PO455?

changed out the gas cap and i still get the CEL with this code. replaced with Ac Delco original part. what should i look at next? i dont see any gas leaks anywhere but i do smell gasoline in the air sometimes around the truck on start up.

Leak in Evap system check ALL hoses, connections and solenoid(s)/Charcoal canister for leaks, cracks, holes, etc.

Maybe the purge valve. I believe it’s located on the charcoal canister in front of the fuel tank. It’s a cheap to try and easy to swap out. P0455 just means a large vapor leak is detected, the PV is high on the list of probabilities.

what year is it? on my old 2000 there was a air injector pump in the engine compartment left side passenger corner pocket where they moved the battery to on the 2007+ mine had a leak and I believe it was the same code, found one in the junk yard, swapped it and code went away, the air injector would inject air into the engine for the first minute or so to help at startup but they eliminated it a couple years later

Doubeleive said:

what year is it? on my old 2000 there was a air injector pump in the engine compartment left side passenger corner pocket where they moved the battery to on the 2007+ mine had a leak and I believe it was the same code, found one in the junk yard, swapped it and code went away, the air injector would inject air into the engine for the first minute or so to help at startup but they eliminated it a couple years later

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its a 2004. gonna work on this issue after i finish the 100k maintenance today.

This is specifically for the GMT900s but yours should be similar or the same. No other codes? This P0455 is a LARGE leak code.

 Inspect for a loose, missing, damaged, or incorrect fuel fill cap.
 Inspect for a damaged fuel filler neck seal surface.
 A blockage or restriction in the EVAP purge solenoid valve, purge pipe, EVAP canister, or vapor pipe,
can cause this DTC to set.
 The EVAP system can be filled with smoke more quickly and completely by opening the system opposite
the end where the smoke is injected. For example, when injecting smoke at the service port remove the
fuel fill cap, or temporarily leave the vent open, until smoke is observed, then close the system and
continue testing. If using a fuel cap adapter at the filler neck, use the J 41413-VLV at the service port to
allow the system to fill faster. See Special Tools .
 To help locate intermittent leaks using the J 41413-200 , move all EVAP components while observing
smoke with the J 41413-SPT . See Special Tools .
 Individual components can be isolated and tested using adapters in the J 41413-300 .
 A condition may exist where a leak in the EVAP system only exists under a vacuum condition. This type
of leak may be detected by using the scan tool Purge/Seal function to create a vacuum in the EVAP
system and then observe the FTP parameter for vacuum decay.

can someone give me the parts numbers for these pieces so i can order them?

2004 chevy tahoe 5.3l v8 LT

I had the same code on mine and it drove me nuts to try and fix it. The Diagnostic Tree is readily the same as the one posted above by Swathdiver, however, the funny thing is the diagnostic tree makes it sound like you have a big hole in your hoses or valves when in fact its still a tiny hole. I think Car companies came up with the change gas cap direction as a way to sell product lol. Unless you are trying to pass state emissions or are very particular about your vehicle (nothing wrong with that) the best and cheapest thing to do is to clear the code and drive it. It will come back in about 10 days and then clear it again. If you perform some of those tests, you will need a bi scan tool and some other special tools. Because those hoses are plastic and some are not easy to reach, you could have a hell of a time doing this. When you start having problems filling the tank, then you will have to do some of those tests. Good luck with it

What you need is someone with a tech 2 or equivalent (not just a plain scan tool) to check the evap system. There is a guy (Eric) up in NY that owns his own shop and does alot of vids for even our C/K chassis GM's. Check this video out of his for knowledge of the Evap system and how to troubleshoot it.

Here is a video that goes into the P0455 code and a typical failure cause.

UrbanSuburban said:

I had the same code on mine and it drove me nuts to try and fix it. The Diagnostic Tree is readily the same as the one posted above by Swathdiver, however, the funny thing is the diagnostic tree makes it sound like you have a big hole in your hoses or valves when in fact its still a tiny hole. I think Car companies came up with the change gas cap direction as a way to sell product lol. Unless you are trying to pass state emissions or are very particular about your vehicle (nothing wrong with that) the best and cheapest thing to do is to clear the code and drive it. It will come back in about 10 days and then clear it again. If you perform some of those tests, you will need a bi scan tool and some other special tools. Because those hoses are plastic and some are not easy to reach, you could have a hell of a time doing this. When you start having problems filling the tank, then you will have to do some of those tests. Good luck with it

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that little cel light drives me nuts. im actually working through a list and this is last on the stuff to keep the truck maintained before i start again with fun stuff. no problems filling the tank...just a gas smell from the rear and the cel light. if i clear it it comes back on same day actually. maybe the next day. never much time before its back, im willing to change out the peices i can before checking all the hoses and smoke tests if i can get some part numbers.