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Gary
Gary, Chevy Technician
Category: Chevy
Satisfied Customers: 16893
Experience:  15 years GM master tech
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My 2004 Chevy suburban awd 1500 5.3l flex randomly tells me

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My 2004 Chevy suburban awd 1500 5.3l flex randomly tells me on the DIC on the cluster that I need to tighten the gas cap. I replaced the cap with gm part and still does it. It is plenty tight. I also get a low voltage code for knock sensor several new emissions parts replaced recently too.

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Customer: replied 10 months ago.
No drivability issues with or without the message.

with a new gas cap and it still does that there has to be an intermittent fail of when the computer tests the fuel system and when it fails it thinks the gas cap is loose

a shop will need to perform a smoke test on the evap system and see if the vent solenoid it bad or not closing or if there is a small leak on the system as they will visually see smoke leaking

as for the knock sensor these are very common for both knock sensors bad and the small wiring harness to them causing that issue

any shop can change them for you and they should see the bulletin on the knock sensor replacement

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Customer: replied 10 months ago.
I have a fog machine from Halloween can that be used to push smoke for a test?
Customer: replied 10 months ago.
I am a very good shade tree mechanic but the emissions is a pain
Customer: replied 10 months ago.
I have seen the 0440 code for emissions a few times

no a scan tool is needed to close the vent solenoid to do the test

99 % of these with a new gas cap setting this code ends up being a bad vent solenoid

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Customer: replied 10 months ago.
the vent solenoid is closed with vehicle off. Fill tank with smoke and look for leak. Likely the vent solenoid?

the vent solenoid is only closed when the computer tells it to close that is why you need the scan tool to close it

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Customer: replied 10 months ago.
I have replaced it but it was an inexpensive aftermarket part.

that is why it needs to be smoke tested with a scan tool closing the solenoid to visually look for the leak or smoke

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