I know this is a talked about topic and i have read a ton of posts but everyone seems to have found a fix replacing one of the items below except for me.

My engine light is on and throwing a P0455 code. So far i have replaced

Fuel pump
vapor canister
Purge valve
Gas Cap
Canister vent valve solenoid(hoses included)
and of course some lucas oil along the way


I just took it to a mechanic yesterday who reset the code and couldn't get it to trigger again. He even did a smoke test and found nothing. 5 miles down the road taking it home the light came back on. Any have any thoughts on what it could be?

 

the dtc is for a large leak.


the long list of parts replaced helps rule out some stuff.
What is the ftp sensor reading with the fuel cap open. Install the cap, start and idle the engine, close the vent valve and open the purge....watch the ftp reading...does it change?


did your mechanic hook the smoke machine up at the fuel filler neck to run his tests. I have the proper gm gas cap and filler neck adaptor and smoke test at the filler neck. I get much better results there than using the evap service port. I have seen leaks at the filler neck.

 

It sounds like i need a scanner to get the readings. I am great with mechanical things on cars but have no clue on electronics.

I have a call into the mechanic to find out about the smoke test.