I have an 05 Tahoe and I have been haunted by a P0455 since I got it a few months ago. I'll run you through what I have done so far. I have hooked this up to a evap smoke machine so I know exactly where the leak is. It comes out the canister vent valve. Naturally, when I saw that, I installed a new one. The new one does the same thing. I tested both of them and they both actuate properly and seal completely.

I then hooked a Genisys scan tool to it and commanded the vent valve closed. Nothing. I went down to the plug for the valve, one wire is constant hot(the pink one i think) and the other(white) should be commanded a ground by the pcm to close, but it doesn't. I can manually close it with a power probe and the tank pressure sensor reads it builds up to about 5psi with the smoke machine on it, as it should, and no other leaks are seen.

So I know the fuel tank pressure sensor works. I know the vent valve works as its new. I know the purge valve works as it sealed to smoke it. I know the gas cap doesn't leak or I would have seen the smoke leak out of it. I know no other line/hose is cracked/broken or i would have seen it when I closed the vent valve.

I tried to trace the white wire back to the PCM but time constraints prevented. I did manage to find two white wires but was unable to see which one, if either, was the vent valve signal.

Providing I find the correct wire and there are no breaks in it. I am at a complete loss of what to do here. Any ideas?

 

Welcome to the forum.

Certainly sounds like a wiring problem from what you've described. Or the PCM is going bad, less likely tho.

 

I certainly hope it isn't a pcm issue. I'll let you know what i find, when/if i find it.