Tighten Gas Cap message

[oldchev]

My 2004 Yukon Denali (w/6.0) has the tighten gas cap message irregularly. I bought used and was OK for 4 months them the MIL light came on. I have a scanner and the P0455 code registered.

The gas cap was not original so bought the NAPA Stand cap and put it on. Not the fix. I then used silicon spray on the first cap to allow smoother seating and made sure tight, was trouble free for a couple days then P0455 set again.I used the scanner to erase the code and I retightened it and was good for a couple days then the tighten gas cap message appeared. No code.

 

So I relented and bought the correct AC Delco cap. Same message. I then took off he vent valve solenoid assembly from evap tank and cleaned the filter and dust
from it and check the solenoid for function w/12 volts. happily I reinstalled it and it just told me to “tighten gas cap”. Hoses and lines looked good at the evap canister etc. and fuel tank fill lines.

 

Next: ??? Maybe the purge valve solenoid up front? Have a smoke test? Funny it set the codes real fast at first, then just the message.

 

[foghorn23]

Don't mean to hijack the thread, but this is sort of related. When did GM change the style of their gas cap on these trucks? My 2011 had the traditional cap that when turned to tighten would click, click, click, click, etc. On this new '13 when I turn it get one click and that's it. You could continue to turn, but no more clicks. I'm sure it's right for this truck, but in a world of un-tightened gas caps just one click kind of leaves me wanting more.....seems insufficient even though I know it's right.

[jhm]

 

My 2004 Yukon Denali (w/6.0) has the tighten gas cap message irregularly. I bought used and was OK for 4 months them the MIL light came on. I have a scanner and the P0455 code registered.

The gas cap was not original so bought the NAPA Stand cap and put it on. Not the fix. I then used silicon spray on the first cap to allow smoother seating and made sure tight, was trouble free for a couple days then P0455 set again.I used the scanner to erase the code and I retightened it and was good for a couple days then the tighten gas cap message appeared. No code.

 

 

So I relented and bought the correct AC Delco cap. Same message. I then took off he vent valve solenoid assembly from evap tank and cleaned the filter and dust

from it and check the solenoid for function w/12 volts. happily I reinstalled it and it just told me to “tighten gas cap”. Hoses and lines looked good at the evap canister etc. and fuel tank fill lines.

 

 

Next: ??? Maybe the purge valve solenoid up front? Have a smoke test? Funny it set the codes real fast at first, then just the message.

 

 

 

 

my problem after 2 smoke tests, replacing 2 valves turned out to be rust holes in the filler nck. the rubber hose was covering them so the smoke did not get out.

[oldchev]

The 2004 Denali has now set the P0455 code again. I have read numerous blogs and forums relating to this and of course, they first point to the gas cap, which I am sure it is not. The purge valve, normally closed creates the vacuum for the test (besides drawing vapors into the intake) then closes (no power) for the test. The vent valve (in back) normally open (no power) closes to seal for the test when activated. I intend to test these valves on bench for function. Without dropping the tank, I can then only suspect a hose, or the pressure sensor. Next chance will pour over this again, do the tests on the solenoid valves, check all visable hoses. I may have to indulge making my own smoke tester and see how that goes. I know the factory techs probably have a shortcut or probable cause for this so wondering if anyone has this insight. I don't give up easily and am relentlessly a DIY guy. I have the manuals for this vehicle and I am using the Innova 3130c for code retrieval and erase. The $$$K scanner I do not have. Suggestions?

[oldchev]

I will end this post with my fix to this problem.

It was the canister vent valve located at the rear of the vehicle. I took the valve off and bench tested it with a vacuum source.

 

 

Drawing through the vent tube side (to gas tank) of the valve I engaged the solenoid a dozen or more times. First only clicking of the solenoid but was still able to draw a reduced
amount of air through when energized (the leak). After working it several times and some silicon spray the valve closed on energizing and sealed. I reinstalled the
valve and drove it about 6 miles and the MIL light went off.

 

 

As I mentioned earlier the valve was very dirty and dusty when first removed. I assumed a grain of dust prevented full movement of the solenoid valve to close.

 

 

P0455 large leak: although gas cap was the message (probably the most common) it was the valve that wouldn't seat.

I will replace the valve with a new one, they're cheap enough. -oldchev

[txab]

Thanks for letting us know what solved your issue.

[Snow White]

i had 3 cracks in my purge valve shown there, got a replacement (the cheap one without the relocation kit, it's the old suburban one) took off the valve and swapped it out, then got the light, had to replace the stupid hose shown.... used 1/2" hose didn't even need clamps it was so damn tight to get on..... still waiting after a month for the light to come back on, fingers crossed but my repair looks just like that.

[Bad Bowtie2]

I heard (on another forum) about another guy who also used the CHEEPER suburban purge valve & it worked....

[Toby One]

What do you do when you have replaced everything?  Thinking about replacing evap solenoid again. To see if got bad one.   Would love your thoughts. 

[davester]

smoke test the system and see where it's leaking.