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Thread: P040B/P041B, EGR circuit

  1. #1
    Join Date
    Jan 2006
    South Milwaukee, WI

    Default P040B/P041B, EGR circuit

    2017 L5P: I've gotten a couple of P040B and P041B (EGR Temp circuit "A" and circuit "B"sensors). No CEL has been set; but the Warm ups w/o Emissions Malfunction counter is reset to "0". I'm having difficulty determining exactly where these sensors are located. I'm making the assumption that these are 2 distinctly located sensors. Since the information I'm seeing on the web doesn't specifically state they are related to the EGR Cooler, I'm thinking somewhere in the exhaust stream before and after the EGR valve itself.

    I'm seeing one sensor that is located between the EGR valve and the intake (after the throttle body) and I believe there is another on the right side (passenger side) manifold (before the "up pipe" to the EGR valve). Am i close in my assumptions and if so, which one is "A" and which is "B"? Or, am I all wrong to begin with?

    Any advice is always appreciated. Thanks!
    So. Milwaukee, WI
    '01 2500HD, LB7, ~440K miles
    "Stock" engine. Dual fuel filtration system with Kennedy lift pump, BF Goodrich Commercial T/A Traction tires (sold to a dude from Texas- it's living a warmer life just fine down there now!).

    '17 2500HD, L5P (Happy Birthday/Merry Christmas to me!!!) Currently bone stock, 120K miles.

    "Socialism is a philosophy of failure, the creed of ignorance and
    the gospel of envy. Its inherent virtue is the equal sharing of misery."
    Winston Churchill

  2. #2
    Join Date
    Apr 2001


    Sensor ID is simple. Unplug one before a cold start. Repeat with the other before it warms up. The computer will complain appropriately. Logically, "EGR Temp circuits" would certainly be before, and after the EGR and/or cooler. Other than that, you're probably guessing in the right direction.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A

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