2002 Buick Lesabre P0440

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  • 19mopar
    Member
    • Oct 2010
    • 38

    2002 Buick Lesabre P0440

    Vehicle has code for general evap failure. Smoke test system from service port and from fuel cap, no leaks present according to flow meter on smoke machine. While smoke testing under pressure the FTP pid reads 6.34 mmHg converted to 3.39 "H2O and FTPV is .8v. When command purge at 50% and vent valve closed, pids read: FTP -5.98mmHg converted to -3.19 "H2O and FTPV is 2.2v. When sealing system and commanding purge to 50% i am reading about 7"Hg at the service port, after vacuum guage smooths out. The FTP pid is kinda eratic sometimes and I think I should see higher pressure and vacuum values in my limited EVAP expierience (learning new things everyday on the EVAP info). I am kinda leaning on a faulty FTP sensor but am wondering if sensor can be removed and apply vacuum directly to sensor and monitor pid to verify sensor replacement. After doing alot of reading and trying to understand EVAP data from alldata i understand the PCM uses the FTP value to determin if a fault is present in EVAP system. Looking for info from some more experienced EVAP techs.

    Thanks a bunch
    Darren
  • Joe Rappa
    Snap-on DSD
    • Aug 2007
    • 2050

    #2
    Hi Darrenn,

    Fuel tank pressure sensors don't fail too often on GMs. Not that that can't be your problem, but the numbers you posted don't worry me. When pressurized with a smoke machine GMs read read around .4-.5V.

    A P0440 can be caused by a lot of things on a GM.
    Any chance you haven't cleared the code yet? If you didn't please post the PID Data for the purge valve, Vent Valve and Fuel Tank Pressure Sensor. We may get a hint there.

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

    Comment

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

      #3
      Deja Vu


      Strange, I have a 2002 Le Sabre in my shop now with a P0440. My testing shows similar results to Darren's. I smoked mine from the gas cap surface (preferred) and it holds pressure well.

      That could be the issue here. We use pressure to check the system. The PCM uses vacuum. Pressure can seal leaks in small cracks in hoses etc... The filler neck on this vehicle is not steel, like the ones that rust badly and leak.

      This morning I will perform the Evap Service Bay Test. I did not try that yesterday, the engine was too warm.
      This may show a leak...

      Joe, I respectfully disagree with you. I have seen a fair amount of FTP Sensor failures in my area. After all, what doesn't fail on a GM fuel pump module?

      The FTP sensor diagnosis is fairly simple. I like voltage as a static indicator of health. The spec I use is KOEO , GAS CAP OFF 1.3-1.7 Volts.

      If not, I cheat a little. Since there is little space between the FTP sensor and floorpans of cars you have to drop the tank for testing. I may have to lower the tank slightly. I have several known good FTP sensors, removed from GM fuel pump modules prior to throwing them away. I use one to to quickly test electrical integrity of the FTP Sensor circuit. i simply reach above the tank , if I can't, I lower the tank and unplug the FTP sensor and plug in the new one, check my values on the scanner.

      This is not my preferred way of diagnosis, but I can then sell my repairs, wiring or sensor or both. If I can't sell either, I haven't had to pull the tank out.

      Back to the LeSabre, I will post my findings today.



      Thanks, Bob

      Comment

      • 19mopar
        Member
        • Oct 2010
        • 38

        #4
        Bob I think on these lesabre's there is an acess panel in trunk area to get at FTP sensor. I had an opening of an hour yesterday to squeeze this customer in but he needed car back at the end of the day so i wasn't able to confirm the access panel. Will get vehicle back after the holiday.

        Comment

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

          #5
          Originally posted by Bob's Garage

          Joe, I respectfully disagree with you. I have seen a fair amount of FTP Sensor failures in my area. After all, what doesn't fail on a GM fuel pump module?

          The FTP sensor diagnosis is fairly simple. I like voltage as a static indicator of health. The spec I use is KOEO , GAS CAP OFF 1.3-1.7 Volts.




          Thanks, Bob

          Not to worry Bob. That's what these forums are for. When it comes to fixing cars we all rely on our own experiences. I recall finding only 2 bad fuel tank pressure sensors on GM vehicles that caused EVAP Codes. One would only register 1.4V regardless of the actual pressure/vacuum in the tank. The other read 0V all the time.

          For a while I also remember a bunch of FTP Sensors on Trailblazers shorting the 5V reference to ground. It would cause stalls and no starts and a laundry list of codes related to a low 5V reference, but they never came on for EVAP problems.

          What are you finding with the ones you find faulty? Is there a pattern failure? Of course no sooner do you say this than I will run into one, right?

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

          Comment

          • 19mopar
            Member
            • Oct 2010
            • 38

            #6
            I have Freeze frame data from running a failed EVAP service bay test but there is no pid shown for the FTP. I also don't know how to attatch a file from my Shopstream Connect to this forum. If any one could help walk me through it I could post. Thanks.

            I think I figured how to upload attatchment. If it doesn't work let me know, thanks.

            Darren
            Last edited by 19mopar; 07-30-2011, 04:09 PM.

            Comment

            • Crusty
              Senior Member
              • Dec 2007
              • 2450

              #7
              Originally posted by 19mopar
              I have Freeze frame data from running a failed EVAP service bay test but there is no pid shown for the FTP. I also don't know how to attatch a file from my Shopstream Connect to this forum. If any one could help walk me through it I could post. Thanks.

              I think I figured how to upload attatchment. If it doesn't work let me know, thanks.

              Darren
              Hmmmmm...."there is no pid shown for the FTP"
              Herein lays one of my concerns.....but I'm not supposed to say anything about missing pids or pids in inappropriate value scales.

              It uploaded fine....just no useable data in there.

              Comment

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

                #8
                Unfortunately when it comes to freeze frames, the scanner only displays what the cars stores. At least GM has a nice big freeze frame, instead of the short OBDII Data stream like everyone else. They sure give you a lot of data, including the failure records, so you can get pass/fail ratios for the codes.

                GMs of this vintage set P0440s when they close the vent valve, open the purge valve, and no vacuum develops in the system. You can see on the freeze frame that the car set the code at only 3.5 minutes of run time, and both the purge valve and vent valve are on. Unfortunately you can't confirm the FTP, but I don't think you don't need to in this case. It has a code for it.

                Hopefully you can keep trying the purge/seal test and reproduce it. If it's intermittent my first suspect would be a faulty vent valve, but I wouldn't hang one until I could confirm it.

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

                Comment

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