# P0457: Evaporative Emission System Leak Detected (fuel cap loose/off) **Verdict:** Safe to drive Emissions - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $20-$700 - **Urgency:** Keep driving - **Most likely:** Loose, missing, or worn gas cap - **DIY?:** Yes, check the cap first ## Quick answer P0457 means the engine computer has found a large leak in the EVAP system and believes the gas cap is loose or missing, usually because the leak appeared right after refueling. Many cars also show a check fuel cap message. Tightening or replacing the cap fixes most cases, though a damaged filler neck or capless filler can also set it. ## What does P0457 mean? The EVAP system keeps gasoline vapor from escaping the fuel tank. To check that it is sealed, the engine computer closes the vent valve and uses engine vacuum, a small pump, or natural pressure changes in the tank, then watches a pressure sensor to see whether the system holds. The gas cap, or the sealing flap on a capless filler, is the part of the system opened most often, so it is the most likely leak point. P0457 is a large-leak code with an extra clue. On many vehicles the computer notices that the fuel level rose, meaning you just filled up, and then the system failed to seal, so it concludes the cap was not put back properly. Some vehicles first show a fuel cap message on the dash and only set P0457 if the leak continues. Many need two failed tests before the check engine light comes on, so the light may appear a day or two after refueling. ## What are the symptoms of P0457? - Check engine light on a day or two after refueling - Check fuel cap or loose fuel cap message on the dash - Faint fuel smell near the filler door - Car drives normally - Failed emissions test while the code is stored ## What causes P0457? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Gas cap not tightened or left off** (most common). The cap is often not turned until it clicks, gets cross-threaded, or is left on the pump island. Because the computer links the leak to the refueling event, P0457 almost always points here first. Check that the cap is present, sits straight in the filler, and clicks at least once when you tighten it. 2. **Worn or damaged cap seal** (common). The rubber O-ring or gasket on the cap hardens, cracks, or flattens with age and heat, and dirt or grit on the sealing surface stops it seating. A cap that has been dropped or run over may also leak. Replacing a worn cap with an original-equipment or quality matching part is an inexpensive first fix. 3. **Dirty or damaged capless filler** (less common). Many newer vehicles have a capless filler with a spring-loaded flap instead of a cap. Dirt, ice, or a nozzle that did not fully open the flap can stop it sealing, and the flap can bend if the wrong funnel is used. Cleaning it as described in the owner's manual often fixes the code. 4. **Rusted or cracked filler neck** (less common). The metal filler neck where the cap seals can rust at the lip, especially on older vehicles in states that use road salt. A pitted sealing surface lets vapor escape even with a new cap. A shop can usually see this by removing the cap and inspecting the rim, and the neck normally needs replacing. 5. **Leak elsewhere found after refueling** (rare). Occasionally a large leak somewhere else, such as a disconnected hose or a cracked canister, happens to be detected just after a fill-up, so the computer blames the cap. If the cap and filler check out and the code keeps returning, a smoke test of the whole EVAP system finds the real leak. ## How do you diagnose P0457? 1. Remove the cap, inspect the seal for cracks or dirt, and retighten it until it clicks. 2. Inspect the filler neck lip or capless flap for rust, damage, or debris. 3. Have the cap checked on a cap tester if your inspection station or shop has one. 4. If the code returns after a week of driving, have a smoke test done on the whole EVAP system. ## How do you fix P0457, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Tighten or replace gas cap | $20-$50 | Tightening is free; a matching new cap fixes most P0457 codes. | | Clean or replace capless filler assembly | $150-$450 | For a flap that will not seal. | | Replace rusted filler neck | $250-$700 | Common on older vehicles in road-salt states. | ## Is it safe to drive with P0457? > **Safe to drive.** Yes, P0457 is safe to drive with, and if the cap was simply loose, the fix costs nothing. If the cap is missing, replace it soon, since fuel vapor escapes and dirt can reach the filler. A strong fuel smell or wet fuel near the filler should be checked promptly. ## Will P0457 fail an emissions test? P0457 fails an OBD-based emissions test in most states while the check engine light is on, and some state programs also test the gas cap separately. After tightening or replacing the cap, do not clear the code just before the test, because the EVAP monitor will then read not ready. Allow several days of driving first. ## After the repair: clearing P0457 Once the cap is tight or replaced, the light usually goes off by itself after several days of driving with no repeat of the leak, or a scan tool can clear it. The EVAP test needs certain fuel levels and temperatures, often after an overnight cool-down. A ready EVAP monitor with no pending code confirms the fix. ## How to prevent P0457 - Turn the gas cap until it clicks every time you fill up, and check it is straight. - Keep the cap tethered or in one set place so it is never left at the pump. - Wipe dirt from the cap seal and filler lip if you often drive on dusty roads. - Replace a cap with a cracked seal or broken ratchet using a matching quality part. - On capless fillers, use only the funnel supplied with the vehicle when filling from a gas can. ## Codes often seen with P0457 - [P0455](/codes/p0455): Evaporative Emission System Leak Detected (large leak) - [P0442](/codes/p0442): Evaporative Emission System Leak Detected (small leak) - [P0456](/codes/p0456): Evaporative Emission System Leak Detected (very small leak) - [P0440](/codes/p0440): Evaporative Emission System - [P0446](/codes/p0446): Evaporative Emission System Vent Control Circuit ## Frequently asked questions ### What does P0457 mean on a car? P0457 means the EVAP system has a large leak and the computer believes the gas cap is loose or missing. It usually appears soon after refueling. Tighten the cap until it clicks, and if the seal is damaged or the cap is gone, replace it with a part that matches your vehicle. ### How long does it take for P0457 to clear after tightening the gas cap? It typically clears within a few days to a week of normal driving. The computer has to rerun its leak test, which only happens under certain conditions, such as a cooled-down engine and a mid-range fuel level. A scan tool can clear it sooner, but the monitor still must rerun. ### Can I drive with a P0457 code? Yes, P0457 does not affect how the car runs and is safe to drive with. It keeps the check engine light on and will fail an emissions test until fixed. Check or replace the cap right away so the light can clear and a new problem does not go unnoticed behind it. ### What is the difference between P0457 and P0455? Both mean a large EVAP leak. P0457 adds the computer's judgment that the leak is the fuel cap, usually because it found the leak right after a refueling. P0455 does not name a location, so the leak could be a hose, a valve, the canister, or the cap. ### How much does it cost to fix P0457? Most P0457 fixes cost nothing, or $20 to $50 for a new gas cap. If a capless filler needs cleaning or replacement, expect $150 to $450 at an independent shop. A rusted filler neck usually costs $250 to $700 to replace, depending on the vehicle and how much must come apart. ### Can a new gas cap cause P0457? Yes, if it does not fit properly or is not tightened fully. Some low-quality universal caps do not seal well on every filler neck. Use an original-equipment cap or a quality replacement listed for your exact vehicle, and turn it until it clicks before you drive away. ### Why does my car say check fuel cap? The message means the computer found that the fuel system was not sealed, often after a fill-up. When it is safe, remove the cap, check the seal for dirt, and reinstall it until it clicks. The message and light should clear after several drives if the cap was the cause. ### Can a capless gas tank get P0457? Yes, capless fillers can leak if dirt, ice, or a damaged flap stops the seal from closing. Many owner's manuals explain how to clean the filler and how to use the supplied funnel for gas cans. If cleaning does not help, the filler assembly may need replacing. ### Will P0457 make me fail inspection? Yes, in most states a stored P0457 with the check engine light on fails an OBD-based emissions test. After fixing the cap, drive normally for several days so the EVAP monitor completes. Some states also test the gas cap separately, so a worn cap may fail that check too. ### Is it bad to drive without a gas cap? Driving without a cap does not usually harm the engine, but it lets fuel vapor escape, keeps the check engine light on, and lets dirt or water reach the filler neck. Get a replacement cap as soon as you can, choosing one listed for your vehicle so it seals properly. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other emissions codes - [P0440 Evaporative Emission System](https://diagxcar.com/codes/p0440) - [P0441 Evaporative Emission System Incorrect Purge Flow](https://diagxcar.com/codes/p0441) - [P0442 Evaporative Emission System Leak Detected (small leak)](https://diagxcar.com/codes/p0442) - [P0443 Evaporative Emission System Purge Control Valve "A" Circuit](https://diagxcar.com/codes/p0443) - [P0446 Evaporative Emission System Vent Control Circuit](https://diagxcar.com/codes/p0446) - [P0449 Evaporative Emission System Vent Valve/Solenoid Circuit](https://diagxcar.com/codes/p0449) - [P0451 Evaporative Emission System Pressure Sensor/Switch "A" Circuit Range/Performance](https://diagxcar.com/codes/p0451) - [P0452 Evaporative Emission System Pressure Sensor/Switch "A" Circuit Low](https://diagxcar.com/codes/p0452) - [P0455 Evaporative Emission System Leak Detected (large leak)](https://diagxcar.com/codes/p0455) - [P0456 Evaporative Emission System Leak Detected (very small leak)](https://diagxcar.com/codes/p0456) ## Symptoms - [Why does my car smell like gas?](https://diagxcar.com/symptoms/car-smells-like-gas) --- Source page: https://diagxcar.com/codes/p0457 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.