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Peterbilt 379 Cruise not working

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Akkaid, Dec 27, 2020.

Page 4 of 4
  1. Jan 5, 2021 #31
    TTNJ

    TTNJ Heavy Load Member

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    So that leads me to believe that the CC is not working because it is supposed to not be working......something like, oh I don’t know, maybe the brake foot valve is sticking.

    Whatever you discover please keep us posted. I love reading this stuff to educate myself
     
    TTNJ, Jan 5, 2021
    TTNJ, Jan 5, 2021
    #31
    Anderson1551 Thanks this.
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  3. Jan 5, 2021 #32
    pushbroom

    pushbroom Road Train Member

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    If the foot brake valve was sticking his brake lights would be stuck on as well as the brakes dragging.
    He can verify it is not by testing the brake switch which he has by checking it with a multimeter as well as reading the position with a laptop.
     
    pushbroom, Jan 5, 2021
    pushbroom, Jan 5, 2021
    #32
  4. Jan 5, 2021 #33
    pushbroom

    pushbroom Road Train Member

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    "If" you trust the tech with the laptop, it looks like you could have a ecm issue. That is a pretty big if.
    I did replace a cat ecm once for not entering cruise mode. Not saying that is your issue however.
     
    pushbroom, Jan 5, 2021
    pushbroom, Jan 5, 2021
    #33
  5. Jan 6, 2021 #34
    TTNJ

    TTNJ Heavy Load Member

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    Speaking from my experience the brake lights would not come on unless it was a “heavy” stick on the valve. There is basically a dead zone there
     
    TTNJ, Jan 6, 2021
    TTNJ, Jan 6, 2021
    #34
  7. Jan 6, 2021 #35
    Akkaid

    Akkaid Bobtail Member

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    Akkaid, Jan 6, 2021
    Akkaid, Jan 6, 2021
    #35
  8. Jan 6, 2021 #36
    Inderjit

    Inderjit Medium Load Member

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    Can you disconnect the air line from it and see if air comes out when you release the park brake.
     
    Inderjit, Jan 6, 2021
    Inderjit, Jan 6, 2021
    #36
  9. Jan 6, 2021 #37
    Akkaid

    Akkaid Bobtail Member

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    Oct 26, 2017
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    Fixed.
    The switch in the picture above was the parking brake switch. Someone used an adapter to make it fit, but the adapter pushed it out too close to the dash. One of the wires was sitting on top, right between the dash and post. Over time it wore bare and kept the circuit closed.

    I tested all the switches, but with the parking brake on, so never thought to see if the circuit would open. It does not show in the ecm on a laptop as a part of cruise control, so the technician did not see it either.

    If anyone else reads this like I did trying to fix your cruise, the wiring diagrams in the forum are awesome.

    This is the 1000th reason I hate when people jury rig trucks, take the time to get the right #### part.
     
    Akkaid, Jan 6, 2021
    Akkaid, Jan 6, 2021
    #37
    11225, schmidt107, Oxbow and 2 others Thank this.
  10. Jun 1, 2023 #38
    11225

    11225 Bobtail Member

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    May 28, 2023
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    I know this an old post but good info. Same issue with my truck.
     
    11225, Jun 1, 2023
    11225, Jun 1, 2023
    #38
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