- Vehicles
- Cars
P0456
P0456 (generic OBD-II): very small leak in the EVAP system
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Low
Quick answer
The EVAP test found a very small leak, about the size of a 0.020 inch hole. It does not affect driving, but it will not fix itself. Check the fuel cap and, if the code persists, ask for a smoke test.
Safety first
Stop and check this first
- If you smell petrol in or around the car, do not smoke, do not light anything and do not drive; call roadside assistance.
Safe checks you can perform
- Cap and seal
- Whether it returns after the monitor completes
- Petrol smell
Leave these tasks to a qualified professional
- Do not attempt this professional task: Full EVAP smoke test
- Do not attempt this professional task: Engine-off EVAP monitor data
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Full EVAP smoke test
What they doThe technician fills the EVAP system with smoke and works along the cap, filler neck, lines, canister and valves.
They must show youthe leak point in a photo or video.
In writingthe part replaced and its number, or that the smoke found no leak.
Engine-off EVAP monitor data
What they doThe technician reads the engine-off EVAP test results (mode 6 if the car provides them) and checks the vent valve and tank pressure sensor.
They must show youthe test result against its limit and the vent valve response.
In writingwhat was repaired and when the monitor completed with no code.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Cap and seal
- Who:
- you, with the engine off.
- How:
- remove the cap, check the seal is not cracked, clean the filler neck and close it firmly.
- Result that matters:
- whether the seal was damaged or dirty.
- If it was damaged or dirty:
- fix it and drive normally; the monitor needs several days to run again.
- If it was fine:
- this rules the cap out as the likely cause; a smoke test is next.
- Evidence to keep:
- a photo of the seal and the date of the check.
No flames or cigarettes when opening the tank.
Evidence: Ford 2020-2023 gasoline OBD system operation
Whether it returns after the monitor completes
- Who:
- you, with a generic OBD-II reader.
- How:
- without clearing the code, check the EVAP monitor status on the reader over the following days.
- Result that matters:
- whether the monitor completes and whether P0456 returns as confirmed.
- If the monitor completes and the code no longer shows as active:
- this confirms the fix worked.
- If the code returns:
- the leak is still there; a workshop smoke test is needed.
- Evidence to keep:
- photos of the monitor status and the codes on different dates.
Look at the reader only with the car parked.
Evidence: Ford 2020-2023 gasoline OBD system operation
Petrol smell
- Who:
- you, outdoors.
- How:
- check for a fuel smell around the tank or in the cabin.
- Result that matters:
- whether there is a persistent smell.
- If there is a strong smell:
- that does not fit a very small vapour leak; do not smoke, do not start the car and call for assistance.
- If there is no smell:
- this fits P0456; book a visit without urgency.
- Evidence to keep:
- whether there was a smell and where.
Evidence: Ford 2020-2023 gasoline OBD system operation
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Vehicles
- Brand
- OBD-II genérico
- Product type
- Cars
Known code variants
- P0456
- P0456 EVAP very small leak
- P0456 fuga muy pequeña EVAP
- P0456 OBD2
What it means
P0456 is the generic code for a very small leak in the EVAP system. California's OBD II regulation requires detecting leaks equal to a 0.020 inch orifice. In Ford's OBD summary this test runs with the engine off: after a drive it uses the tank's natural cooling and checks whether pressure or vacuum builds over up to 45 minutes. That is why the code can appear with no symptom at all. It does not say which part leaks.
Warnings and stop conditions
- Higheditorial warning
If you smell petrol in or around the car, do not smoke, do not light anything and do not drive; call roadside assistance.
Evidence: Ford 2020-2023 gasoline OBD system operation
Symptoms and causes
Probable causes · in order
- Fuel cap sealPossible
A hardened or dirty cap seal is enough for a leak this size. It shows if the code goes away after fixing it and completing the monitor.
Evidence: Ford 2020-2023 gasoline OBD system operation · Title 13, California Code Regulations, Section 1968.2, Malfunction and Diagnostic System Requirements (OBD II)
- Hose or joint with a fine crackPossible
FCA linked P0456 to a split purge hose on two 2015 models. Fine cracks only show with smoke.
Evidence: FCA TSB 25-002-15 Rev A Jeep Grand Cherokee P0455
- Vent valve or tank pressure sensorPossible
Ford needs the vent valve, tank pressure sensor and purge valve working for this test. A fault in them usually sets its own code.
Evidence: Ford 2020-2023 gasoline OBD system operation
Virtual technician
Does P0456 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
FCA TSB 25-002-15 Rev A Jeep Grand Cherokee P0455
FCA US LLC · 2015 · service_bulletin
- 2
Ford 2020-2023 gasoline OBD system operation
Ford Motor Company · 2023 · manual
- 3
California Air Resources Board · 2006 · official_doc
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