The P0455 code in your 2018 Honda Accord appearing after a fill up is a common scenario. P0455 indicates a gross (large) leak in the EVAP (Evaporative Emission Control) system. When this happens specifically after fueling, the cause is usually simple—the gas cap wasn't properly secured or has a faulty seal.
Why Fill Up Triggers This Code
The EVAP system controls fuel vapors and must be sealed. After filling, the system runs a leak test. If the gas cap isn't clicked tight or has a damaged seal, the system detects the opening as a large leak and triggers P0455. This is the most common cause of post-fill-up EVAP codes.
The Capless Fuel System
The 2018 Accord uses a capless fuel filler—there's no traditional gas cap. Instead, a spring-loaded flap seals the filler neck. P0455 can occur if this mechanism doesn't seal properly, if debris prevents closure, or if the fuel nozzle damages the flap.
Common Causes
Debris preventing capless filler from sealing. Damaged capless filler door/flap. Nozzle damage to the capless system. Actual EVAP system leak elsewhere (less common after fill-up timing). Fuel overfill affecting system pressure.
Solution Steps
Inspect the capless filler for debris, damage, or stuck flap. Clean the filler area and ensure the flap moves freely. Clear the code and drive through a few cycles. If code returns without additional fill-up, a real EVAP leak exists elsewhere. If it only appears after fueling, the filler mechanism is the issue.