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Severity: Low Code type: Generic (all makes)

P0455 Code: EVAP System Leak Detected (Large Leak)

The fuel vapor system can't hold vacuum at all — check the gas cap first, then hoses and valves.

Safety first · Consult a professional

  • Fuel vapor is flammable. No smoking or open flames; work outdoors and fix fuel leaks before driving.

At a glance

Severity: 2/5 – Low2/5

Severity: Low

Meaning
EVAP System Leak Detected (Large Leak)
System
Emission Controls · Powertrain
Safe to drive?
Yes, short term
Typical repair cost
$15–$800
DIY difficulty
Easy

During the EVAP leak test the ECU closes the canister vent valve, opens the purge valve so engine vacuum is drawn into the tank, and watches the fuel tank pressure sensor. If vacuum barely builds within the allowed time, it records a gross leak: roughly the size of a missing gas cap. Unlike P0457, the ECU doesn't tie it to refueling, and unlike P0442 or P0456, you're looking for something big and usually easy to find with smoke. A purge valve stuck closed, or a blocked purge line, looks exactly like a large leak on this type of test, because no vacuum can reach the tank. Vehicles that run the test with the engine off use a small pump instead, and there a purge valve stuck open counts as the leak.

Can I keep driving? Safe to drive, but don't ignore it. If you smell raw fuel inside or around the car, park it outdoors, keep sparks and flames away and have it inspected soon.

How to read P0455

How to read P0455P10243554
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 4 Auxiliary emission controls
  4. 55 Specific fault

Symptoms

  • Check engine light on, not necessarily after refueling
  • Fuel smell around the car, especially near the rear or after parking in the sun
  • Pump nozzle clicking off early if a vent-side hose is kinked or the canister is saturated
  • Hissing or whoosh when opening the gas cap if the vent valve is stuck closed
  • Otherwise no change in how the car runs

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Gas cap loose, missing, the wrong type or with a failed seal 30%
  2. Canister vent valve stuck open from dirt, water or corrosion 18%
  3. EVAP hose or filler-neck vent line disconnected or cracked through 17%
  4. Purge valve stuck closed or purge line blocked (engine-running tests); stuck open on engine-off pump tests 13%
  5. Cracked charcoal canister or rusted-through filler neck 12%
  6. Faulty fuel tank pressure sensor or leak detection pump 10%

Diagnosis step by step

Diagnostic flow: P04551Rule out the cap2Visual check of the large hoses3Run the EVAP service test4Bench-check the purge and ventvalves5Smoke test the system6Verify the tank pressure sensor

  1. Rule out the cap

    Tighten the cap until it clicks, inspect the seal and swap in a known-good cap if in doubt. It's the cheapest fix and the most common one, but if the code returns with a good cap, stop replacing caps.

    Tools: Flashlight

  2. Visual check of the large hoses

    Follow the purge line from the intake to the canister and the lines from the canister to the tank and filler neck. Look for hoses knocked off during other work, rotted rubber sections and connectors that have popped loose.

    Tools: Flashlight

  3. Run the EVAP service test

    Many scan tools can close the vent valve and open the purge valve on command. Watch fuel tank pressure: it should drop to a few inches of water vacuum quickly and hold. No change at all means purge isn't flowing or the vent is open; vacuum that builds and collapses points to a large leak.

    Tools: OBD-II scanner

  4. Bench-check the purge and vent valves

    The purge valve should block air unpowered and open when energized; the vent valve should pass air unpowered and seal when energized. Check each coil for continuity and listen for a click when commanded.

    Tools: Multimeter, Vacuum gauge

  5. Smoke test the system

    Connect an EVAP-rated smoke machine to the service port (often a green cap under the hood) or the filler neck, with the vent valve commanded closed. Large leaks show smoke within seconds; check the filler neck, canister and tank top.

    Tools: Smoke machine, Flashlight

  6. Verify the tank pressure sensor

    With the cap removed, the sensor should read about zero on the scan tool. A reading stuck well away from zero, or one that doesn't move during the service test, points to the sensor or its wiring.

    Tools: OBD-II scanner, Multimeter

Where the parts are

EVAP system: gas cap, canister, purge and vent valves – P0455123456
EVAP system: gas cap, canister, purge and vent valves
  1. 1Gas cap
  2. 2Charcoal canister
  3. 3Purge valve
  4. 4Vent valve
  5. 5Fuel pump
  6. 6Intake manifold

Repair options & costs

RepairDIY?Estimated cost
Replacement gas cap Yes $15–$45
Reconnect or replace EVAP hose Yes $50–$300
Replace canister vent valve Yes $120–$350
Replace purge valve Yes $100–$300
Replace charcoal canister or filler neck No $300–$800

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Chevrolet

On Silverado, Sierra and other GM trucks and SUVs, the canister vent solenoid sits under the vehicle near the canister and is exposed to mud and water; a sticking vent solenoid is a frequent cause of P0455 and P0446 on these trucks.

P0455 on Chevrolet in detail

Ford

On Fords with the capless Easy Fuel filler, a dirty or damaged filler flap can let the system leak like a missing cap. Clean the flap area before replacing EVAP components.

P0455 on Ford in detail

Field data

Chevrolet 9
Ford 6
Hyundai 5 Sonata, Santa Fe, Sonata Hybrid
Chrysler 3 Aspen, Pacifica, Town And Country
Honda 3 Civic Hatch Type-R, Cr-V, Hr-V
Kia 3 Soul Ev
Mazda 3 Mazda3, MX-5/ MIATA, Tribute
Dodge 2 Caliber, Durango

Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.

Emissions / smog test impact

Will fail

An active P0455 with the check engine light on fails OBD-based smog and emissions tests. The EVAP monitor is often the slowest to complete after a repair, so allow several days of normal driving, including overnight cold starts, before retesting.

Frequently asked questions

My gas cap is new — why do I still have P0455?

Then the leak is elsewhere or a valve isn't doing its job. A vent valve stuck open, a disconnected hose, or a purge valve that won't open are the usual suspects, and a smoke test finds them quickly.

Can a bad purge valve cause P0455?

Yes. On systems that test with engine vacuum, a purge valve that won't open means no vacuum ever reaches the tank, which the ECU reads as a large leak. On systems that test with the engine off, a purge valve that won't close creates the leak itself.

Is a fuel smell with P0455 dangerous?

Fuel vapor is flammable, so treat a strong smell seriously: park outside, don't smoke near the car and get it checked soon. A faint smell near the filler after a fill-up is less urgent but still worth fixing.

How much does a smoke test cost?

Most shops charge about one hour of diagnostic labor, roughly $100–$200. For a large leak it's usually money well spent, because the leak is often visible within a minute.

Sources