2005 Avalanche P0455

I've read on a few of these threads on here regarding this code.  Mine didn't come up until I replaced the evap canister vent valve solenoid due to having the gas tank fill up issue where it would cut off early.  When I disconnected the hoses to the vent valve solenoid and the evap canister, small pieces of charcoal fell out of the evap canister so I went ahead and replaced it as well.  Soon after, the P0455 code popped up and the warning to tighten my fuel cap came on.  I double checked everything to make sure it was connected properly and don't see anything wrong.  I cleared the code hoping it was a fluke but it came back.  I bought a new Stant gas cap and cleared the code and it came back again.  I've checked the vent valve solenoid and it opens and closes as it should along with the purge solenoid on the engine.  I've checked the fuel lines from the tank to the fuel filler and they appear to be fine as well.

I'm not sure what else to check but I'm tired of seeing this keep coming up and the CEL coming on because of it.

Any suggestions?

Will be keeping an eye on this one , still tacking down my p0455 in my 05 2500

Update: I cleared the code and it stayed off over a week until yesterday. Being that it stayed off for a bit, could it be the fuel pressure sensor on the tank? Is there a way to test that?

One way is a smoke test, I think $100 is what it cost . Just looking for an air leak.

Weezul said:

Update: I cleared the code and it stayed off over a week until yesterday. Being that it stayed off for a bit, could it be the fuel pressure sensor on the tank? Is there a way to test that?

Click to expand...

  https://www.youtube.com/watch?v=Xc4UJIU0M70

Check out their web site.

Had a smoke test done today and there aren?t any leaks. It completely seals up. Any ideas why it keeps throwing the code and telling me to tighten the gas cap?

I'm guessing you have a leak at one of the hoses attaching to the evap cannister after installing the new one.  You have a leak somewhere.

After driving this a little while I?ve noticed a pattern. When the truck is cold it will tell me to tighten the gas cap. Once the truck is warm it won?t do it the rest of the day. Also, if it?s really hot out (90+ degrees) in the morning it won?t do it. Makes me think where ever the leak is is in a hose that expands when it gets hot and closes the leak until it cools back down.

It?s frustrating for sure.

Do you have something that can read the Fuel tank Pressure Sensor?

Personally no but when they did smoke test he said the purge valve and vent valve were working. Not sure if he tested the fuel tank pressure sensor.

If you have an inspection camera or maybe a mirror set just right so you can see the top of the gas tank. look for rust on the fuel pump.  Maybe the fuel pump seal is leaking or the sensor is bad.

https://www.youtube.com/watch?v=W-OuwkNG1rI

Nowadays the mechanics have to have the equipment that can read the sensors.