P0457 Code: EVAP Leak Detected (Fuel Cap Loose/Off)
The EVAP leak test found the system wide open — almost always a loose, missing or worn gas cap.
At a glance
Severity: Minor
- Meaning
- EVAP Leak Detected (Fuel Cap Loose/Off)
- System
- Emission Controls · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $15–$600
- DIY difficulty
- Very easy
Your car regularly seals its fuel vapor (EVAP) system and checks that it holds vacuum or pressure. P0457 means the test found a leak so large, typically right after a fill-up, that the ECU blames the fuel cap. Many vehicles show a 'Check Fuel Cap' or 'Check Fuel Fill Inlet' message first. The fix is usually free or cheap: tighten the cap until it clicks, or replace a worn one. The light doesn't go out immediately, because the ECU has to rerun its EVAP test over the next few drives.
Can I keep driving? Completely safe to drive. Fix the cap soon anyway: an open tank lets fuel vapor escape, and the lit light will hide any new, more serious code.
Try this first – 5-minute fix
- Re-seat the cap Remove the cap, make sure the tether or dirt isn't caught in the threads, and screw it back on until it clicks at least once. On a capless filler, insert and remove the pump nozzle a couple of times so the flap closes fully.
- Inspect the seal and the filler neck Look at the rubber O-ring on the cap: cracks, flat spots, missing pieces or grit mean it can't seal. Wipe the lip of the filler neck clean and check it for nicks or rust.
- Replace a worn or wrong cap Buy a cap listed for your exact vehicle, ideally OEM. Cheap universal caps are a common reason this code keeps coming back.
- Let the car recheck itself Drive normally for a few days. The EVAP test often needs a cold start after the car has sat for several hours and a fuel level roughly between 1/4 and 3/4 tank; once it passes on consecutive drives, the light goes out on its own.
How to read P0457
- P Powertrain
- 0 Generic (SAE)
- 4 Auxiliary emission controls
- 57 Specific fault
Symptoms
- Check engine light shortly after refueling
- 'Check Fuel Cap' or 'Check Fuel Fill Inlet' message on the dash
- Faint fuel smell around the filler door
- No change in how the car drives
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Cap not tightened until it clicked, or left at the pump
- Worn, cracked or dirty cap seal
- Wrong or low-quality aftermarket cap
- Capless filler flap dirty, damaged or not closing
- Damaged or rusted filler neck lip
- A different large leak (hose off, vent valve stuck open) misread as cap off
Diagnosis step by step
Confirm the code and look for others
Read all stored and pending codes. If P0457 appears alone, the cap is the prime suspect; if P0455, P0442 or P0446 are also present, the problem goes beyond the cap.
Tools: OBD-II scanner
Have the cap tested
Many repair shops, and some parts stores in states with gas cap testing, can pressure-test a cap on a tester in a minute. A cap that fails the test should be replaced even if it looks fine.
Tools: Flashlight
Check the filler neck and capless mechanism
Shine a light into the filler: look for a bent or rusted sealing lip, debris on a capless flap, or a flap that doesn't spring shut. A dented filler neck can defeat even a brand-new cap.
Tools: Flashlight
Smoke test if it keeps returning
If the code returns with a known-good cap, have the EVAP system smoke-tested. At that point the leak is elsewhere, usually a disconnected hose or a vent valve that stays open.
Tools: Smoke machine
Where the parts are
- 1Gas cap
- 2Charcoal canister
- 3Purge valve
- 4Vent valve
- 5Fuel pump
- 6Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| New OEM-quality gas cap | Yes | $15–$45 |
| Shop EVAP smoke test diagnosis | No | $100–$200 |
| Capless fuel filler inlet replacement | No | $150–$400 |
| Fuel filler neck replacement | No | $250–$600 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Ford
Fords with the capless Easy Fuel filler report this condition as 'Check Fuel Fill Inlet'. Dirt on the spring-loaded flap is a common cause; when filling from a gas can, use the funnel supplied with the vehicle, since other spouts can hold the flap open or damage it.
Honda
Many Hondas show a 'Check Fuel Cap' message on the dash before or alongside the EVAP code, so a loose cap is usually obvious right after refueling.
Emissions / smog test impact
Will fail
An active P0457 with the check engine light on fails an OBD-based smog or emissions test. Tightening the cap won't pass the test the same day: the EVAP monitor has to rerun first, and some states also pressure-test the gas cap itself.
Frequently asked questions
How long does the light take to go off after I tighten the cap?
Usually a few days of normal driving. The EVAP test only runs under specific conditions such as a cold start and a mid-range fuel level, and many cars need a couple of passing drives before turning the light off.
Can I clear the code myself?
Yes, with any basic OBD scanner, but the EVAP monitor then shows 'not ready' until the car completes the test. Don't clear it right before a smog check.
I bought a new cap and the code came back. Now what?
Make sure the cap is listed for your exact vehicle, then check the filler neck lip for damage. If both are fine, the leak is somewhere else and a smoke test is the next step.
Is it bad to top off the tank after the pump clicks off?
Yes. Topping off can push liquid fuel into the charcoal canister and vent lines, damaging them and causing other EVAP codes. Stop at the first automatic click.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- ISO 15031-6 – Road vehicles, diagnostic trouble code definitions (EOBD)
- US EPA – On-Board Diagnostics (OBD) program
- Manufacturer public service information (cross-checked)
- NHTSA Complaints API
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy