My Check engine light came on this morning, so I pulled the code; P0455
(05 SS monte)

I found this info on the net:
{
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.
}

Suggested solutions are:
{
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)
}

I checked my gas cap; and reset the code & it came back on. I have heard of other spending $$$ for a smoke test... Have any of you guys run across this?

 

I found this on google......
Please note that a loose gas cap is not the only possible cause, but it is certainly the most likely. It could also be a cracked or loose hose, faulty gas tank seams, or anything else that may cause a large leak in the sealed EVAP system. A thorough visual inspection will often reveal loose hoses and lines.

 

that info also is the same for a p0440 code

 

Finally got around to checking this out; took a look under the hood and there you have it: (I reset codes after putting a new hose on, I also through a long term fuel trim code, assuming it's related, guess I'll find out after I drive a while)

 

Nice FIND!!! Thanks for sharing that. If I'm not mistaken, that is the hose for the EVAP purge solenoid? If so, I think on all GM v6 cars they went cheap on that hose, very thin rubber). Hmm, wonder if that is related to the wife's 3400 Impala with a P0440 (that hose is pretty thin, I think looking aged). I'll have to inspect!!

 

I had the same problem and replaced the line and now i have no code now. But my ECM will not run the EVAP diagnostics. I have driven for 2 days and not let eh gas go below a 1/4 thank not over 1/2 a tank about 150 miles now. The engine temp is normal also. on the dash gauge about one graduation below center. The car is a 2005 SS Monte Carlo. How can i get this to do its selftest or whats keeping it from running. Checked i have no codes or pending codes. The car is running great. No idea how to get it to do the selftest.

Scott