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  1. #1

    Default Need a little help from you cheby guys.

    Son-n-law has an early 2000's vintage(2000, 2001, 2002) 1500 GMC 4x4 (top model) maybe sierra? v8 gas engine.
    Transmission shifts normally in hi range, 2 or 4wd, but won't shift out of 1st when t-case is in lo range?
    What the heck. and where the heck to look at/check?

  2. #2
    Legend

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    Default

    Meaning you have it in overdrive and it wont shift out of first or the shifter wont move from first? Using 4lo is tricky, its not intended for everyday use, its also meant for VERY slow speeds, like 5MPH, I would first find out exactly what the truck is and then get the owners manual (it should say the year on the manual, if you still have it) and read up on operating in 4lo.
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  3. #3

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    Shift lever works fine. When lever is in D(O), tranny stays in first and doesn't upshift.

  4. #4
    Legend

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    That could be the design of it, my truck runs around 2000RPM in 4 lo and in OD

  5. #5
    Legend s5belford's Avatar
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    Default

    correct me if I'm wrong but I don't think 4-lo is meant for shifting into second, its such a low gear with a low speed. does everything else work fine?


    S.BELFORD

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  6. #6

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    Quote Originally Posted by s5belford View Post
    correct me if I'm wrong but I don't think 4-lo is meant for shifting into second, its such a low gear with a low speed. does everything else work fine?
    All else is fine. The other auto 4x4's he and I have owned shifted up through the gears in lo range, so we were expecting this one to as well. Maybe not?!

  7. #7

    Default

    No, the transmission should shift through the gears fine (mine shifts a little harsh in low range because of the gear redcution, but it definitely shifts).

    Do you get any engine lights or anything like that? The transmission is electronically controlled, so it's up to the PCM to tell the transmission to shift. And it's up to the transfer case to tell the PCM that it is in low range. My first thought is that this "signal" that tells the PCm that you've shifted to 4L is somehow not reaching the PCM, so the PCM is waiting for normal high range speeds to shift (which you never get to because you're in low range/1st gear).
    Last edited by MrShorty; 10-13-2009 at 10:27 PM.
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  8. #8

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    He hasn't mentioned a CEL/SEL but I'll verify. My first comment to him was that it seemed the PCM didn't know it was in lo, but I can't find a switch or senor as of yet that may send that signal.

  9. #9

    Default

    Quote Originally Posted by RatherBNtheWoods View Post
    Son-n-law has an early 2000's vintage(2000, 2001, 2002) 1500 GMC 4x4 (top model) maybe sierra? v8 gas engine.
    Transmission shifts normally in hi range, 2 or 4wd, but won't shift out of 1st when t-case is in lo range?
    What the heck. and where the heck to look at/check?
    It sounds like it's losing the speed signal in low range. It should up-shift in low range just as it does in hi-range. The easiest way to see what's wrong is to hook up a scanner and drive it in low range. You can then watch the VSS, MLP, Transfer Case Range and Mode PIDs and see what's going on. If for instance the scanner is showing no VSS or Low range on the MLP the transmission will not shift.
    Jim

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