Allison automatic code P0842 stuck in gear?

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by mixingconcrete, Jan 19, 2021.

  1. mixingconcrete

    mixingconcrete Bobtail Member

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    Apr 14, 2019
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    Hello, we have a 2015 western star 4700sf with the allison automatic in it and driver says he was driving and all of a sudden transmission wont shift so he is stuck in that gear. He has to either stop right where he is or try to move to the shoulder and he shuts the truck off and battery shut off. Turns it on and it resets it and he can drive again. keeps happening more often now. Does anybody know what could the problem be? Transmission was rebuilt about half a year ago.
     
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  3. Inderjit

    Inderjit Light Load Member

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    Sep 17, 2017
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    What model of transmission?
     
  4. mixingconcrete

    mixingconcrete Bobtail Member

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    Apr 14, 2019
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    Its a 4000rds
     
  5. Inderjit

    Inderjit Light Load Member

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    Sep 17, 2017
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    From a code list I found on Allison's website.
    P0842 Pressure sensor low voltage PS1.
    The pressure sensors are internal. The problem could be a broken wire
    corroded connection or possibly a failed TCU.
     
  6. mixingconcrete

    mixingconcrete Bobtail Member

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    Apr 14, 2019
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    I ordered the oil pressure sensor and harness that goes inside the transmission. Hopefully that will fix the problem.
     
  7. Inderjit

    Inderjit Light Load Member

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    Sep 17, 2017
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    Have a good look at the harness between the transmission connector and the TCU.
    Low voltage at the sensor can be a broken power wire to the sensor in the harness.
    You will need the gaskets as well. Allison TCUs do fail I have changed a few over the past few years.
     
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