99 Sierra 1500 shifting problem

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by 1999Sierra, Jan 9, 2009.

  1. 1999Sierra

    1999Sierra New Member


    I'm new to the forum but have been a long time GMC truck owner.

    My 1999 Sierra 1500 4 X 4 SLT Z71 with 135,000 miles on it doesn't want to shift gears when the temerature drops below freezing.

    It will stay in 2nd for about a mile then shift t 3rd. After another couple of miles it will then shift to 4th and, again, after another mile or so shift into overdrive. After this it will then shift fine.

    I've recently had the ATF drained and refilled with Dexron 3.

    I'm hoping somebody can help me fix this minor issue as, apart from this problem, the [COLOR=blue! important][COLOR=blue! important]truck[/COLOR][/COLOR] looks and run great.


  2. 04sierracrewcab

    04sierracrewcab Epic Member 5+ Years 1000 Posts

    Welcome to the site!
    Hopeully the "tranny" guys will chime in on this.
  3. tlperry68

    tlperry68 Epic Member 5+ Years 1000 Posts

    Can you try putting the truck through the gears manually i.e. 1 , 2, 3, Drive with OD off? Or what ever you cn. But that is one weird problem, I've never heard of it.
  4. grsemnky63

    grsemnky63 New Member


    try a tps sensor
  5. 1999Sierra

    1999Sierra New Member

    Hi and thanks for the suggestion. What is a "TPS" sensor?
  6. 1999Sierra

    1999Sierra New Member

    Thanks for the suggestion. I have done that and it shifts into first no problem and second no problem but when you selct 3 or 4, if the temerature is below freezing, it will hang up in second gear. After a couple of miles it will then go into third gear and, agter another couple of miles, it will go into fourth.

    When the temerature is ABOVE freezing it shifts through all gears real smooth with no problems at all. Weird huh?
  7. retired

    retired Rockstar 100 Posts

    TPS, throttle position sensor.Don't replace it thats not the problem, I think he meant to say speed sensor. Could possibly be the speed sensor but this on is difficult to diagnose.
  8. 1999Sierra

    1999Sierra New Member

    Thanks RETIRED. I'll check with the local GMC dealer (if he's still in business!!!) for a spped sensor but I still can't figure out why it would be temerature sensitive. Still, it's worth a shot.

    Any more ideas?
  9. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    Because the transmission is fully electronically controlled, my first question on these problems is, is the problem with the computer telling the transmission when to shift, or is the transmission not responding correctly when commanded to shift. You might pull codes from the PCM to see if there are any trouble codes that give any direction. From there, you would need one of the more expensive scanners (that can access transmission information) and watch to see if/when the PCM is commanding shifts and if the transmission is responding correctly.
  10. retired

    retired Rockstar 100 Posts

    Cold temps will effect sensors especially if they have water or oil getting into them, see if you have any oil coming out of the speed sensor plug.

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