Need help with 2 codes. p0442, p0455

[SteveCZ28]

Ive had my 05 tahoe for a while now. but it seems like within the past 3 weeks Ive been having issues with it. it started throwing codes a few weeks ago. first time it was a p0442. guy at autozone said to tighten the gas cap. which i did (although when i fill i always tighten till it clicks about 3-5 times.) but he cleared the code and it was all good for the rest of that tank. so i fuel up last week, and truck gets down to around 3/4 of a tank, maybe a tad lower, and my check engine light comes on again. goto autozone to check it again, this time i have the following:
p0442 2 times
p0455 1 time.
he recommended buying a new gas cap (cap which i did)

i don't know where to start. i inspected the fuel cap when i took it off, o ring was still in good shape, couldn't see any dry rot or cracking. no debris on the fuel filler neck. but something is up if the truck is sensing a small and large leak.
the printout suggested a possible vacuum leak. but the engine runs smooth as can be, no hesitation or stumbling. i checked another thread for similar issues, and i don't have problems filling the tank. i always pump with the engine off (which is a no brainer) as the guy at autozone said that could throw the code too. so this is where i ask for help from the forums. as more minds are better than one on my situation.

 

[SteveCZ28]

can anyone give me an idea of what im looking for here? these same 2 codes came back yesterday.

 

[SteveCZ28]

now its telling me to tighten gas cap via the d.i.c

 

[Physh1]

I'd start here...

http://www.tahoeyukonforum.com/forum/showthread.php?t=16989

Cameron

 

[SteveCZ28]

i went ahead and replaced the canister vent valve solenoid. super easy removal and install. took cap off old canister and it was caked with dirt and dust, and some chunks as well. but installing this did not solve my issue. still getting the same 2 codes. i visually inspected all the lines and connections while i was under the truck, and didnt notice anything out of the ordinary. nothing looked wet or moist from fuel either. so im back to square one, what do i do now?

 

[Physh1]

I know those codes tend to be pretty hard to solve. I'll see what else I can dig up...

You did clear the codes first right? They popped back up?

Cameron

 

[SteveCZ28]

I know those codes tend to be pretty hard to solve. I'll see what else I can dig up...

You did clear the codes first right? They popped back up?

Cameron

correct. installed the solenoid. went and had codes cleared. made it about 10 miles ses came back on, turned around and had codes checked again, and same 2 popped back up.

 

[SteveCZ28]

ironically the other mornin on my way home from work, the ses light went out on its own. so i made a trip had codes pulled again, although the same 2 codes were still stored, they were inactive. so he cleared them again. still no ses. hopefully im done with that problem