P0455 on Honda: How to Diagnose & Fix

P0455 indicates a large (gross) leak in the evaporative emission system — the PCM cannot build or hold EVAP vacuum/pressure at all. On the Honda Civic the two most frequent causes are strikingly simple: a gas cap that no longer seals (missing, loose, or a badly degraded O-ring) and the canister purge solenoid valve sticking open. On the 8th-gen (2006-2011) Civic the purge valve is mounted right on the intake manifold and a stuck-open valve is a documented failure. A stuck canister vent valve is another common source and can also cause a symptom drivers notice — difficulty pumping fuel / the pump clicking off early. On 10th- and 11th-gen (2016+, which use a capless fuel filler) Civics, the capless filler not fully closing after fueling has triggered P0455/P0456 EVAP leak codes.

P0442 sets when the Civic's PCM runs its EVAP self-test and detects a small leak (roughly 0.020-0.040 in). On 2006-2015 Civics the overwhelmingly most common source is the fuel-filler cap (2016+ Civics use a capless filler instead): the rubber O-ring on the cap hardens and shrinks with age/heat and stops sealing, which is why a P0442 frequently appears first and later escalates to a P0455 gross leak as the same gasket worsens. After the cap, the usual Civic culprits are cracked/perished EVAP vapor hoses (heat-aged rubber near the engine bay and along the tank), a purge solenoid or canister vent valve not sealing, or a leaking charcoal canister. It is common across all EVAP-equipped generations but very typical on high-mileage 8th-gen (2006-2011) and 9th-gen (2012-2015) cars.

P0455 is the large/gross EVAP leak code on the CR-V and points to a big open path in the fuel-vapor system. The most frequent CR-V causes are a missing, cross-threaded, or aftermarket gas cap that will not hold vacuum; a corroded or damaged fuel filler neck/main flap where the cap seals (a rust-belt problem on older Gen2/Gen3 CR-Vs); and the canister vent solenoid at the rear of the vehicle, which sits near the charcoal canister and is exposed to road salt and debris so it sticks open and never seals during the self-test. Cracked or disconnected EVAP hoses to the canister can also throw it.

The EVAP canister purge control solenoid on the intake manifold sticks open, throwing evaporative-system codes — commonly P0496 (EVAP flow during a non-purge condition), P0441 (incorrect purge flow), or a large-leak P0455 — and causing rough idle, hard/rough starts right after refueling, and a faint fuel smell. A worn or non-OEM gas cap is the first thing to rule out for P0455; if a genuine cap doesn't clear it, the purge valve is the usual culprit. The under-car vent solenoid at the charcoal canister is a secondary leak source from corrosion.