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C4500 Transmission won't shift

Discussion in 'Chevy Trucks' started by dgterp, Jan 25, 2013.

  1. dgterp

    dgterp Junior Member
    Messages: 6

    Duramax with Allison tranny. Check engine light just came on. Seems like transmission won't shift out of second gear. Any thoughts.
  2. Moose's Mowing

    Moose's Mowing Senior Member
    from SE PA
    Messages: 198

    I believe that transmissions will turn on the check engine light if the computer is picking up a code/fault. Maybe plug in a scan tool and see what it says? That outta give you a better starting point. good luck
  3. GMC Driver

    GMC Driver Senior Member
    Messages: 740

    Only issue we've ever experienced with the Allison was something similar (except it was 3rd gear) - ended up being a shift solenoid. A scan should help you out, it will register a code.