P0455 on a 2011 Toyota Sienna

P0455 means the EVAP system failed a leak check badly enough that the computer sees a large leak or no pressure/vacuum change.

Not your vehicle? See general P0455 info.

Most common causes on the 2011 Toyota Sienna

Ranked from 610 NHTSA owner complaints filed for this vehicle.

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1
EVAP pressure switching/vent valve stuck
Medium severity
A dealer diagnosed this Sienna's fuel emission (EVAP) pressure switch valve as stuck in the off position (P2440) — the same purge/vent hardware that governs P0442/P0455.
Reported in 1 NHTSA complaint
Parts:evap purge valve vent switching valve
2
Loose or faulty gas cap
Low severity
An owner was told to replace the gas cap after the VSC/check-engine lights came on for this same complaint pattern; check cap seal and threads first.
Reported in 1 NHTSA complaint
Parts:gas cap
3
Loose, damaged, or missing gas cap
Low severity
A cap left loose, cross-threaded, or missing entirely is the single most common trigger for a large EVAP leak (P0455); confirm it clicks fully closed and the seal isn't torn.
Common cause
Parts:gas cap
4
Cracked or disconnected EVAP hose/line
Medium severity
Rubber and plastic EVAP lines running between the tank, canister, purge valve, and intake harden and crack with age, or get knocked loose during other service work.
Common cause
Parts:evap hose evap line
5
Purge valve stuck open or leaking
Medium severity
A purge solenoid that doesn't seal lets outside air bleed into the system during the leak test, mimicking a real leak; a smoke test with the valve commanded closed will confirm it.
Common cause
Parts:purge valve
6
Canister vent (CVS) solenoid stuck open or clogged
Medium severity
The vent valve must seal the system for the PCM to pressurize/vacuum-test it; a stuck-open, corroded, or debris/ice-clogged vent valve causes a leak to be reported every time.
Common cause
Parts:vent valve canister vent solenoid
7
Cracked charcoal canister
Medium severity
The plastic canister housing can crack from age, road debris, or corrosion, producing a leak that only shows during the EVAP monitor.
Common cause
Parts:charcoal canister
8
Rusted or perforated fuel tank / filler neck
Medium severity
Road salt and age corrode steel filler necks and tank seams, opening a pinhole that leaks vapor (and eventually fuel).
Common cause
Parts:fuel tank filler neck
9
Faulty fuel tank pressure (FTP) sensor
Low severity
A drifting or failed FTP sensor can report a false leak even when the EVAP system is physically sealed; compare live sensor data against a known-good reading.
Common cause
Parts:fuel tank pressure sensor
10
EVAP leak detection pump/module failure
Low severity
On systems that use a dedicated leak-detection pump (or engine-off natural vacuum test) instead of engine vacuum, a weak or failed pump/module can't build the required test pressure and sets the code.
Common cause
Parts:evap leak detection pump

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These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0455 on your car still needs shop confirmation before any repair.

Common symptoms

Check engine light
Fuel smell
Usually no performance issue
Failed emissions readiness

What to check before replacing parts

Check the gas cap first

Look for: A loose, missing, or cross-threaded cap is by far the most common cause of a large EVAP leak code — if it doesn't click to full tightness or the seal is cracked, that's very likely the whole fault.

Inspect visible EVAP hoses

Look for: A large leak is often obvious: a hose disconnected at a fitting, split open, or chewed through (rodent damage is common) rather than a hairline crack.

Command the purge and vent valves with a scan tool

Look for: A valve that doesn't respond at all when commanded open/closed, or stays open when it should seal, prevents the system from holding pressure/vacuum and reads as a large leak.

Smoke-test the system

Look for: With a large leak, expect an obvious plume of smoke or a clearly audible hiss at the fault location — it should be easy to spot compared to a small-leak diagnosis.

Inspect the canister and filler neck

Look for: A cracked charcoal canister housing or a corroded/rusted-through filler neck (common on older vehicles) can leak enough to prevent the system from ever holding vacuum.

Rather have a pro handle it? Find a vetted local mechanic.

Matching symptoms

Check Engine Light