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Discussion in 'GM Allison' started by 4wdaaron, May 10, 2008.

  1. 4wdaaron

    4wdaaron Hard Worker

    What have you guys experienced when the NBSU goes bad on your duramax..

    My dad's '02 LB7 has no reverse sometimes, but cycling the ignition brings it back.

    Service Engine light is on and had the ECM read: that p0700 (can't remember it exactly) came up, which is just a general code saying something is wrong in the TCM right?

    Is there a code set in the TCM I need to have read, if so what am I looking for?
  2. blizzardplowman

    blizzardplowman Crowd Control Staff Member Moderator

    May 3, 2008
    SE WI
    First thought is the ignition switch...... The NSBU will send a error message of shift range inhibited in the DIC...
  3. emerson

    emerson Ugly is cheap

    May 9, 2008
    Prince George BC
    You are right about the TCM 700 code, it is just says there is a more specific tcm code if you get the right reader. I can get one from Canadian Tire (chain hd ware store up here) for $179 that will read and clear TCM codes. My Predator won't do anything but show TCM700. The first thing that happened with my NSBU was the line under the gear didn't always display, it was sometimes limited the 3rd gear, and the forward/reverse engagements were rough. After a few days the CEL went on and then at the end the shift range inhibited message showed on the DIC. If you have to replace the NSBU, get it from an allison dealer. GM wanted $255; allison $83.
  4. 4wdaaron

    4wdaaron Hard Worker

    Yea the forward and reverse shifts are taking longer and longer. Plus, when it locks into reverse it's rougher than ever before. It's also becoming more frequent that there's no reverse and the power has to be cycled. Haven't seen the "Shift Range Inhibited" DIC warning yet. Thanks for the warning on the prices.. I had read that at that "other place" awhile back.

    My question still is what is the TCM code for the NSBU?

    I sure hope its not something more serious??:confused5:
  5. schulte

    schulte ACCELLERANT!!!

    May 4, 2008
    Southern CT
    It should say "range shift inhibited" for NSBU, not "shift range inhibited".
  6. Philbilly2

    Philbilly2 Just a speck on the wall

    I have seen the gear indacator lights not work, I have had my truck go into gear so hard I though it was going to snap an input shaft, I have had my truck not start, I have had no control over shifting, I have had the range indactor reading.

    I have seen quite a few things happen!
  7. 4wdaaron

    4wdaaron Hard Worker

    Yup it's getting harder on the shifts the longer it goes... I really need to get that
    TCM read ASAP! I hope to know something more sometime before wednesday.
  8. 4wdaaron

    4wdaaron Hard Worker

    Got one coming tmw... hopefully it works cuz there's no more reverse! Sounds like there might be a supply issue also since a lot of places don't have any, particularly short for the '02's for some reason.
  9. 4wdaaron

    4wdaaron Hard Worker

    Got new NSBU installed after the hard-to-remove connectors and filing on a burr... the instructions say it's important to clear the code before starting up, but we don't have a programmer so fired it up and still blinks in reverse sometimes. Hopefully that will go away after we get the code cleared???
  10. ripmf666

    ripmf666 Registered user

    May 10, 2008
    Kansas City Mo
    could try unhooking batteries for a hour or so
  11. modified

    modified modified

    May 16, 2008
    NE Wisconsin
    Hope you had the trans in NEUTRAL during the install.
    I coated connectors with dielectric grease to keep moisture/corrosion out, and mine's been working fine for about 5 years.
  12. 4wdaaron

    4wdaaron Hard Worker

    got her fixed... code was po743... tcm wasn't bad.. TCC Solenoid was bad.

    Thanks for your help guys!

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