Looking for assistance from those who have intimate knowledge of this issue and corrective action.

I have a 2012 GMC Sierra SLE Z71 5.3 flex fuel that recently threw a P0455 code. Did some research and checked the fuel tank vapor vent. I thought the solenoid should actuate (click) every time the key was turned on and mine didn't. I changed the vapor vent solenoid and cleared the code then drove the truck for dang near 100 miles (as suggested by a friend). Code remained. I read somewhere that the vapor vent solenoid will only actuate when certain conditions are met and it is commanded by the PCU. I found that the 2nd most common problem with the vapor vent solenoid is faulty wiring - so I replaced the wire connector at the solenoid. No change. I must have cleared (erased) the code at least 2 X's with my hand held reader at this point and was now getting a "permanent" P0455. So I stabbed the problem by replacing the purge solenoid in the engine bay. Took it for a test drive and discovered that the code was now pending versus permanent. At some point I then found two P0455 codes; one pending and one permanent. I dug into the permanent code issue and found specific "driving cycle procedures" from GM. I did their procedures several times and still throws a permanent P0455.

I order a new gas cap for $8.00 and that should be here tomorrow, Monday July 27th.

I'm looking for some pointers from people who have solid experience here. I am not a "change parts to find the problem" kind of guy. I don't have a repair manual and prefer not to pay $90 or more an hour for the shop to look it over. I did a thorough inspection and cannot see anything obvious and only replaced the fuel tank vapor vent solenoid because that seemed to be the #1 culprit after a gas cap. The I replaced the purge valve & solenoid. I will try a new gas cap tomorrow since I already bought it. It seems that a smoke test to find the leak is the best option. It could also be that the aftermarket vapor vent solenoid went bad - or was not quality to begin with (it was a Dorman product).

Thanks in advance and I look forward to some first-hand mechanical experience for you!

ChiefH

 

I narrowed the culprit down to the fuel pressure sensor which is located in top of the fuel tank near the pump/sender assembly. I searched YouTube and came across South Main auto. He took in a vehicle that another shop couldn’t fix the problem even after replacing the fuel tank vapor vent solenoid and the purge solenoid.

The fuel tank pressure sensor did not throw a code but during his troubleshooting (using a $5000 scan tool) he found an issue with the sensor.

Like him I did not drop the tank. Luke him the sensor nipple that slides into the tank broke off. I could not pull it out so I pushed it into the tank. I then used my automotive picks to pry out the aqua green / turquoise blue seal. The seal comes attached to the new sensor.

i tried to lube it with assembly lube and then engine oil to get the sensor pushed back into the port on top of the tank. Nothing doing. Then I pulled out the KY jelly I keep on hand for carb gaskets and such and that worked.

to get the sensor in you need to push down AND rotate to “twist” it down in. There is limited room to turn & push and your arm is already contorted. Be patient and you’ll get it. I was not about to drop the tank or lift the bed.

in NYS they dump tons of corrosive slurry or salt on the roads and that stuff will eat anything it comes in contact with. I knew if I tried to raise the bed or drop the tank that I would create more problems so I just blew the top of the tank off with compressed air - especially around the pump / sender assembly and got to work.

A new sender for my truck costs about $56. That and the cost of the vent and purge solenoids were much cheaper than paying $90 an hour to a shop.

I was in the verge of making a smoke “leak detector” to visibly see if one of the lines or connections were compromised. You can find DIY vids on YouTube for that.

Hope this helps someone.