my scanner shows that as evap emissions leak(large leak detected) that would be tough to find unless you see large cracks or broken fuel lines,seperated evap lines and things of that nature.a mechanic with a smoke machine could find the leak and thats probably what you'll have to do to get it fixed.
P0455 - EVAP LEAK MONITOR LARGE LEAK DETECTED
This symptom is diagnosed using the test P0442 - EVAP LEAK MONITOR MEDIUM (0.040) LEAK DETECTED.
Immediately after a cold start, with battery/ambient temperature between 40 °F - 90 °F and coolant temperature within 10 °F of battery/ambient temperature.
There is a leak larger than 0.080" in the evaporative system.
* Confirmed leak in the EVAP system
* Intermittent LDP monitor failure