P0455 means the PCM could not pull or hold the expected vacuum/pressure during the EVAP self-test. A loose cap is possible, but an open purge or vent valve, disconnected hose, canister/tank leak or biased pressure sensor can look identical. Record the cap's found condition, fuel level and recent fuel-pump/body work. Command purge and vent, watch tank pressure and introduce approved low-pressure smoke. Honda bulletin 14-010 provides a software-update branch for all 2012 Accords and narrow early 2013 VIN ranges with P0455/P0456. It does not apply to a 2011, later-production 2013 or newer Accord simply because the code matches.
Match the symptom
Select the closest observation. The result changes the first test; it does not name a part to replace.
Record cap position and inspect its seal/filler surface before tightening.
What can set P0455—and how to separate it
The order below is evidence-driven, not a universal probability ranking. Vehicle year, repair history, companion codes and the operating condition in freeze frame change where diagnosis should begin.
| Possible cause | Evidence that supports it | First useful test |
|---|---|---|
| Cap missing, loose, damaged or wrong | Found condition or failed cap/filler sealing test | Inspect and pressure/vacuum test cap interface |
| Purge valve stuck open | Intake vacuum reaches EVAP when purge is commanded off | Closed-state sealing test |
| Vent valve open or large hose disconnection | System cannot seal and smoke exits | Bidirectional command and smoke test |
| Canister, tank or pump-module seal leak | Localized smoke/pressure decay, often after service | Sectional low-pressure test |
| PCM software branch on exact 2012–2013 vehicles | VIN/calibration matches 14-010 after physical checks | Honda bulletin applicability/calibration check |
Honda's 14-010 branch is software, not a universal leak repair
The bulletin covers defined 2012 and early-production 2013 vehicles. Confirm VIN and current PGM-FI calibration before programming.
A vehicle outside applicability still needs a physical leak/valve/sensor diagnosis. A software title cannot seal a disconnected hose.
The cap's found condition is perishable evidence
If the lamp followed refueling, note whether the cap was loose, cross-threaded or obstructed. Tightening before recording removes a likely explanation.
Inspect the filler neck as well as the rubber seal. A good cap cannot seal against a damaged or contaminated surface.
A normal passage can imitate a giant hole
The system must close purge/vent paths during portions of the test. A valve held open lets pressure escape without any cracked tank.
Command and verify actual sealing before replacing the canister. Electrical operation and mechanical sealing are separate questions.
Save these scan-data clues
Freeze frame is a snapshot of conditions when the PCM matured the fault. It can distinguish an idle-only problem from a load, cold-start or monitor-completion problem. Clearing first throws that context away.
- Fuel level and ambient/soak temperature
- Fuel-tank pressure sensor data
- Purge and vent command state
- P0456/P0441 or circuit companion codes
- Cap found condition and recent refueling
- Fuel-pump, tank or rear-collision repair history
A practical diagnostic workflow
- 01Preserve cap and freeze evidence
Do not erase the refueling condition by automatically tightening first.
- 02Check 14-010 by exact VIN
All 2012 are listed, but 2013 coverage stops at published early-production VINs.
- 03Test purge and vent sealing
A solenoid click does not prove the valve closes.
- 04Smoke-test at approved pressure
Inspect filler, hoses, canister and top-of-tank connections safely.
- 05Validate tank-pressure response
A biased sensor can misreport a leak even when the system seals.
- 06Complete the monitor after repair
Meet fuel-level/temperature/soak conditions and confirm no pending P0455.
Do not buy a cap and canister together. Each sealing point and valve can be tested. Do not perform a software update based on title alone; bulletin 14-010 has exact year/VIN applicability and requires approved Honda programming procedures.
Why the model year changes the test
Accord diagnostics span older F-series four-cylinders and J-series V6 engines, K-series four-cylinders with rocker-arm oil-pressure monitoring, Earth Dreams direct-injection engines, 1.5L and 2.0L turbo powertrains, and multiple hybrid generations. Cylinder/bank layout, VTEC/VTC oil control, EVAP strategy, catalyst monitoring and fuel delivery differ. Confirm model year, VIN, engine, transmission, hybrid status, emissions label and current Honda bulletin/campaign eligibility before choosing a test or part.
- 2012 Accord: all trims/VINs are listed in bulletin 14-010.
- 2013 Accord: only the published early-production four-cylinder and V6 VIN ranges are listed.
- Older P1456/P1457 Honda EVAP strategy and later generic P0455 systems should not be mixed.
- Hybrid and conventional models may package the tank/canister differently; use the VIN-correct schematic.
P0455 FAQ
Is P0455 always a loose gas cap?+
No. Valves, hoses, canister, tank seals and pressure sensing can all create a large-leak result.
Does bulletin 14-010 cover every 2013 Accord?+
No. It lists narrow early-production VIN ranges.
Can I drive?+
Usually briefly if no odor or wet fuel exists; stop for evidence of liquid leakage.
Can a purge valve cause hard starting?+
Yes. Vapor entering the intake while the valve should be closed can disturb a post-refuel start.
Can I use compressed air?+
Not directly. Use approved, regulated low-pressure EVAP equipment.
Why did a new cap not help?+
The leak or open valve may be elsewhere, or the filler sealing surface may be damaged.
Why will the monitor not run?+
Fuel level, soak time, temperature and other DTCs control enable conditions.
What confirms repair?+
Correct valve/pressure behavior and a completed EVAP monitor without pending P0455.
Ford diagnostic references
These documents explain Ford monitor operation. Exact pinpoint tests, connector views and specifications must be selected for the truck's VIN and model year in current service information.
01Honda Service Bulletin 14-010 — Accord P0455/P0456 softwareAll 2012 Accords and narrowly listed early-production 2013 Accord VINs; check exact applicability and current program status↗02Honda ServiceExpress technical informationHonda's service publications, wiring information and model/year repair procedures↗03Honda Accord authorized manualsHonda directs owners and technicians to ServiceExpress for electronic service publications↗