You can forget about P0422 when you have P0455: Evaporative Emission Control System Leak Detected (no purge flow or large leak)
What does that mean?
This indicates a fuel vapor leak or lack of purge flow in the EVAP control system. It means a large leak has been detected. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.
* A loose or improperly affixed gas cap
* A non-conforming gas cap (i.E. Not factory/original brand)
* Other leak or damaged piece in EVAP system
With a P0455, the most common repair is to: * Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
* Otherwise, replace the gas cap, and/or
* Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary
* Inspect EVAP system purge solenoid
*Inspect EVAP canister for broken hose or canister