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Thread: Trans Shift Mode is always 4WD - NAG1 2015 JKU

  1. #1
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    Trans Shift Mode is always 4WD - NAG1 2015 JKU

    I'm starting to troubleshoot some shift issues I've been having and noticed that the Trans Shift Mode is always 4WD. How is this determined by the PCM/TCM? My initial thought was the Transfer Case Switch but it reads correctly.

    The 4WD mode explains why I'm having issues with it not always downshifting to 1st when I come to a stop so I think its a good place to start troubleshooting. Log from this morning attached.
    Attached Files Attached Files

  2. #2
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    Here's a new read of the tune as well. I really don't see anywhere for the mode to be set to 4WD, though I have seen it on other vehicles
    Attached Files Attached Files

  3. #3
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    I haven't seen a 5 speed JK yet that didn't say 4WD in trans shift mode. What size tire and gear ratio are you running?

  4. #4
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    Quote Originally Posted by Mag0842 View Post
    I haven't seen a 5 speed JK yet that didn't say 4WD in trans shift mode.
    Yeah, that's kind of what I have been gathering the more I look into it. What I still can't figure out is how the PCM and TCM know to change shift behavior in 4Lo. Can't seem to find a PID that changes when it is put into 4Lo but I am almost positive that the shift behavior was different in 4Lo previously where it wouldn't downshift to 1st, you had to switch to autostick and put it in 1st manually.

    Quote Originally Posted by Mag0842 View Post
    What size tire and gear ratio are you running?
    5.38's, 40's, Edelbrock SC.

    Had lots of help from @Hemituna as well as my local dyno tuner/friend to get it running as good as it does. I suspect I may have an issue with a valve body or something that is causing it to not downshift to 1st all of the time.