'07 Suburban p0455 but "no" leak

[mag68]

I have a 2007 Suburban that is a 5.3L flex fuel with active fuel management. The check engine light has come on with code p0455, "mass evap system leak". I took it to a shop and they ran a smoke/pressure test with the motor hot and cold. It passed both tests. They replaced and moved the vapor canister vent solenoid, but that didn't help. I'm about to sell this vehicle and wanted to fix this issue for the prospective buyer. Are there any cheap, and relatively easy ways to diagnose the bad component that is causing this code? I don't want to spend lots of money fixing the problem, but also don't want to try and sell a car that has a check engine light on. Any pointers on how to trouble shoot this would be appreciated!

[lowridergmc]

i have seen a few fuel tank pressure sensors reading incorrectly causing evap leak code.

[mag68]

Thanks lowrider! That's what I was thinking. I actually picked a sensor up a few days ago but haven't had time to put it in. I hope you are right. Seems like that would be the only other thing it could be. I'll post up the results a few days after I change it out.
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[4x4toy]

Double check the line between the vent solenoid and the fuel pump holer, if it looks greasy at the fuel pump holder it is leaking. Vent solennoid should have come with new line, I think. But double check, I will put slightly thicker O-ring when I replace them. Lube it so it does not roll when you connect it back together.
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[mag68]

4x4toy, thanks but there is NO leak. That's what is stupid! I had two smoke tests (that checks for leaks) and they also pressure tested the system. It held pressure and didn't "leak" any smoke out. I was hoping there was something easier to try but I'm going to drop the tank down and swap out the pressure sensor. If it's not that, it was only $35.
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[mag68]

So I changed out the pressure sensor and cleared out the code. I Drove it around town for a few days and thought it was fixed. During an hour long highway drive the stupid light came back on. Anyone have any other ideas?
Just to review, so you dont have to read previous posts-
*code is 0455 (mass evap system leak)
*there is supposedly not really a leak- it passed two pressure and smoke tests
*the vapor canister vent solenoid has been replaced and relocated
*the pressure sensor on the top of the tank has been replaced

I appreciate any help
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[mag68]

Well, if anyone cares or is having a similar problem, I replaced the purge solenoid and this appears to have fixed the issue. Apparently the solenoid was intermittently not working every once in a while thus setting the code/engine light. The issue was hard to diagnose even by the OBD2 machine (or whatever you call it) that can manually actuate each solenoid, valve, etc. Anyway, that was super annoying and took forever to figure out....but now it is fixed.

Just thought I would give some closure to this thread. I know many people use this website for help in researching and fixing their own vehicles.
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[HARLEY'S LIMO]

Hi. I am new to this, so please be patient with me. I have a 2007 Suburban that recently threw a po455 code after my check engine light came on. I changed the gas cap and resest it only to have it come back a cou ple days later. This continued for a few days. My low tire pressure light then came on. All tires were properly inflated. I still added a couple psi to even them out but could not make the light go out. The obd now shows both a po455 and po496, but nothing about the tires. Could this possibly be a computer malfunction? Any suggestionswould be greatly appreciated, as I can not afford a pricey mechanic bill...
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