you are right, and i really should have tried it myself 1st.
the mechanic i use is next door to my work so it's easy for me to let him do it, but i think even he was a little surprised that i didn't do it myself.

been a day and so far so good (knocking on wood)

 

glad you got it fixed! seems to be a chevy problem lately. not only do i see it all the time on montes and impalas (i work at autozone and spend probably half my day reassuring people their check engine light does not mean their car is going to explode) but i just changed a vent valve on my dads z06. what the heck chevy! atleast source some good ones for your flagship car!

 

My 06 Silverado had the same problem. It has been reported that it is caused by overfilling your tank or filling it while the vehicle is running.
This causes the gas to be sucked in the Vent Valve. once it gets saturated your light comes on. That's why it comes and goes until it won't go off at all.

 

this is interesting! ill have to make sure i dont overfill it anymore, i just like putting in all it can take one because i try to minimize gas trips and two because i like it to stay at full longer lol

 

Did mine the other day! I'm not sure if it was the vent or the gas cap. I changed both. Good to go!

 

Nope, they are just junk. C/K bodies, and w-bodies have a pretty high failure rate. Usual code I see is P0449 or P0455

 

Does a bad Vent valve affect gas mileage or performance in anyways?

 

I have the same problem with mine and i have a 06 and i was told i had to drop the tank so you are probley going to have to do the same sorry

 

You DO NOT have to drop the tank for the valve on your '06. Just look up from under the rear of your car near your fill tube and you will see it. It takes one 10mm bolt and a spring clamp. VERY easy.

 

^^ this. you dont even have to take the wheel off, super easy!