P0456 EVAP system very small leak detected

EVAP very small leak (0.020 inch)

Monitor

EVAP faults let fuel vapour escape but rarely change how the car drives, and the main risk is a failed emissions test, so it is safe to drive while you arrange a fix.

It gets more serious if:

  • Inspect soon: You keep smelling raw fuel around the car, not just right after filling up
  • Stop: You see liquid fuel dripping or pooling under the car, or near the filler, tank or canister

Source: how we rate severity

P0456 in short

P0456 means the computer found a very small leak in the fuel vapour (EVAP) system, about the size of a pinhole. A worn fuel cap seal is the first thing to check, then cracked hoses or a valve that does not seal. It is safe to drive unless you smell fuel strongly.

The EVAP system holds fuel vapour so it can be burned instead of escaping. The computer seals the system and checks whether it holds vacuum or pressure. Regulations require it to catch leaks down to about 0.020 inch across, and P0456 is the code for the smallest leak size.

Some systems, such as Toyota pump-based designs, compare the leak against a built-in 0.020 inch reference hole with the engine off. If the system leaks more than that hole, it sets P0456.

Leaks this small are hard to find. A shop usually needs a smoke test, and some leaks only show under vacuum, so a clear smoke test does not always end the search.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Loose, damaged or non-factory fuel cap

    Common general cause
    Why it ranks here
    A cap whose seal is slightly worn, cut or rolled can leak just enough to set the smallest leak code. It is the cheapest thing to rule out.
    What would change this
    Falls if the cap is factory, clicks and the seal is clean and flexible.
    How to test the fuel (gas) cap

  2. Split, cracked or disconnected EVAP hose

    Common general cause
    Why it ranks here
    Fine cracks in ageing hoses make small leaks, and FCA has a bulletin naming a split purge hose for P0456.
    What would change this
    Rises if smoke appears at a hose or fitting.
    How to test the vacuum hoses and intake leaks

  3. Canister vent valve that does not seal, or is fouled by dust

    Possible — needs testing
    Why it ranks here
    Vent valves can leak under vacuum while sealing under pressure, which suits a tiny leak that is hard to find.
    What would change this
    Rises if the vent valve fails a vacuum check after a clean smoke test.
    How to test the evap canister vent valve

  4. Purge valve leaking or not opening when commanded

    Possible — needs testing
    Why it ranks here
    A purge valve that seeps when closed can register as a small leak. VW lists P0456 among purge-valve codes.
    What would change this
    Rises if the valve passes vacuum when commanded closed.
    How to test the evap canister purge valve

  5. Filler neck or cap seat not sealing

    Possible — needs testing
    Why it ranks here
    Damage at the filler neck where the cap seals can leave a tiny gap.
    What would change this
    Rises if a new cap does not cure it and the neck lip is damaged.
    How to test the fuel (gas) cap

  6. Leaking or contaminated charcoal canister

    Possible — needs testing
    Why it ranks here
    A pinhole in the canister is possible but less likely.
    What would change this
    Only confirmed by smoke at the canister body.
    How to test the evap charcoal canister

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Remove and refit the fuel cap. Check it is a factory or OEM-equivalent cap, that it clicks when tightened, and that its seal is not cut, cracked or rolled.

    Low risk

    • IfThe cap was loose, missing, non-factory or has a damaged seal

      It meansThe cap is the most likely leak. Tighten or replace it and let the system re-check over the next few days.

      Points to: Loose, damaged or non-factory fuel cap

    • IfThe cap is factory, clicks and the seal looks good

      It meansLook further along the system.

      Go to step 2

  2. Read all stored and pending codes with a scan tool and note which other EVAP codes are present.

    Low riskTool: OBD-II scan tool

  3. With the engine off and cool, look over the EVAP hoses and connectors you can reach at the purge valve, the canister and the filler neck.

    Use cautionTool: flashlight

    Warning:Fuel vapour is flammable. Work outdoors with the engine off and cool, and keep sparks, cigarettes and open flames away.

  4. Have a shop smoke test the EVAP system with the vent side sealed and look for smoke escaping.

    Best left to a shopTool: EVAP smoke machine

    Warning:Shop test. The setup has to match how the system is tested (pressure or vacuum), and fuel vapour is flammable.

  5. Have the shop command the vent and purge valves with a scan tool and check each one holds vacuum with a hand vacuum pump.

    Best left to a shopTool: scan tool with output controls, hand vacuum pump

    Warning:Shop test on the fuel vapour system.

Symptoms

  • Check engine light on, usually with no change in how the car drives
  • Fails an emissions or smog test because of the light or an incomplete EVAP monitor
  • Persistent raw fuel smell around the car Gets more serious: stop and have it checked.
  • Liquid fuel dripping under the car Gets more serious: stop and have it checked.

Compare with: Check engine light came on after getting gas

How to fix

  1. Check the fuel cap is a factory or OEM-equivalent part, then tighten it until it clicks.

    Warning:Engine off, no smoking or flames near the filler.

  2. Look at the cap seal for cuts, cracks or a rolled o-ring and replace the cap if it is damaged.

  3. Stop filling once the pump clicks off the first time. Topping off can flood the canister.

  4. After a repair, drive normally for several days so the monitor can re-run. Clearing codes or disconnecting the battery resets readiness, so do it shortly before an inspection only if you then complete a drive cycle.

Parts and cost context

  • Fuel (gas) cap:A factory or OEM-equivalent cap is the cheapest first step. Toyota, for example, says to use only a genuine cap.
  • EVAP charcoal canister:Replace the canister only after a smoke test confirms it is leaking. Labour varies, so get a quote.
  • EVAP canister vent valve:Often mounted near the canister or tank. Labour varies, so get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Jeep

  • 2015 · Grand Cherokee

    Supported by vehicle data

    FCA bulletin 25-002-15 REV. A links P0455 and P0456 on vehicles built 16 Nov 2014 to 17 Jan 2015 to a split hose at the purge valve. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

    Where it is:Hose at the purge valve

    NHTSA owner complaints mentioning P0456: 10. That shows what owners reported, not how often a cause sets the code.

  • 25-002-15Status unverified

    P0455 and/or P0456 from a split purge valve hose

    2015grand-cherokee · issued · rev. REV. A · NHTSA MC-10151727

    On vehicles built 16 November 2014 to 17 January 2015, the hose at the purge valve can split and set large or small leak codes. Replace the hose. The bulletin also covers the 2015 Dodge Durango built in the same window.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Dodge

  • 2015 · Durango

    Supported by vehicle data

    The same FCA bulletin (25-002-15 REV. A) covers Durangos built in the same window for P0455 and P0456 caused by a split purge valve hose. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

    Where it is:Hose at the purge valve

  • 25-002-15Status unverified

    P0455 and/or P0456 from a split purge valve hose

    2015grand-cherokee · issued · rev. REV. A · NHTSA MC-10151727

    On vehicles built 16 November 2014 to 17 January 2015, the hose at the purge valve can split and set large or small leak codes. Replace the hose. The bulletin also covers the 2015 Dodge Durango built in the same window.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • P0455EVAP system large leak detected

    Same system Common general cause

    Same leak test, larger leak. A completely loose cap or a disconnected hose sets P0455; a slight seep sets P0456. Toyota pump systems decide between them with the same reference hole.

  • P0442EVAP system small leak detected

    Same system Common general cause

    P0442 is the next leak size up. Both come from the same leak monitor and share the same likely causes.

  • P0446EVAP vent control performance problem

    Same system Common general cause

    P0446 is a vent control code. If it or P0449 is stored with P0456, the vent valve or vent path is a strong suspect.

  • P0441EVAP purge flow incorrect

    Same system Common general cause

    P0441 is a purge flow code. If it or another purge code is stored with P0456, start at the purge valve and its hoses.

All EVAP (evaporative emissions) codes

P0456 questions

Can a loose gas cap really cause this code?

Yes. OBD systems can detect the vapour leak from a cap that is not tightened. After you tighten or replace it, the light should go out by itself once the system re-checks and passes on later drives, which can take several trips.

Why can a shop not find my P0456 leak?

Leaks this small are hard to see. Some only open under vacuum, so a pressure smoke test can miss them, and some only appear when the parts are cold. The shop may need to test the valves under vacuum one by one.

Is it safe to keep driving?

Usually yes, as long as there is no strong fuel smell and no fuel dripping. Most makers advise getting it fixed when it is convenient. A strong fuel smell means get it checked soon, and dripping fuel means stop and do not drive.

Will this code fail an emissions inspection?

In states that test OBD-II, a check engine light that stays on with the engine running fails the test. Clearing the code does not help straight away, because the EVAP monitor then reads not ready until the car completes a drive cycle.

Sources and review

  1. Frequently Asked Questions on On-Board Diagnostics (EPA 420-F-97-003) — US EPA ,
  2. On-Board Diagnostic II (OBD II) Systems Fact Sheet — California Air Resources Board ,
  3. EVAP: The Phantom Emissions Menace (Nissan TechNews, May 2018) — Nissan North America (hosted by AutomotiveTechInfo) ,
  4. OBD Test Reference (rev 8.6) — California Bureau of Automotive Repair ,
  5. What do you mean my car is not ready? — New York State DMV
  6. Recall acknowledgement 17V-088: BMW i3 REx fuel tank vent line may chafe — BMW of North America / NHTSA
  7. Part 573 Safety Recall Report 15V-621 (Mazda 8615J): liquid fuel can enter the EVAP canister — Mazda North American Operations / NHTSA
  8. What To Do With the Check Engine Light (EPA420-F-00-041) — US EPA ,
  9. Toyota Camry Owner's Manual (OM06291U, 2.5L A25A-FKS / 3.5L 2GR-FKS) — Toyota
  10. FCA 25-002-15 REV. A: P0455 and/or P0456 from a split purge valve hose — FCA US / NHTSA ,
  11. GM PI0979: P0442 from a vent solenoid that leaks under vacuum — General Motors / NHTSA ,
  12. GM 23-NA-073: P0442, P0446, P0455 or P0449 from dust intrusion into the canister and vent solenoid — General Motors / NHTSA ,
  13. VW 20 17 02: EVAP purge valve (N80) diagnosis — Volkswagen of America / NHTSA ,
  14. GM PIC6030: P0442 from fuel filler pocket insulator rolled over the filler neck — General Motors / NHTSA ,
  15. GM 22-NA-217: P0442 from a purge canister weld leak — General Motors / NHTSA ,
  16. Driveability Corner, August 2014 (Mark Warren) — MOTOR Magazine ,
  17. Cal. Code Regs. Tit. 13, § 1968.2 — Malfunction and Diagnostic System Requirements (OBD II) — California Air Resources Board (via Cornell LII)
  18. NHTSA ODI consumer complaints flat files — National Highway Traffic Safety Administration (NHTSA), Office of Defects Investigation
Last reviewed
Written by
Saurabh K.
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