P0455 is LARGE leak and is generally not associated with a gas cap, unless the cap is left off completely. P0442 is a small leak and usually associated with a failed cap or gasket. P017X are fuel trim. Need to find out where that large leak is coming from. Could be a solenoid, bad line, etc. Dealer has a smoke machine (or should have one) that makes diagnosis of a leak very easy.

Also, there is a good chance the lean trim codes might fall under the 5yr/100K powertrain warranty, and the EVAP code should fall under an emissions warranty.

 

mjc3276,

I am sorry to hear that you are experiencing an issue with your vehicle. I might not be able to give any technical advice but I would like the opportunity to look into this for you. Please private me if I can be of any assistance.

Regards,

Jennifer T.
GM Customer Care

 

Thank yall for the guidance. I think I got it fixed. I had a P0305 code come up (as well as P0449 and P0455). That helped really hone in the issue as I went to put in a new plug, the stupid spark plug wire was off my #5 cylinder. Cleared the codes and put a 40 min ride on her... shes been behaving. The P0171 and P0174 were cleared as I got a new gas cap.

I do expect to have to change the canister and purge valve... I hear they are a common issue.

 

I got the same thing on my 2009 Sierra, same codes and fuel cap message. It was the fuel tank pressure selanoid and hose that I had to replace. It effects the pressure in the fuel tank and results inbad fuel mileage.

 

I got the same thing on my 2009 Sierra, same codes and fuel cap message. It was the fuel tank pressure selanoid and hose that I had to replace. It effects the pressure in the fuel tank and results inbad fuel mileage.

whereis it located and... do I need to drop the tank? that make sense why im haveing hard starts only after just filling up. this is a recent phenomenon.

 

"P0449 Code, 2008 GMC Sierra 5.3" go to that forum topic. The person replaces theirs and the codes clear.

 

My 2009 started with a p0496 & p0442 code so I replaced the canister purge solenoid. A week or so later it gave me a p0455 & "tighten gas cap" message and began to start rough immediately after refueling. After one particularly rough refueling episode I got a p0171 & p0174. I have checked the new canister purge solenoid it does fully close. I have also tried a new gas cap and new evap canister vent solenoid. Anyone have any ideas on what to check next?

 

Did you replace the hoses for it?

 

I had the same problem, and 496 keeps popping up. The rough idle still exists especially when under 45 degrees F at first start. Part of the issue was a loose spark plug wire. I fixed my purge vacuum issue (lines) but STILL hear a leak. I have a fog machine coming to smoke it out. Im thinking its either a bad seal on intake or valve cover (which dealer replaced 3 months ago when I showed them an AFM bulletin from the Forum).