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Hard shifts in Pontiac Grand Prix GT

I own a 2002 Pontiac Grand Prix GT with 79,000 miles. In the past year, I've started to have problems with hard shifts, and from what I've heard, this is normal with the amount of miles I've driven. What I've been noticing though, is that the car only shifts hard after the engine has been running a while. For example, sitting in sit and go traffic. If its cold outside (under 30 F or if I drive with out stopping a whole lot) I never have the problem. Is there any hope other than rebuilding the transmission? I've tried those fancy additives and they haven't helped.


  • edited December 2008
    The problem might not even be the transmission. The computer monitors sensors on both the engine and transmission. Some of these sensors, if faulty will cause the computer to command full line pressure from the transmission pressure control solenoid. When at full line, the transmission will shift harsh, this is good and protects the transmission from destroying itself. Where I would start is a scan of the computer for any trouble codes. Like I always say, "Dont condemn the transmission just yet"

  • edited December 2008
    So you're saying that if I rented one of those computers that plug into the diagnostic port on the car, I should get some sort of code showing up? Would that code be there only when the car was shifting hard or would it still be there when it was running "normally"?
  • edited December 2008
    You can have it checked now to see if there are any stored codes but if I were you I would wait until it starts shifting hard then immediately (Without shutting off engine) take it to one of your local auto parts stores. Most local parts stores will scan for free. Get the code/s and post them back with us and we'll go from there.

  • edited December 2008
    Alright, I'll do that. However, if the current trend continues (where it only shifts hard when it's warm) it might be awhile as the current high is only supposed to be in the 20s-30s for a while. I'll post the results when I get them. In the mean time, is temperature something that could affect this?
  • edited December 2008
    We had the same issue with our '01 Olds Intrigue (HARD shift when hot) which I think uses the same transmission as your Grand Prix: 4T65E. When you say: "shifts hard", do you mean like the whole car shudders? When our car did that, it felt as if the trans was going to fall out of the car!
    The dealer replaced the PCM and it solved the problem.
  • edited December 2008
    Exactly. How hard it shifts varies, but it does seem like the transmission is ready to fall out of the car. Some of the times I feel the urge to turn around and make sure it's not laying on the road behind me. What is a PCE exactly?
  • edited December 2008
    I'm sure that your scanner will scan any control module (computer) on the car; but, I believe that what tgtcat6 needs to have scanned for codes, is in the TCM (Transmission Control Module). Most engine OBD II scan tools (which the auto parts store has) will only scan the engine computer (ECM, or PCM), not the TCM.

    You may have to go to a transmission shop to have the TCM scanned (for a fee).

    PCM = Powertrain Control Module (engine computer) is the same as ECM = Engine Control Module (engine computer).
  • edited December 2008
    Interesting. Does any one have a rough idea of what a PCM would cost to have replaced? One transmission shop quoted me upwards of $1500 to rebuild the transmission. Is it something that a do-it-your-selfer could do?


    Is this something that could vary with temperature like 65acura describes?
  • edited December 2008
    This hard shift problem is most likely an electronic control problem, your transmission should NOT need a rebuild. I don't recall how much the PCM cost, it was a couple years ago, but I can guarantee you it was less than $1500. Have the shop check out the sensors (like transman suggested) and the PCM, I'm pretty sure that's where the problem is.
  • edited June 2009
    I finally was able to get the car examined and they told me that it's the "pressure control solenoid". They say there's a TSB on it, so it's happened to other people.

    The solenoid itself is $58.19 and labor to install was quoted at $414.09. They also recommended a fluid and filter change. Total price would be $691.99 after tax.

    Just wanted to post an update in case anyone else comes across this. I'd like to thank everyone that posted for their help.
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