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Thread: Allison 6spd TCM versions

  1. #1
    Forum tyhee Site Admin GMPX's Avatar
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    Apr 2003

    Exclamation Allison 6spd TCM versions

    Many thanks to forum member vectorbundle who posted a fantastic summary of the various Allison TCM models in another thread that was worthy of becoming a sticky.
    In summary it sounds like you need to be very careful when using SPS to flash these TCM's to ensure you've made the correct selections or you'll brick it, although in some cases it sounds like SPS will just brick the new TCM anyway!

    vectorbundle wrote:
    A41 is not for GM pickups or MD trucks, forget it.

    T14A (GM serv #24256864 on sticker, part #24256671 and T14A on the case) is Delco branded version of Allison A46 (part # 29546675 and ATA4601 on case). they are the same hardware.

    T14 (GM serv #24256861 on sticker, part #24256670 and T14 on case) is Delco version of Allison A50 (serv #25978353, part #29545535).

    T14 is to A50 what T14A is to A40 -- sort of. there are some differences that are part of the boot level. SPS does not write to that, it only writes the OS and trans cal segments.

    when you flash an 06-08 GM pickup with SPS you must select the TCM type (list of part/service #s that just determine if it's T14A/A46 HW or A40). the cal segment for 08 will be the same 24257976. the OS will be different 29541751 (A40), 24256580 (A46). cross flashing will brick. you will find similar pattern when selecting A50 vs T14 for 09-10 pickup -- same trans cal, different OS.

    you cannot SPS an A50 selection into a T14, it will brick. generally you cannot flash a file you read out of an A50 with EFIlive into a T14, it will brick. just as flashing A40 OS and cal into an A46 will brick. in some cases i can recover them.

    for some strange reason for 2011+ GM pickups the same GM flash works in A50 and T14 (at least that used to be case, they may have made some "improvements"). i haven't figured out yet why that is, i don't have any A50s left to test stuff on and generally have no reason to use them.

    there are a couple of problems specific to SPS and MD trucks. GM never updated their MD Allison A40 and A50 software for T14A and T14. there IS no MD calibration in SPS for the new controllers. and there is no TCM hardware selection screen. so people install a new T14A in their 08 MD trucks figuring GM says it's a replacement for an A40 and flash it for an 08 MD VIN... brick. SPS a T14 in 09 MD truck... brick.

    what's worse, SPS also bricks an A50 when flashing for an 09 MD truck (that's an error with SPS, it's not a problem with the controller). A40s flash OK for 06-08 MD VINs. but as far as EFIlive is concerned, as long as one flashes only what was read out of a TCM with the same HW, there is no problem. there is no fundamental flaw in the T14 or T14A TCMs. the fundamental flaw is GM's support and documentation.

  2. #2
    Lifetime Member Move'n Up's Avatar
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    Oct 2015


    Great, thanks for sharing that information!
    2006 Ram 2500 4x4, 5.9 CTD, Laramie, QC
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