GM's Elusive codes P0440, P0455 and P0442

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  • Bob's Garage
    Senior Member
    • Nov 2007
    • 3257

    GM's Elusive codes P0440, P0455 and P0442

    I have an idea for a good Troubleshooter tip unless it is already used.

    It dawned on me the other day, that we have done a lot of fuel filler necks on GM products for P0440 General Evap Problem & P0455 Evap Large Leaks and possible P0442 small leaks.


    98 Olds Intrigue:

    1998 INTRIGUE Fuel filler neck 2 002.jpg


    The first one I did several years ago kicked my a$$, until I smoked the evap system from the gas cap surface on the filler neck forward. That is when I found the fuel filler neck leaking.

    There is a check valve in the fuel tank that blocks pressurized smoke from getting to the filler neck. A normal smoke test from the purge hose will not reveal this problem. The normal conclusion is that there is no leak.

    The PCM knows that there is a leak because it uses vacuum to find Evap leaks and vacuum actually pulls the check valve away from it's seat whereas pressurized smoke tends to isolate the filler neck leak by holding the check valve closed.

    Another effect of smoking the evap system with pressure is it tends to seal the vent valve solenoid tightly and it cannot release when commanded due to pressure holding it closed after the initial bi-directional command to close it for smoke testing. This can cause a false alarm causing some to believe the vent valve is defective. The Vent valve then opens and closes normally when pressure is released.



    This is a huge problem in the "rust belt" where salt causes filler neck corrosion around a plastic "no spark" filler hole. Eventually, the plastic loses its bond with the metal filler neck causing a small, to large evap leak.

    1998 INTRIGUE Fuel filler neck 001.jpg

    I have seen this on GM vehicles from the late 1990's to the early 2000's (with more on the way, I suspect) such as Grand Ams, Malibus, Grand Prixs and Impalas

    Some filler necks are already obsoleted by GM but aftermarket replacements are available through Dorman and Spectra, but the last Dorman one we did was a poor fit though... It literally forced me to stretch the filler hose to it's limit.



    Thanks, Bob
  • greasybob
    Senior Member
    • May 2008
    • 1590

    #2
    Does Snap On have an upper midwest division for it's trouble shooter writing team so it can include the common rust related failures we see around here but probably never seen in sunny California.

    Comment

    • Bob's Garage
      Senior Member
      • Nov 2007
      • 3257

      #3
      Rust, a way of life in the upper midwest...

      Ya, ey dere Bob,

      I like that- "Troubleshooter Upper Midwest Edition" or "Rust Belt Division".

      One thing I would like to see Bob, is "Rust times" for labor operations on different repairs. We know what's involved there, eh Bob?

      What part of Wisconsin are you in Bob?

      Bob
      Last edited by Bob's Garage; 03-19-2013, 04:12 PM.

      Comment

      • Joe Rappa
        Snap-on DSD
        • Aug 2007
        • 2050

        #4
        I agree that the EVAP Code section could use some additional attention. This is a great start. One thing that has always bugged my about the EVAP TS stuff is that it mentions that Techs report lots of bad gas caps. I strongly disagree with that. Gas caps certainly do fail, but it's never high on my list of usual suspects. I'd like to see that part removed.

        Joe
        "You don't build a reputation on what you're going to do"
        Henry Ford

        Comment

        • Orevin
          Senior Member
          • Aug 2010
          • 1110

          #5
          Originally posted by Joe Rappa
          I agree that the EVAP Code section could use some additional attention. This is a great start. One thing that has always bugged my about the EVAP TS stuff is that it mentions that Techs report lots of bad gas caps. I strongly disagree with that. Gas caps certainly do fail, but it's never high on my list of usual suspects. I'd like to see that part removed.

          Joe
          Joe,

          I agree with that. On the other hand... Most gas caps have already been replaced before the car comes to a shop... It has a high failure rate at the big parts stores, just like EGR valves
          -Kai-
          Chicago, IL

          Comment

          • greasybob
            Senior Member
            • May 2008
            • 1590

            #6
            Center of the state. Always do your leak checking and smoking from both ends. If the tank is over half full on some models ther smoke will never make it up to the filler neck or cap.

            Comment

            • Trindaddy
              Senior Member
              • Jan 2010
              • 339

              #7
              Hey Greasy, I have come across this on gMs too. Now, during any evap leak test I ALWAYS undo the cap after i've looked at it for leaks to see if psi drops and smoke emits on all cars. Then test from neck if needed.
              I also took a Napa gm cap, removed the inner trim plastic piece then trimmed away the plastic from the outer diameter, drilled hole in top, and put a piece of fuel line in the hole. You will see that it fits nicely in the inner bore of the cap vent. Just put a little RTV to seal and keep it. Now when you use it and smoke does emit from this area you will easily be able to see whether it is the cap seal or where the metal neck meets the plastic liner of the neck. By the way, I have found that every GM that this happens with fits this one cap/rig i made. New Englanders also have a very special relationship with fasteners and the matching skillset to remove them.

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