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P0455 — EVAP Large or Gross Leak Detected

P0455 is set when the EVAP system's gross-leak monitor detects an opening approximately 0.090 inches (2.3 mm) or larger — or in many cases, no seal at all. This is the size of a missing gas cap, a disconnected hose, or a failed vent solenoid stuck open. The system cannot hold pressure or vacuum for the calibration period, so the ECM concludes a major leak.

P0455 means evap large or gross leak detected. A vehicle usually stays drivable short-term with this code, but it should be diagnosed promptly. The most common cause is missing, loose, or wrong-fit fuel cap (typically $0–$60). Causes and cost vary by make and model; confirm the root cause before replacing parts.

Severity: low powertrain Safe to drive (short term)

Reviewed by MECH AI Editorial · Last verified

What does P0455 mean?

P0455 is set when the EVAP system's gross-leak monitor detects an opening approximately 0.090 inches (2.3 mm) or larger — or in many cases, no seal at all. This is the size of a missing gas cap, a disconnected hose, or a failed vent solenoid stuck open. The system cannot hold pressure or vacuum for the calibration period, so the ECM concludes a major leak.

What are the symptoms of P0455?

What causes P0455?

Cause Likelihood Estimated repair (USD)
Missing, loose, or wrong-fit fuel cap — Always check first. A locking gas cap from another vehicle that almost fits is a common source. Most common $0–$60
Disconnected or split EVAP hose Common $30–$200
EVAP vent valve stuck open (will not seal during the monitor test) Common $80–$350
Damaged or rusted-through fuel filler neck Occasional $200–$700
Cracked or broken EVAP charcoal canister Occasional $200–$600
Damaged O-ring at the fuel pump assembly cover Rare $30–$500
Rodent damage to EVAP hoses (parked vehicles) Occasional $30–$200

Repair costs are typical US ranges and vary by make, model, model year, and labor rate. A diagnostic trouble code is a symptom, not a guaranteed failed part — confirm the root cause before replacing anything.

Is it safe to drive with P0455?

In most cases a vehicle stays drivable for short trips with P0455 active, but you should diagnose and repair it promptly. This is a low-severity code — ignoring it can lead to further damage or a failed emissions test. Exact tolerance depends on your specific make and model.

How to diagnose P0455

  1. Check the gas cap is present and correctly seated

    Confirm the cap is the correct OEM cap for the vehicle. Many generic-fit replacement caps look identical but have slightly wrong gasket geometry. Hand-tighten to at least 3 clicks. Some vehicles flag a missing cap as P0455 within one drive cycle.

    Tools: None

  2. Visually inspect the EVAP hoses near the canister

    On most trucks and SUVs the EVAP canister sits behind the rear bumper or above the rear axle. Inspect every hose from the canister to the tank vent and to the purge solenoid. Pay particular attention to rodent damage on parked vehicles.

    Tools: Floor jack and stands, Flashlight

  3. Smoke-test the EVAP system at low pressure

    Introduce smoke at 0.5 psi through the service port. With a large leak the smoke will pour visibly from the failure point within seconds. If smoke escapes from the vent solenoid even with the solenoid commanded closed, replace the solenoid.

    Tools: EVAP smoke machine

  4. Test the EVAP vent valve function

    Disconnect the vent valve and apply 12 V — it should click and close. Hold a hand vacuum pump to one port and verify the valve holds vacuum when energized. A vent valve that does not close fully will set P0455 because the system can never seal.

    Tools: 12 V test source, Hand vacuum pump

  5. Inspect the fuel filler neck and tank-top seals

    Rust-belt vehicles often develop pinholes or seam separation in the metal portion of the fuel filler neck. Once the rust is through, the EVAP system cannot hold any vacuum. Replacement is the only fix.

    Tools: Floor jack and stands, Inspection mirror

How do I fix P0455?

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P0455: frequently asked questions

What does diagnostic trouble code P0455 mean?

P0455 is set when the EVAP system's gross-leak monitor detects an opening approximately 0.090 inches (2.3 mm) or larger — or in many cases, no seal at all. This is the size of a missing gas cap, a disconnected hose, or a failed vent solenoid stuck open. The system cannot hold pressure or vacuum for the calibration period, so the ECM concludes a major leak.

What are the symptoms of P0455?

Check Engine Light is illuminated. Distinct fuel smell, especially after refueling. Fuel-cap warning message on the dashboard on some vehicles. No drivability issue. Vehicle will fail emissions / smog testing

What causes P0455?

Missing, loose, or wrong-fit fuel cap (most-common). Disconnected or split EVAP hose (common). EVAP vent valve stuck open (will not seal during the monitor test) (common). Damaged or rusted-through fuel filler neck (occasional). Cracked or broken EVAP charcoal canister (occasional). Damaged O-ring at the fuel pump assembly cover (rare). Rodent damage to EVAP hoses (parked vehicles) (occasional)

Is it safe to drive with P0455?

In most cases a vehicle stays drivable for short trips with P0455 active, but it should be diagnosed and repaired promptly — this is a low-severity code. Ignoring it can lead to further damage or a failed emissions test. Specific tolerance varies by make and model.