off, you are done. If it comes back, replace the cap next.
What to check
- Remove the gas cap and put it back on, turning until it clicks several times.
- Look at the rubber seal on the cap for cracks, flattening or missing pieces.
- Check the filler neck opening for dirt, rust or damage where the cap seals.
- If the cap looks worn or is not the original type, replace it with one made for your car.
- After fixing, drive normally for a few days. The light often goes off on its own after several drive cycles.
Possible repairs
Tighten the cap
Free and often all it takes. The light may take a few days of driving to turn off.
Replace the gas cap
An inexpensive part and a 10-second job. Buy one that matches your car, ideally an OEM or OEM-quality cap.
Clean or repair the filler neck
If the neck is rusty or damaged, it may need cleaning or replacement by a shop.
EVAP system smoke test
If a new cap does not fix it, a shop can run a smoke test to find a leak elsewhere in the system.
Parts and tools that may help
Enter your year, make and model on the store's site to see parts that fit your car.
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Frequently asked questions
What does P0457 mean?
It means the EVAP system detected a leak that looks like a loose or missing fuel cap. Tightening or replacing the gas cap fixes it most of the time.
How long does it take for the light to go off after tightening the cap?
Usually a few days of normal driving. The car has to run its EVAP self-test again, which needs certain conditions, so it may take several drive cycles.
Can I drive with code P0457?
Yes. It does not affect how the car runs. Fix it soon because it lets fuel vapor escape and will fail an emissions test.
What is the difference between P0457 and P0455?
Both are EVAP leaks. P0457 specifically points to the fuel cap. P0455 means a large leak somewhere in the system, which is often still the cap but can be a hose or valve.