Thread: 01 GTP tranny problem

Hello all. I'm new to these boards and thought some of you may be able to give me a little insight. I have an 01 GTP with 115k on it (not sure what transmission this is). A while back the tranny started acting up. Under slow accelerations it would surge just a little bit. I had to point it out to my wife when she was driving for her to even notice. At the same time it also started shifting weird. Under normal acceleration from a stop it would shift into 2nd at about 2800 rpm roughly. Continuing to accelerate it would shift into 3rd somewhere around the same rpm. The problem is that each time it would shift it would only drop down about 200 rpm, maybe a little more. Finally, when shifting into 4th the car would drop down to 2000 rpm, then to 1800 rpm, then to 1500 rpm. What gives? The "good" thing about this is that it is a very consistent problem each time I drive it and when it does shift it shifts as smooth as it should, there's no roughness to it at all. I took it to the shop where they ran diagnostics on it but found nothing. I was a little surprised because my first thought was speed sensor or throttle position sensor. I would think running diagnostic tests would have caught it if one of these was the problem. I then put some cleaner in the tranny, then had it flushed. The problem is still there, although the surging appears to have stopped. I told the shop who did the work that it still isn't right and all they said is that I'll have to bring it back in so they can look at it. I'd prefer to have some idea of what the problem MIGHT be before taking it back in. I hate getting work done at these shops. I'm planning on keeping the car another year or so, maybe longer if I can get by.

I do not have performance shift

Thanks for the info trannyman. I appreciate all your help. I might have to try one of these books.

Judging by your explanation I'd say the rpm drops isn't as odd as I've thought all along. It does kind of match your description, except for, like you say, the step down in rpms while in 4th gear rather than a more gradual reduction. So maybe that isn't the part of the problem that I should be focusing on right now.

What is really bothering me more in the last day or 2 (I've been driving this car WAY more than I usually do) is that the rpm fluctuations under a slow acceleration while already in 4th gear seem to be getting worse. At first it was minimal and occur only on occasion. Now it happens all the time. For example, I could be going 65 on the interstate and slowly accelerate to 70. The car seems real sluggish (until the boost kicks in). Plus the tach is bouncing a little (less than +/- 50 rpm), thus making it feel like the car is surging. If I stomp on it to get up to speed I don't have the problem. As you know I don't have any experience here, but the more I read the more I have a theory that I have a torque converter clutch starting to go bad. Is the torque converter continually slipping then grabbing then slipping and that is why my rpms are fluctuating?

Is it possible this is a PCM/engine issue and not a transmission issue? Maybe the RPM surge is being caused by a faulty 02 sensor or other PCM data and the symptom just feels like the TCC is unlocking/locking?

I'm no expert, but could be you're barking up the wrong tree here? One clue is the sluggish feeling from 65-70. Are you actually feeling any surging, or just seeing it on the tach? Could be a failing cam sensor or crank sensor that's providing fluctuating tach readings and affecting performance as well.

I have the same problem. I have an 00 GTP. I'm interested in finding out what it is. If I'm under firm acceleration - everything shifts fine. If I'm driving at 40mph, it'll drive you nuts. The engine will moan up and down constantly like the torque converter is slipping in and out. Mine's getting to where I can't stand it, but I don't just want to throw money at it without knowing what's wrong.

Per the triple edge performance website...

Tach bounces up and down a few hundered rpm while cruising in lockup:
Another common problem / concern of this transmission and more pronounced with added engine power or higher mileage. This generally happens when the valve body has excess wear in the TCC valve area. Excessive fluid leakage in this area of the valve body causes TCC apply pressure loss and can lead to uncontrollable TCC operation which causes the engine rpm to bounce up and down a bit. This problem is noticed most after driving a while and speeds between 42 and 70mph and in 4th gear. There are other causes to this problem that can be from worn or shrunken teflon seals on the input shaft, a bad o-ring on the input shaft that seals in the torque converter, a faulty torque converter clutch, and even a bad pressure control solenoid. Another common occurance is a worn out sleeve in the channel plate that supports the input shaft. When this sleeve wears the input shaft will get chewed up where the sealing rings are and cause problems. Commonly code P0741 will be found in the pcm memory as a stored code and is described as Torque Converter Clutch Stuck Off. When this happens adaptives shifts are disabled, TCC operation is disabled, and 4th gear can be disabled. Generally a new or reman / repaired valve body will correct this condition and a new EPC solenoid is always suggested as well. The TCC/PWM solenoid is rarely ever at fault and I am yet to find one bad. Again the valve body is the common cure BUT not always the culprit and certainly not the whole problem after this has been happening for a while. Any time a torque converter fails there will be debris going back into the trans. There is a pressure relief valve in the channel plate that will collect debris from a bad torque converter and reduce cooler flow, cause trans to run hot, and greatly effect TCC operation and can destroy a new converter in a matter of miles if this isnt carefully inspected or upgraded. The best way to verify proper operation as commanded by the pcm is with a scan tool by viewing TCC slippage rpm, TCC duty cycle, EPC data, and checking any codes and making sure the engine is running properly and a misfire is not a false sense of a torque converter problem or shudder.

It sounds like the problem lies somewhere in this paragraph to me, problem is there is a ton of crap here. Again though, I'm heading back to the shop to get it checked out. Problem is, my wife is due to have a baby any day. When she does the car is going to sit a lot more, plus money is going to be tight so mine might not get fixed for a little while.

So if you can confirm that the engine is operating normally, it sounds like a trans rebuild is in your not-too-distant future

I've built cars from scratch, rebuilt manual transmissions, engines, etc. I wouldn't consider opening up an auto trans. There are too many things that can be wrong after you do all the work to install it. Then - you remove it again, open it up, luckily you might find what's wrong. Or give up at that point then send it to a transmission specialist. I'd get a rebuilt one, I've been considering it. Trannyman has this website, I wish he wasn't over four hours away from me.Transmissions

Originally Posted by Trannyman95

Your car has a4T65E-HD transmission, the HD meaning Heavy Duty as this is what the supercharged cars came with and isnt much more than a larger differential and torque converter. The rpm drop still sounds pretty typical in 4th gear as the pcm gradually ups TCC duty% to make a full lockup but the two steps that it makes doesnt sound right. Typically what you will feel from a stop is this......
Take off from stop and shift into 2nd, then speed up more and shift into 3rd, then TCC will apply in 3rd gear and release momentarily as it shifts into 4th so you feel the bump into 4th and see the rpm drop, then TCC reapplies once in 4th gear again having a gradual rpm drop. The torque converter clutch is never 100% locked with zero slippage. The pcm wants to maintane a 2-50 rpm slippage at all times for a smooth feel, so when accelerating and TCC applies it will slip at bit before the rpms drop down a good amount and when you give it a bit more throttle the rpms will go up a little then pull back down as the pcm has to compensate for the greater engine load. If you are interested in tech manuals I have info on the ones that I offer here....

http://www.grandprixforums.net/f21/4...edge-8805.html

The GM Hydramatic book explains the fundamentals of the trans and goes no diagnostic info. It is pure information, sort of a the-way-things-work type of book if you will.

The 4T65e is typical transmission. Only select models of GTP's had the HD. What you are experiencing is the shift kit (mechanism) has weakened...easily fixed for about 80 bux online from www.pfyc.com, no big deal. I am dealing with the same deal, only mine (hd) likes to lock up quicker and at lower speeds and with the 325 lb. ft. of torque likes to get me into trouble idling at 40 in city steets...mine locks up too early...
Shift kit, 80 bux, if that doesn't do it, then get the HD tranny, and i have found them cheaper than factory units...