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Thread: Shift Denied.

  1. #1
    Tuner in Training
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    Shift Denied.

    I have a 6L80 in a 2011 Camaro. When autocross'ing the car and using the paddles in S mode, I'll often get a Shift Denied when trying to do a 2>1 downshift.

    I'm confident the shifts would be safe if allowed, but for whatever reason, the computer says no.

    I've also had this happen on 5>6 upshifts, when, apparently, I wasn't going fast enough.


    I'm assuming this is a speed related issue?

    Is there a particular table, or tables, I should be looking at to try and remedy the 2>1 denied downshift?

  2. #2
    Advanced Tuner IARLLC's Avatar
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    Did anybody find an answer to this? I am tuning an 8L90E in a 2017 Rally Race truck and really want it to up/down shift when hitting the button. After some messing around I am much happier with the shifting and manual control but when downshifting 4>3, 3>2, or 2>1 I get shift denied message. Maybe we are missing a table or the BCM is limiting based on its criteria?

  3. #3
    Tuner MakesBadDecisions's Avatar
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    I have to think the BCM has a major role in the TUTD. It seems like no matter what I do, I can not get the TUTD to stay in lets say 5th let RPM come down to 2000 RPM and smash the throttle and it down shifts every time.

    I have my Transmission-General-CMD Gear Control Limits set to 5500 RPM and mine will down shift to 5500 if I time it right. Too soon and denied pops up, keep hitting button until it finally goes.

  4. #4
    Advanced Tuner IARLLC's Avatar
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    Part of this might be a mismatch. New T87, 2015.5 Yukon Denali L86/8L90E OS in a 2017 Silverado L86/8L90E. The Yukon might have an additional shifter position or something. No matter what I do it does not tap down to 3rd, 2nd, or 1st. Just shift denied.

    Thanks to so much good info on here there have been loads of improvement in the trans....but I would really like them to have the ability to downshift manually for control and braking. Actually I have not tried it in tow/haul yet. I should give that a shot.

    With some adjustment it let me hold 1st or 2nd until I hit the rev limiter. I later changed that to let it shift at the last possible moment (just in case after 6 grueling days in the desert somebody forgets to hit the button).

  5. #5
    Advanced Tuner IARLLC's Avatar
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    Found it!
    In an attempt to keep the truck from automatically downshifting at lighter throttle in TUTD mode I had set the Part Throttle Shift > Downshift Speed vs TPS vs Shift-TUTD too low. Instead of keeping it from downshifting automatically it seems the table kept me from downshifting manually for braking/control. It is still messing with my head. We are generally used to tables that tell it how to control the automatic functions. This one appears to allow or deny manual requests.... One way or another after a little more sleep I moved those up enough to allow manual downshifts for low throttle control/braking.

    It does not allow me as much TUTD control as we have with earlier 6L80E/90e rigs...still downshifts automatically while in TUTD. It seems to me that until we crack BCMs we will just have to live with that.

  6. #6
    I agree, the BCM needs broke into.
    That little SOB takes all the fun out of these new vehicles. I get that 98% of the human race should probably not drive let alone be able to turn babysitters off. The other 2% of us like to power slide the corners, burn the tires off in true redneck fashion and generally make as much noise as possible.

    With that said the TUTD auto downshift is lame AF. I have so many TUTD revisions it makes me mad to think of how much time I have wasted.

    I did see that there is a guy working with the diesel guys and has the BCM doing some cool stuff. Launch control, gauges and some other cool features on the MyLink display.

  7. #7
    Advanced Tuner IARLLC's Avatar
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    MMMMMMMMM! Interesting! I have to look back in to that.

  8. #8
    I have emailed him twice with no response. https://www.btdieselworks.com/collec...-2019-autosync
    I would guinea pig the shit out of this.

  9. #9
    Advanced Tuner IARLLC's Avatar
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    That autosync is crazy! The way I understand it their BCM work was a bit of a joint venture with OZTuner and of course some cooperation from some kind of fuel injection tuning company...

    None of them seems to offer options for the newer GM stuff yet. White Auto and Media say they can do newer BCM work but I don't know that they have gone all of the way into BCMs' affects on TCM stuff. It does seem like a profitable direction though with so many people wishing their 8L90E TUTD responded like a VETTE with commands going straight to the TCM instead of via BCM....

  10. #10
    I got the same impression, they use the "other" software. I do know that the "other" software does have some BCM access, more like user defined parameters.

    It seemed like these guys got a good part of the BCM figured out and if they got that far how much further is there? Probably a metric shit ton.

    I have several clients that would love better TUTD functions, longer remote start times, kill the stabilitrac completely by button to not come back at 35mph, ability to edit TPMS, power window features, camera features, etc, etc, etc....

    If I were only smarter.