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Thread: e38/t42 communication

  1. #1
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    e38/t42 communication

    Having some trouble with data/trans in limp mode. This is a 72 blazer that came into shop to finish for customer. harness is made by Modern vintage.(still waiting on a reply from him about wiring diagram.) Engine OS is 12630501 Trans is 24236195 engine starts and runs fine. data looks normal on ecm side for the most part---3 things I noticed--speed reading 158mph, trans showing in gear, brake switch shows invalid. On tcm side, vehicle speed reads correctly, as well as brake switch, however most data looks like something is unplugged. (tft=-40, no engine rpm,etc.) trans has 12v on pin E. no trans codes. ecm has a few codes looks like related to the swap. not sure what to look for next, any help is appreciated. I can command first and second gear with scan tool

  2. #2
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    E38 ECM OS 12630501 was used in 2009 by Truck, SUV, and full-size van.

    T42 TCM OS 24236195 was used in 2005 by Pontiac GTO.

    This mismatched ECM and TCM paring will not communicate.

  3. #3
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    Quote Originally Posted by Jon S. View Post
    E38 ECM OS 12630501 was used in 2009 by Truck, SUV, and full-size van.

    T42 TCM OS 24236195 was used in 2005 by Pontiac GTO.

    This mismatched ECM and TCM paring will not communicate.


    thank you for reply. so my best bet is to look for another tcm? out of an 09 ? Or is current tcm programmable to work? thanks again

  4. #4
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    It sounds like this project has made its way to you - which is never any fun.

    Unplug the main transmission connector. Count how many wires (terminals) are in the wiring harness. Next, count how many terminals (pins) are in the transmission itself (corresponding connector) - have may have to use a mirror for this job.

    So, first sort out what 4L60 transmission version you have, then program the T42 TCM accordingly.

    If the transmission itself has only 13 pins - then it is a Gen 3 version with no ISS - and it's going to be a problem.

    As long as the transmission itself has 15 or 17 pins (Gen 4 version) - then reprogramming the T42 TCM may get you going.

    If it the transmission has 15 pins, then program the T42 TCM as a 2008 truck - you may also need a different E38 ECM (and programming).

    If it the transmission has 17 pins, then program the T42 TCM as a 2009 truck - and your current E38 ECM should be OK to use (in this case).

  5. #5
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    Right on, thanks for the info. I appreciate it.

  6. #6
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    where would I find a stock tune for 2009 Yukon tcm? (t42)

  7. #7
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    trans has 17 pins, harness has 15

  8. #8
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    Quote Originally Posted by aarond View Post
    trans has 17 pins, harness has 15

    That is a problem.

    You will need to add 2 additional wires between the transmission connector and the T42 TCM.

    Also, the transmission connector and the T42 TCM are pinned differently for a 2009+ 17-pin 4L65 - versus a 15-pin 2007 / 2008 4L65.

    This means that several existing wires will need to be moved.

  9. #9
    Senior Tuner Frost's Avatar
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    -09 and up use internal mode switch and ISS. Being clever on the cal side, you can get an older 60 with no ISS to work properly in both 07-08 and (usually) in 09-up platforms as long as they were OEM 4-speeds.
    Steve Williams
    TunedbyFrost.com


  10. #10
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    I seem to be making some progress, but still having issues. Unsure if wiring related or internal trans. I now have a t42 tcm with OS 24239927. I also have added two wires to harness and moved a few around. It looks as though harness was made for an 08..anyhow here is new pinout, maybe im missing something. Thanks in advance for any help.

    TCM---------------------------TRANS
    1-----------------------------U
    2-------------------------------A
    3-------------------------------K
    5-------------------------------pin 71 ecm
    6----------------------------data bus
    7-----------------------------data bus
    16----------------------------speed sensor "A"
    17-------------------------------D
    20--------------------------------B
    23--------------------------------H
    25--------------------------------T
    29--------------------------------F
    30--------------------------------M
    31--------------------------------key power
    32--------------------------------bat power
    35--------------------------------L
    37---------------------------------data bus
    38--------------------------------data bus
    39---------------------------------J
    40---------------------------------C
    41----------------------------------speed sensor "B"
    42--------------------------------brake switch
    45--------------------------------V
    46--------------------------------G
    49-------------------------------ground
    ground-------------------------N
    ecm pin 1---------------------W

    I now am showing correct speed, as well as in or out of gear. i can also read rpm through trans side. tft still shows -40. no shifting, have dtc p0961, hard code. do these pinouts look correct for this year/operating system? thanks!

  11. #11
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    Is this the only way to make a ly6 work with a 4l80e? Thanks

  12. #12
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    I have heard that some express vans from 2008 have a ly6 and a 4l80