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Thread: P0641 code

  1. #1
    Join Date
    Jun 2007
    Location
    Watkins, CO
    Posts
    73

    Default P0641 code

    2003 LB7. 127K miles. Saturday I noticed a slight irregular idle during a 4-5 minute idle. This morning when I started it for work, the check engine light stayed on, but it seemed to run normally. Same when I left work.

    Got home, shut it off and went into the garage to get my scan tool. Connected the tool and saw the P0641 (sensor reference voltage A circuit / open) code (key on engine off). Cleared the code and it immediately came back along with the "reduced power" message in the DIC. Tried starting and it would barely stay running. At this point I also saw a P0193, but it didn't store that code. Shut it off and went in the house to call a friend and do some research. Went out a little later and it started back up with just an occasional bounce in the idle.

    We watched on the scanner and could see the fuel pressure bounce wildly when the idle changed. My buddy (who works mostly on Ford diesels) seems to think it's the fuel pressure sensor failing.

    I just wanted to see what everyone here thinks before I buy a new FPS.

    Bob
    tufcj

  2. #2
    Join Date
    Apr 2001
    Location
    CA
    Posts
    13,573

    Arrow

    Change the fuel filter, first.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  3. #3
    Join Date
    Mar 2000
    Location
    Loyal WI US
    Posts
    10,792

    Default

    I'll add that the fuel pressure sensors seldom fail, but the regulators do.
    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
    Superflow Lie Detector in house
    2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
    2005 Chev K3500SRW D/A CC Long LT(SOLD)
    2007 Chev K2500 Classic EC Short LT (Sold)
    2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
    2016 GMC K3500SRW D/A CC short LTZ

    Custom tuning in house using EFI Live tuning software!

  4. #4
    Join Date
    Jun 2007
    Location
    Watkins, CO
    Posts
    73

    Default

    Fuel filter was replaced about 2000 miles ago, at the last oil change. Hasn't been a problem. I used a Luber-Finer fuel filter.

    Would the regulator cause a P0641? We watched the fuel pressure on the scanner vary at idle from 4700PSI to 18,000psi, the idle would bounce with the pressure changes.

    Thanks.

    Bob

  5. #5
    Join Date
    Mar 2000
    Location
    Loyal WI US
    Posts
    10,792

    Default

    if the idle is oscillating with the pressure changes there is a good chance that the pressure is actually doing what you are seeing and the regulator is getting flaky. I'd start with teh common failure regulator and see what happens from there.
    Kennedy Diesel-owner
    More than just a salesman-I use and test the products that I sell on a daily basis!
    Superflow Lie Detector in house
    2002 Chev K2500HD D/A CC Long LT 11.77@ 124mph at 7700# fuel only-e.t. needs help
    2005 Chev K3500SRW D/A CC Long LT(SOLD)
    2007 Chev K2500 Classic EC Short LT (Sold)
    2012 GMC K3500SRW D/A CC Long LTZ Happy Birthday to me! Built 1 working day after my birthday and delivered 7 days later.
    2016 GMC K3500SRW D/A CC short LTZ

    Custom tuning in house using EFI Live tuning software!

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