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  1. #1
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    Default TAP Shift problems

    2004 GTP Comp G, 120K miles.

    Recently, when shifting into "M", the car doesn't recognize that this selection has been made, and just continues on in D (neither the DIC nor the HUD show the gear # (1,2,3,4), which they normally would when shifting into manual mode). If I slam the gear shifted into M when shifting from D, it usually does work. There is nothing wrong with the paddles....it's all the gear selection.

    I thought that the gear shifter might have an electronic switch that recognizes the difference between D and M modes, but apparently this isn't the case. So, that leaves with what options?

    - Is the "switch" completely inside the transmission? That would be out of my league for repairing.

    Is is possible the the gear selector is not quite pulling the cable far enough to engage the M mode? Is there a cable adjustment that can easily fix this?

    I do have another TAP shift shifter from a salvage yard (because I initially thought that the shifter would have the issue...again, apparently not).


    Any thoughts/advice is appreciated , as I haven't been able to find any other info on this particular issue.




    More info: I just went out to look around and go for another drive. Here are some more oddities with the shifter:

    - When you put it in reverse, the "R" on the DIC/HUD will show/disappear if you wiggle the shifter lever forward and backward (but never out of R). The transmission totally stays in reverse, regardless.

    - If you shift into "D" from "N" while holding in the button on the shifter, the DIC/HUD displays "D". If you shift into "D" from "N" without pressing in the shifter button, it the DIC/HUD does NOT show "D" (however, the car still shifts into drive and otherwise drives normally).

    - If you shift into "M" and do not get any response from the car on the DIC/HUD acknowledging that, the TAP shift paddles do nothing. The car drives normally as if it is in "D" mode. However, when shifting back to the "D" position, the "D" lights up on the DIC/HUD, indicating the the car knows you shifted back into "D" mode.

    What is going on here? The transmission seems to know what gear you have selected (aside from M mode), regardless of what the DIC/HUD indicates. However, assuming that the DIC/HUD is a good indicator of what the ECM knows has been selected, apparently "M" mode only works via software/electronic means controlled by the ECM (which makes sense, since the paddles have no mechanical influence whatsoever). So, where is the problem. The only other oddity in the car whatsoever is that a low washer fluid warning comes on all the time at startup (I figured it was just a back fluid level sensor for that, and I don't care about it).
    Last edited by goldcamj; 3 Weeks Ago at 02:36 PM. Reason: more info

  2. #2
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    Default Re: TAP Shift problems

    I think I found my answer: "The Internal Mode Switch (IMS), located inside the transmission, is used to enable or disable TAP operation on Grand Prix (W body) applications."

    http://www.atraonline.com/gears/2007...2007_10_46.pdf

    I guess I'm screwed. I wonder if the car will still operate in P/R/N/D if the IMS is totally shot (which apparently is the direction it's heading.).

  3. #3
    GT Level Member Gregorius's Avatar
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    Default Re: TAP Shift problems

    I would look at wire harness problems, specifically corrosion in the main plug that goes into the trans. Maybe the shift linkage is a little loose, either in the console or to the tranny?

    The wiring diagram for the entire car is in the Full Service Manual. Available as a PDF from.. Here.

    Magic Link to WarStryker13's google drive

    https://drive.google.com/drive/folde...nN3SVBBWmlkTnc
    Magic Link to WarStryker13's Google drive


    ... our lady of blessed exceleration, don't fail me now ...

  4. #4
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    Default Re: TAP Shift problems

    Thanks for the link. I'll look into the electrical connector, but I think of the two options the shift linkage is more likely (although I'm still betting it's a failing IMS in the trans). I looked through the service manual you linked and can't find any info on the shift linkage. Does the linkage on the transmission end just pop right of the stud on the lever on the trans?

  5. #5
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    Default Re: TAP Shift problems

    Problem solved, I think. I adjusted the shifter cable (~ 1/4" more length at the adjuster under the hood), and it seems to be working correctly now. The gear selections seem to be a little "crisper" too (not the actual shifts....just the shifter).

    Thanks!!!!

  6. #6
    I can't car too good. SaukRapids's Avatar
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    Default Re: TAP Shift problems

    Sometimes if it gets towed, the driver might just move the cable to get it out of gear. They're typically less skilled at putting it back together correctly. Ask the male meter maid how I know, lol

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