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P0455 on a 2017 Honda Civic

EVAP Large or Gross Leak Detected

Severity: low Safe to drive (short term) Compact Sedan 2015-2019 Honda Civic

What does P0455 mean on a 2017 Honda Civic?

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.

Symptoms on a 2017 Honda Civic

Likely causes on a 2017 Honda Civic

  1. Missing, loose, or wrong-fit fuel cap Most common
    Estimated repair: $0– $60

    Always check first. A locking gas cap from another vehicle that almost fits is a common source.

  2. Disconnected or split EVAP hose Common
    Estimated repair: $30– $200
  3. EVAP vent valve stuck open (will not seal during the monitor test) Common
    Estimated repair: $80– $350
  4. Damaged or rusted-through fuel filler neck Occasional
    Estimated repair: $200– $700
  5. Cracked or broken EVAP charcoal canister Occasional
    Estimated repair: $200– $600
  6. Damaged O-ring at the fuel pump assembly cover Rare
    Estimated repair: $30– $500
  7. Rodent damage to EVAP hoses (parked vehicles) Occasional
    Estimated repair: $30– $200

How to diagnose this on a 2017 Honda Civic

  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

Known Technical Service Bulletins for the 2015-2019 Honda Civic

Manufacturers publish Technical Service Bulletins (TSBs) when a known issue affects a specific vehicle. These bulletins come from the NHTSA database for your Honda Civic.

+14 more TSBs available in MECH AI's TSB explorer for this vehicle.

Common fixes

About the 2015-2019 Honda Civic

The 2015-2019 Honda Civic was commonly sold with the following powertrains: 2.0L I4, 1.5L Turbo I4, 1.8L I4. Common trims include LX, Sport, EX, Touring.

How fast P0455 sets after a missing cap

Most OBD-II vehicles flag P0455 within one cold-start drive cycle after the cap is left off. Some Ford and GM vehicles will set a more specific “check fuel cap” message first and only escalate to P0455 if the issue persists across multiple drive cycles.

P0455 right after winter on a parked vehicle

Mice and rats chew EVAP hoses to nest inside the canister or near the fuel tank. If P0455 appears on a vehicle that has been parked for the winter, inspect every accessible EVAP hose for clean-edged bite marks before buying parts. This pattern is so common on rural-parked trucks that several shop forums have dedicated threads.

The cap that “fits” but doesn’t seal

A locking gas cap from a similar-vintage vehicle in the same brand family often threads on but seals against the filler neck at the wrong depth or angle. The result is repeated P0455 codes after every refuel. If the cap has been replaced and the code persists, double-check it is the exact OEM part number for this vehicle.

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