P0456 Very Small EVAP Leak
Drive normally - check soon
The fuel vapor system has a very small leak, about the size of a pinhole. Check the gas cap first. The car drives the same, but it will fail an emissions test until you fix it.
- Safe to drive?
- Yes
- Typical cost at a shop
- $61-$643 RepairPal national averages, parts and labor
- Emissions test
- Yes, while the check engine light is on, most OBD emissions tests fail the car.
- Carmaker bulletins
- 2 notes with links
Check if the gas cap fixed it: clear the code and watch the EVAP readiness monitor.
$34.99 preorder, regular price $49. Free shipping in the US.
Codes and live sensors are free in the app. Obie, the AI mechanic, is part of ScanMyCar Pro.
What it means
Your fuel system is sealed so fuel vapor is stored and burned instead of escaping. The computer tests the seal now and then by holding a small pressure or vacuum on the tank. P0456 means it found the smallest leak the test can detect. It has no effect on how the engine runs.
The technical version
The EVAP monitor closes the vent valve, uses the purge valve or a pump to pull or push a small vacuum or pressure, and watches the tank pressure sensor. A slow decay means a leak: P0456 for a very small one, P0442 for a small one, P0455 for a large one. Because the leak is so small, temperature and fuel sloshing can affect the test, and many very small leaks are hard to find without a smoke machine.
Official name: Evaporative Emission System Leak Detected (Very Small Leak).
Symptoms
- Usually only the check engine light.
- Sometimes a faint fuel smell near the car.
Causes, most likely first
| Cause | How likely | How to tell |
|---|---|---|
| A gas cap that is loose or has a hard or cracked seal | most common | The cap does not click, or the rubber seal looks flat or cracked. |
| A tiny crack in an EVAP hose or at the filler neck | common | A smoke test shows it. |
| A vent or purge valve that does not seal fully | less common | Other EVAP codes may come with it. |
| A fault in the leak-detection sensor or pump | rare | Check the make notes below. |
How likely is our ranking from repair data and common practice, not a published rate.
What the live data shows
There is no single live reading that proves this fault. The useful ones are fuel tank pressure (where fitted) and EVAP purge percentage. The real check is the EVAP readiness monitor: after a fix, it should show complete within a few days of normal driving, and the code should not return.
What to check first, in order
-
Check the gas cap: present, tight, clicks, seal not torn.
It is the classic cause.
What the data shows: No reading needed.
Cost: $138-$150 at a shop (Gas cap replacement, RepairPal)
-
Clear the code and drive a few days.
The EVAP test needs time to run.
What the data shows: EVAP readiness changes to complete.
Cost: no cost if you have a scanner
-
If it returns, have a smoke test done.
It finds a pinhole that you cannot see.
What the data shows: Not a scanner step.
Cost: $61-$90 at a shop (Emission system diagnosis (shop), RepairPal)
-
Replace the part the smoke test finds.
Often a hose, a valve or the canister.
What the data shows: EVAP readiness completes and the code stays away.
Cost: $558-$643 at a shop (EVAP canister replacement, RepairPal)
Is it safe to drive?
Drive normally - check soon
Yes. It is a fuel vapor fault, not a fuel leak.
Harmless to drive with. You lose a little fuel vapor and keep the check engine light on, which can hide a new fault. You will fail an emissions test until it is fixed.
Stop driving and get help if
- You see liquid fuel dripping or smell strong fuel inside the car.
What it costs
| Repair | Typical cost |
|---|---|
| Emission system diagnosis (shop)RepairPal, updated September 3, 2026 | $61-$90 |
| Gas cap replacementRepairPal, updated September 3, 2026 | $138-$150 |
| EVAP purge valve replacementRepairPal, updated September 3, 2026 | $210-$251 |
| EVAP canister replacementRepairPal, updated September 3, 2026 | $558-$643 |
National averages for the full job at a shop, parts and labor, from RepairPal (updated September 3, 2026). Your price depends on the car and the area. Many of the first checks on this page cost nothing with a scanner. The EVAP purge valve was CarMD's number 6 check engine repair in 2025, at an average of $172. CarMD averages come from a different method (repairs reported by its users), so they can sit below RepairPal's shop estimates.
Sources for the notes: CarMD 2026 Vehicle Health Index (press release, April 22, 2026).
Can I clear it? Will it come back?
The EVAP test only runs under certain conditions, often a cold start after the car has sat for hours, with the tank between about a quarter and three quarters full. After the repair, clear the code and drive normally for several days. The EVAP monitor should show complete and the code should stay away.
Will it fail an emissions test?
Yes, while the check engine light is on, most OBD emissions tests fail the car.
Carmaker notes
Service bulletins and warranty extensions that name this code. Ask a dealer to check your VIN.
-
Infiniti 2012 and newer
Infiniti bulletin EC13-015h (November 2020) says a loose fuel filler cap may be the cause of P0442, P0455 or P0456. Check the cap first.
Infiniti EC13-015h via NHTSA static.nhtsa.gov
-
Hyundai certain 2011-2015 Sonata Hybrid
Hyundai bulletin 21-FL-002H (June 2021): salt deposits in the leak-detection sensor can set P0442, P0455 or P0456.
Hyundai TSB 21-FL-002H via NHTSA static.nhtsa.gov
Related codes
How Obie handles P0456
Obie reads the EVAP codes and readiness, tells you what to check first, and tracks whether the EVAP monitor completes on later drives. Obie is part of ScanMyCar Pro. Codes and live sensors are free.
Questions people ask
Can a gas cap cause P0456?
Yes. A worn or loose gas cap is the most common cause. Tighten it until it clicks or replace it.
Is P0456 serious?
No. It does not affect how the car runs, but it fails emissions tests.
Why is P0456 so hard to find?
The leak is tiny. A shop smoke test is the reliable way to find it.
Sources
- RepairPal: P0456 code page repairpal.com
- RepairPal: Emission system diagnosis (shop) (updated September 3, 2026) repairpal.com
- RepairPal: Gas cap replacement (updated September 3, 2026) repairpal.com
- RepairPal: EVAP purge valve replacement (updated September 3, 2026) repairpal.com
- RepairPal: EVAP canister replacement (updated September 3, 2026) repairpal.com
- CarMD 2026 Vehicle Health Index (press release, April 22, 2026) prnewswire.com
- Infiniti EC13-015h via NHTSA static.nhtsa.gov
- Hyundai TSB 21-FL-002H via NHTSA static.nhtsa.gov
- Texas DPS emissions testing FAQ dps.texas.gov
- Arizona myazcar.com: OBD and the check engine light myazcar.com
A guide, not a diagnosis. This page describes what P0456 generally means across OBD2 cars. What is actually wrong with your car depends on its live data and its history, and any repair decision deserves a proper diagnosis, whether that is you with a scanner or a professional with a lift.