I can't specifically answer your questions as I am not technical but here is some info from the 2011 WK Factory Service Manual:
(ignore if not helpful)
P0455-EVAP PURGE SYSTEM LARGE LEAK
Theory of Operation
The Evaporative Purge Monitor tests the integrity of the hoses/tube between the throttle body/intake and the fuel tank. The monitor is a two stage test and runs only after the Evaporative system passes the small leak test. Stage one is non-intrusive. The Powertrain Control Module (PCM) monitors the purge vapor ratio and the Evaporative System Integrity Monitor (ESIM) Switch closed ratio. If the purge vapor ratio is above a calculated value, the monitor passes. If the ESIM Switch closed ratio is greater than calculated value when purge flow is greater than a minimum value, the monitor passes. Stage two is an intrusive test and runs only if stage one does not pass. The PCM commands the purge solenoid to flow at a specified rate to force the purge vapor ratio to update. The ratio is compared to a calibrated specification. If it is less than specified, a one trip failure is recorded. This test can detect if the purge hose is off, obstructed or the purge valve is not operational.
With the engine running, during a cold start test with the fuel level above 12%, ambient temperature between 4° C and 32° C (39° F and 89° F) and the fuel system in closed loop. The test runs when the small leak test is maturing.
The Powertrain Control Module (PCM) activates the Evap Purge Solenoid to pull the Evaporative system into a vacuum to close the ESIM Switch. Once the ESIM Switch is closed, the PCM turns the Evap Purge solenoid off to seal the Evaporative System. If the ESIM Switch reopens before the calibrated amount of time, a large leak error is detected. Two Trip Fault. Three good trips to turn off the MIL.
EVAPORATIVE PURGE SYSTEM LEAK
EVAP PURGE SOLENOID
EVAPORATIVE SYSTEM INTEGRITY MONITOR SWITCH
Note: A loose gas cap could have caused this DTC to set. Make sure gas cap is tight and in good condition. Make sure the gas cap meets OEM specifications.
Jeep Social Care Specialist