I have a 2002 Quad Cab with the 4.7L. I am trying to register my truck for the year, but my check engine light just came on. I changed the gas cap and reset the code (P0455), but two days later the light came back on. I have found that P0455 is a large leak in the EVAP system, and the main culprit is usually the gas cap, but in this case its obviously not. I can't tell a difference when driving it, but I don't think that it will pass emissions and inspection with a check engine light here in Utah (if anyone can confirm that, that would be great) . So I guess I'm just trying to find out any other obvious things it could be. I have looked under the hood and I can't find an obvious leak in a vaccuum line or anything. Anyone have any ideas? I'm really trying to avoid spending a fortune on this. Thanks in advance.

 

some shops can do a test on it i believe they fill the system with smoke so you can see where its leaking from but possibly dry rotted hoses

 

crawl under the cab and look for this:the hoses are probaly rotted. if you dont have emissions testing dont bother with it. I have had the same code as you for over a year and no issues.

 

check the evap hose in the engine bay its going to have a test port on it i had the same leak and it was coming from there cause the hose crack alittle and opened up. all i did was cut the hose back a little and reconnected it to the barb. if u need a pic of it let me know and i will take one and post it.