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Old 04-07-2013, 09:14 PM   #1
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Default evap problems

Hi all. I have a 2009 Silverado with 80,000 loving miles on it - all original save for the automatic fluid and filter (changed at 50,000 miles per friend'* recommendation) and routine oil and filter changes. 2 weeks ago the check engine light came on and OnStar had me check fuel cap tightness then continue to drive for 7 starts to see if light would go off. It did not, so I had a local dealership perform a diagnostics scope scan which displayed codes P0455, P0440 and P0496. Traced circuits showed vehicle needs fuel tank pressure sensor and EVAP vent valve. I live in rural Oregon and we have no required emissions checks. My problem is that the dealership quoted me over a $1000 for the replacement of these parts. An independent repair shop said that the codes only point to a defective tank pressure sensor and that he can replace it for under $280. My question, is the independent mechanic correct in his deduction
or should I also replace the EVAP vent valve as well? I have not noticed any change in the idle or acceleration of the truck or gas kickback during fueling. Appreciate any opinions or ideas.
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Old 04-07-2013, 09:27 PM   #2
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welcome to the site im going to move the post to the chevy technical section

as far as the truck evap codes whenever one comes up i would suspect the vent valve 75% of the time, you can check it take it off the truck and blow through it. if you put 12v on it and it closes and you cant blow through anymore its fine. the pressure sensor is hard to check and on most vehicles on top of the gas tank. so alot of the charge is in labor im sure.
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Old 04-07-2013, 11:58 PM   #3
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Default Thanks Justin

As I understand it, the vent valve (solenoid) on the Silverado is located above the spare tire and easily reached - without having to drop the fuel tank as is required to reach the pressure sensor. I further understand that there is a much cheaper replacement part than the original from GM that works just as well, but am unsure of who manufactures it. Should I replace the solenoid and not the sensor and have the check engine light cleared and see is that resolves the problem?
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Old 04-08-2013, 07:41 AM   #4
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im saying you should test the vent. if its fine, the last thing is the pressure sensor. if its not fine doesnt seal every time if you activate it with a battery then replace it and clear the codes and see if any come back.

you can get delco or delphi parts, from rock auto, advance auto, sometimes amazon. rockauto has it under emmision/ canister purge valve. it not the purge valve though.

ACDELCO Part # 2142082 SOLENOID KIT,Evaporative Emission Canister VENT SOL VLV
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Old 04-14-2013, 05:03 PM   #5
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Default Thanks again, Justin

"as far as the truck evap codes whenever one comes up i would suspect the vent valve 75% of the time, you can check it take it off the truck and blow through it. if you put 12v on it and it closes and you cant blow through anymore its fine"

I did as you described and the valve remained open with 12v charge - no clicking sound to indicate a valve closure and I could still blow through it.
So, I went online to Amazon and ordered the rebuild kit for half of what the local parts store wanted.

Will let you know how it turns out. Thanks again for your help. Howard
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Old 04-14-2013, 05:30 PM   #6
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Howard,

I also am having P0040 problems on my GM vehicle (Bonneville). I have done many repairs, but never seemed to understand the fuel/emissions issues.

What I have come to learn is there is essentially one "pipe" from the gas tank filler (gas cap) to the air intake. During the length of the pipe there are vents and other things, like the gas tank, vapor canister purge valve, vapor canister vent solenoid, and a vapor canister filter . Along this pipe there is a tube that connects all of these.

Think of this pipe as being plumbing as going from the outside water source (gas tank) to the bathtub (air intake). Along the way there is a water filter, toilet and sink. Any of these develop a leak and cause a reduction in water pressure. No different with our fuel evap system. Anywhere there is a leak or blockage from the gas tank to the air inlet may cause a error code to pop up. By following the pipe from end to end- you can get a good feel of where the problems may be popping up.
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Old 04-14-2013, 05:41 PM   #7
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Me personally i would change the evap vent valve. Then clear the light and see if the codes come back for the pressure sensor.
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Old 04-14-2013, 10:55 PM   #8
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I am a Ford tech, but all these car companies use the same vendors for their parts, and their engineers are always jumping from company to company so problem usually transcend across car lines. Whenever you buy a car anymore, you are not buying a GM or a Ford, but you are buying a GM/Ford/Dodge/Asian/European cross breed. And they are all built in Mexico. Well....except the Asian cars. (Buy Japanese, put Americans to work; buy American, put Mexicans to work) Anyway...
I would bet that the dealership tech is shot gunning the problem for fear of a recheck because these dealerships are **** camps run by satanic service managers who just about have you drug out back and whipped for getting a recheck once every five years or so. That is one big reason why all the best techs are leaving the dealerships to start their own shops or go to a good independent (I.E., NOT Goodyear or Firestone)
If it was me, I would say take a look underneath the rear of the truck. Dirt and debris likes to get up in the vent hose, especially if you are on dirt roads a lot. Also mud dobbers and other bugs build nests in there, I guess they like to get high on the gas fumes.
These FTP sensors do fail sometimes, but they are just about bullet proof, so not in most cases.
I would bet you have one of three possible problems. 1) the EVAP vent solenoid has sucked some dirt into it due to the suction whenever it vents. 2) You could have an intermittently sticking EVAP management valve, 3) you really do have an intermittent EVAP leak, which can be temperature sensitive.
There is still the outside possibility of an FTP sensor, but not likely.
Whatever you do, likely it will be somewhat of a guess, so by all means do it as cheaply as possible because you may be revisiting the issue at some point.
Don't worry about aftermarket parts. All these parts are made by the same 12 year olds in India for $2 a day and a lot of aftermarket parts are just reboxed OEM parts anyway.
It seems like the EVAP vent valve is the best place to start, especially if you see a bunch of dirt or mud up around the vent hose area. You might get lucky, with EVAP issues, it can be a big crapshoot especially if the issue is intermittent.
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Old 04-22-2013, 08:51 PM   #9
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Default Problem solved

I replaced the vent valve as you all recommended and reset the error codes.
Check engine light has not relit. I thank you one and all for your guidance.
Great forum you have here.
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Old 04-23-2013, 07:33 AM   #10
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thanks for updating the fix
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