Thread: 2005 Pontiac Grand Prix Motor and Trans Issues

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  1. #1 2005 Pontiac Grand Prix Motor and Trans Issues 
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    I have a 2005 Pontiac Grand Prix with 212,000 miles on it that I bought a few years back, and for the most part it has been fairly reliable. Over the course of those three years the only major things done besides basic maintenance is replacing both rear struts, replacing the coolant reservoir, exhaust flange off the manifold, and replacing the power steering pump with both high and low pressure lines.

    About a year ago I had to replace the low pressure line on my power steering pump when it had a hole worn through it by one of the shields in the passenger side wheel well, and so when I did that I also figured I might as well replace the high pressure line along with the pump itself since it had right at about 200,000 miles on it. Since doing that, my steering has seemed to be noticeably stiffer, and it doesn't steer as easily or smoothly as it used too. It also has had a leak that I haven't been able to find the source of it since then (typically runs almost completely empty within about two months if not filled regularly. One thing did notice is that the passenger side rubber boot on the rack and pinion is torn the whole way through. When you start the car after sitting for awhile it will turn normally the way it used too, but once the car warms up it goes back to being stiff and almost notchy at times. Wondering if maybe it has a bad rack and pinion in it since it's never been replaced or maybe this could be caused by a leak somewhere?

    Another problem I have with the car is that over the last 2-3 thousand miles the motor has started surging when under light load under highway speeds, typically occurring when going up small inclines or lightly pressing the gas to speed up a little. It will typically surge about 500 rpm or so, mostly around 1750-2250 rpms. I have caught it doing this is mostly overdrive but will sometimes occur in 3rd gear. It has seemed to get worse over time, as when it started it was fairly hard to get it to do this on my own, but now it occurs almost constantly, even at lower speeds now (around 30-45 mph). I have also had a problem with it running like it's down a cylinder from time to time, most often happens when it's colder. It will constantly lug itself around, and feels a little bit weak, but goes away normally if you turn the car off and let it sit for a few minutes. I have replaced the MAF sensor hoping this would fix the issue but it hasn't, and I also had to clean the throttle body out when I first bought the car because it was full of soot and would need a little throttle right after you started it to keep it running. I have hooked a code reader up to it a few time since the check engine light has been on since I have owned the car, and it only brought up a low catalyst efficiency code for the longest time which I figured was just a bad o2 sensor, until recently it started throwing a code that has something to do with the engine not heating up properly, although I have never noticed any problems with that. I can provide code numbers if needed. I bought the car with 174,000 miles on it and don't when the last time the spark plugs have been replaced, and I also don't know if the wires have ever been replaced either.

    The final problem I'm having with the car is that it will occasionally shift very harsh in and out of 2nd and 3rd gear. Noticed the problem at about 180,000 miles. It seems to occur after the car has been running and driving for a longer amount of time, typically around about an hour if not more. It doesn't happen all the time but if I'm driving for around an hour or more, three out of five times it will occur. I have tried topping off the trans fluid to see if that could be the issue and it never changed anything. I have read that it could be build up caught in the trans, or possibly something to do with the trans filter, but I have never actually looked into that. I can get it to stop doing this if I stop and shut the car off for a few minutes, sometimes I'll ever shut the car off and then turn the ignition on so I can shift through all the gears without the car running. Once doing this it will go away but will typically start doing it again within about half an hour if I don't let it set for an extended period of time.

    I haven't done any modifications to the car except for installing a high-flow resonator and replacing the original muffler with a Cherry Bomb one. Any help or suggestions would be greatly appreciated!
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  2. #2 Re: 2005 Pontiac Grand Prix Motor and Trans Issues 
    Solving problems BrandonHall10's Avatar
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    Quote Originally Posted by mboles18 View Post
    The final problem I'm having with the car is that it will occasionally shift very harsh in and out of 2nd and 3rd gear. Noticed the problem at about 180,000 miles. It seems to occur after the car has been running and driving for a longer amount of time, typically around about an hour if not more. It doesn't happen all the time but if I'm driving for around an hour or more, three out of five times it will occur. I have tried topping off the trans fluid to see if that could be the issue and it never changed anything. I have read that it could be build up caught in the trans, or possibly something to do with the trans filter, but I have never actually looked into that. I can get it to stop doing this if I stop and shut the car off for a few minutes, sometimes I'll ever shut the car off and then turn the ignition on so I can shift through all the gears without the car running. Once doing this it will go away but will typically start doing it again within about half an hour if I don't let it set for an extended period of time.
    Sounds like you've tripped a P1811 code. Next time you get the harsh shift, scan for codes before you shut the car off or cycle the key to confirm. That code resets when you shut the car off and (IIRC) does not light the MIL. Basically, the trans is wore out. The computer senses that the trans is taking longer to shift than it should, and sets max line pressure. Google P1811 for more detail. A trans-go shift kit as a band aid, albeit a very good band aid.
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