P0457: EVAP System Leak (Fuel Cap Loose or Off)
P0457 means the car's fuel vapor (EVAP) system found a large leak, and the most likely reason is a fuel cap that is loose, not clicked shut, or missing. It is usually not urgent and often fixed by tightening the cap, but the warning light will stay on until the system rechecks itself.
You can keep driving
The code does not cause limp mode, and the main effect is a vapor leak and a lit warning lamp. Check the cap soon, because a fuel smell or an emissions problem can follow if the leak continues.
What it means
The EVAP system traps fuel vapor from the tank in a charcoal canister instead of letting it escape into the air. A purge valve lets the engine pull that vapor in and burn it, and a vent valve opens the canister to fresh air when needed. After refueling, the computer expects the system to build a slight vacuum (suction). If it does not, as with Ford, which looks for about -2 kPa within 30 seconds, the computer assumes the fuel cap was left open or is not sealing and sets P0457. Some makes may turn on a separate check fuel cap lamp instead of the regular warning light. The code clears once the cap is found tight again. Ford sets the lamp after two to three trips depending on calibration, and Subaru after two. GM and Saab's ME9 system do not use this code.
Likely causes
- Fuel cap not closed, not clicked in or forgottenVery likely
The code is defined around the cap, and a cap left loose or off after refueling is the most common reason for a large leak.
- Fuel cap seal faulty or non-original capPossible
A worn seal or a cap that does not fit correctly cannot hold the vacuum the system needs.
- Filler neck sealing surface damaged or capless flap stickingPossible
If the surface the cap seals against is damaged, or the flap in a capless filler does not close, air gets in even with the cap on.
- Vent valve stuck openLess likely
A vent valve that stays open lets air into the system so it cannot hold vacuum.
What you may notice
- Check fuel cap lamp or check engine light on
- Fuel smell
- EVAP readiness not set (the car's self-test for this system has not completed)
What to check, cheapest first
- 1Check that the fuel cap is on and turn it until it clicks. Make sure it is not cross-threaded. · you can do it
- 2Inspect the cap's rubber seal for cracks, flattening or dirt, and confirm the cap is the correct type for the car. · you can do it
- 3Look at the filler neck sealing surface, and on a capless filler check that the flap moves freely and closes. · you can do it
- 4Replace the cap if the seal is damaged or the cap is not original, then clear the code and drive normally. A drive cycle (a set pattern of driving) is needed for the system to retest itself. · you can do it
- 5If the code returns, read the related codes (P0455, P0442, P0456, P0446, P0464) to see whether other EVAP faults are present. · mechanic
- 6Test the vent valve and check for leaks in the system if the cap and filler neck are fine. · mechanic
Related codes
Frequently asked questions
Can I drive with a P0457 code?+
Yes. The code does not put the car into limp mode. Check the cap soon so the leak and warning light are resolved.
Can a loose gas cap cause P0457?+
Yes. That is the most common cause. A cap that is loose, not clicked shut or left off after refueling is what this code is designed to detect.
Will P0457 pass an emissions test?+
Probably not while the code is active. The code is emissions-related and the system's readiness may not be set until it has retested after the repair and a drive cycle.
How long does it take for the light to go off after fixing the cap?+
The code clears once the cap is found tight again, but the system must recheck itself over a drive cycle. Some makes need two or three trips to set the lamp, so clearing may take a few trips as well.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10