# b&b,need your expertise



## wirenut (Jan 16, 2004)

my 04 1500 z71 failed inspection on a p0442 code..small evap leak 
where di i start...?

thanks


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## GSORK (Dec 6, 2003)

A lot of time its a bad fuel cap or a loose cap. Google the p code .


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## wirenut (Jan 16, 2004)

thanks will try


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## B&B (Nov 4, 2006)

Many are fixed with a simple fresh gas cap to replace the old one that's no longer creating a tight seal. Also get a few here and there where a few pin holes develop in the steel section of the filler tube or the clamps rust off so look over the filler assembly as well. If you get that far and still have the same issue go after the vent valve solenoid which is very common too as they'll stick partially open. Search "EVAP" as there's several decent threads on the subject here.


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## sweetk30 (Sep 3, 2006)

most are NOT gas caps any more these days. thats such a old mith. 

gm has problems with the location of the vent solinoid on them getting full of crap and leaking. there is even a recall on these. and the part is updated to move it to a better location.


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## RacingZR (Nov 14, 2009)

Not a GM but had the exact same code and error on my 03 Dodge and it was the fuel cap.


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## bill7101 (Nov 20, 2010)

At the shop i work at most of the ones i get with evap codes it is usually the vent valve that went to heck


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## cubicinches (Oct 19, 2008)

sweetk30;1174405 said:


> most are NOT gas caps any more these days. thats such a old mith.


You'd be surprised by how many are fixed with a gas cap or filler neck. Not necessarily GM trucks, but lotsa other makes. It's hardly a myth.


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## sweetk30 (Sep 3, 2006)

cubicinches;1174470 said:


> You'd be surprised by how many are fixed with a gas cap or filler neck. Not necessarily GM trucks, but lotsa other makes. It's hardly a myth.


might be but are you doin a full drive cycle to verify its fixed ? or does the cust say ah screw it and leave it on for a year and not tell ya. ?


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## 06Sierra (Nov 30, 2008)

Sorry to hijack your thread wirenut. Would a bad vent valve cause a gas smell? No SES light or stored codes. First noticed it late last winter, it went away over the summer and is now back. There are no leaks and the smell is coming from the filler area.


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## B&B (Nov 4, 2006)

sweetk30;1174713 said:


> might be but are you doin a full drive cycle to verify its fixed ? or does the cust say ah screw it and leave it on for a year and not tell ya. ?


Cube might but I don't because I don't let anything out the door unless I'm sure it's fixed. Change the cap, check the filler and pull 15 hg on the system for about an hour. If and only if it maintains then it goes out the door knowing it's fixed for sure. No need for a monitor drive cycle which is a potential waste of very valuable labor time anyway if you didn't get it the first time.

The quarter turn "click" caps are some of the worse at failing to properly seal. There's four different styles that fit about 80% of the common applications on the roads today and I always stock at least a couple of each just due to their common failure.


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## cubicinches (Oct 19, 2008)

B&B;1174926 said:


> pull 15 hg on the system for about an hour. If and only if it maintains then it goes out the door knowing it's fixed for sure. No need for a monitor drive cycle which is a potential waste of very valuable labor time anyway if you didn't get it the first time.


Exactly...

If you've got the equipment to find evap system leaks in the first place, then you'd be a fool to not test your repair, no matter what it was, before the vehicle leaves. Waiting for an evap monitor to run can waste a ton of time... _especially_ in the winter months.


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## stacks04 (Jan 22, 2008)

Yeah, most ARE gas caps with the lower percentage being small leaks elsewhere.


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## wirenut (Jan 16, 2004)

thanks all.
is the vent valve accessible on a 04 stepside or does the tank have to come out ?
also i heard you can use a unit from a cavalier which is the same and doesnt cost 200 bucks the stealer wants


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## B&B (Nov 4, 2006)

No need to pull the tank. It will be located either on the side of the left front bed mount bracket or on the rear of the tank just ahead of the rear axle.

Never tried a Cavalier valve but before they were available in the aftermarket for $40 thus had to be sourced from the dealer I used to use an '06 Suburban for an application for all the '04-newer trucks. Same valve as the actual application called for but cost $39 instead.


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## 2COR517 (Oct 23, 2008)

Half the CELs we see at work are EVAP codes. 80% of the time they just bought fuel, the cap is loose.


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## damian (Jan 29, 2009)

i wish most of my small evap leaks were gas caps. better get out the smoke machine with flow meter,and the scan tool to make the purge and vent valves close.


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## sweetk30 (Sep 3, 2006)

damian;1176737 said:


> i wish most of my small evap leaks were gas caps. better get out the smoke machine with flow meter,and the scan tool to make the purge and vent valves close.


that was our shop i worked at my self . not many caps . was valves / screwed up lines / rotted out fuel filler necks.


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## fordmstng66 (Dec 27, 2005)

sweetk30;1174405 said:


> most are NOT gas caps any more these days. thats such a old mith.
> 
> gm has problems with the location of the vent solinoid on them getting full of crap and leaking. there is even a recall on these. and the part is updated to move it to a better location.


My buddy Is a mechanic, and he ran into te same problem with the vent solenoid. Like you said the gm sells an updated kit to fix the problem.


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## wirenut (Jan 16, 2004)

thanks for all the help,
i pulled the can from the side of the tank blew it out and put 12v to it and heard it working so i put it back will see what happens also flipped the rubber seal on cap over. now is that box i took the hose off the charcoal can ? would that be a possible prob ? also where is this other valve on the engine located and whats it look like? will that give the p0442 code ?... sorry for all the ?'s


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## B&B (Nov 4, 2006)

Yes the "box" is the charcoal canister and it's a good idea to clean it out with a little compressed air once in a while especially if run in dusty conditions often.

A P0442 isn't normally caused by the purge solenoid valve unless it or it's tube or base O-ring has been physically damaged, say from someone working under the hood since it's mounted on the intake. Instead, your on the right track with cleaning the vent valve and canister except about being cheap and just flipping the gas cap seal over.


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## wirenut (Jan 16, 2004)

yea i am a cheap *******... can it be blown out while in place as it dont look like its gonna come out easily, rusted bolts
what actually goes wrong with the cap ? i've read that a lot of caps get replaced for nothing
also i shook the vent canister and heard a rattle figured it was a check valve , is it still good as the valve does work 
i pulled purge valve and that works..filler hose connection looks good,hoses look good 
still got cel though how long does it take to reset ?

thanks


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## sweetk30 (Sep 3, 2006)

fyi evap system is a o psi system basicly. and when testing it you pull a vacum on it. 

so if anyone is thinking of blowing out the system with compressed air YOU best know what your doing or you WILL trash the whole thing. and you wont want to know the price to fix that.


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## B&B (Nov 4, 2006)

wirenut;1179474 said:



> can it be blown out while in place as it dont look like its gonna come out easily, rusted bolts


 No need to remove it, disconnect the hoses and _gently_ blow it out with a little air. You'll likely find a some dust.



wirenut;1179474 said:


> what actually goes wrong with the cap? i've read that a lot of caps get replaced for nothing


The internal check valves fail, they're basically just a flapper valve deal. Dirt and age are the causes for it not to seal when the system is pulled to vacuum thus it can't hold vacuum for the required test cycle.



wirenut;1179474 said:


> still got cel though how long does it take to reset?


Did you clear the code? If not it can take multiple full drive cycles after the problem is repaired for the code to clear itself. If you did clear it and it came back then it's not fixed.


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## wirenut (Jan 16, 2004)

will disconnecting bat clear it ? cause its still there. only driven 10 miles or so

thanks


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## sweetk30 (Sep 3, 2006)

1996-up pull batt will turn out light. 

but will NOT clear the code. unless dead batt for few days.
computer has little internal batt inside. 

need a scanner to clear the codes.


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## wirenut (Jan 16, 2004)

thanks all for the insite....


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## 06Sierra (Nov 30, 2008)

I am getting ready to order AC Delco p/n 214-2149 for my 06 Sierra, P0449 code, and my 04 Yukon, gas smell when it's cold out. $17 each at rockauto.com. That is the p/n for the Yukon. Thanks for the tip on the trucks B&B. I was being too cheap to spend upwards of $100 for the solenoid for the truck!


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