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Discussion Starter #1
Background:
The vehicle in question is a stock 2009 Chevrolet Impala with the 3.5L engine and 4T65E transaxle. It has around 125,000 miles on it. There is no check engine light, and I haven’t been able to pull any trouble codes with a basic scan tool. The transmission fluid was changed by the dealer about a year and a half ago at 115,000 miles. They did not change the transmission filter or pull the pan. The fluid looked to be in okay condition before it was changed. The transmission fluid, as it should, looks new and doesn’t seem to be frothy or otherwise full of bubbles. It looks to me like it might be slightly overfilled. The problem has been occurring for at least a year; I’m not sure if it coincides with the fluid change.

Complaint:
Occasionally, when I come to a complete stop, then go to take off again, the engine will rev up to 2000ish rpm but the car moves forward with very little power as if the transmission is slipping, but then it will lurch forward, sometimes quite harshly depending on how much gas you’re giving it, then resume normal operation. It’s as if it was taking off from a stop in a high gear then downshifting suddenly to first, but I don’t know if that’s what really is going on. This happens maybe once or twice per hour of driving. Sometimes more, sometimes less. It seems like it tends to happen when the engine/transmission are hotter, but that’s not the case 100% of the time.

Aside from this issue, the engine runs well and the transmission upshifts/downshifts fine and the torque converter seems to lock up and hold fine. When it’s not having trouble, it will launch off the line with plenty of power if you want it to; the transmission does not feel weak.

I’ve read a bit about some problematic EPC solenoids in these transmissions, but I don’t have any way to do further diagnostics on this transmission.

Question:
With that all in mind, does this issue sound familiar? Ultimately, I’ll likely end up bringing it to a transmission shop, but I’d like to be as informed as possible before doing so. My experience with other vehicles is that any transmission shop just wants to do a full $3000 rebuild, but I refuse to believe that is necessary here. It seems like an electrical/sensor/computer issue or a pressure control problem. Unfortunately, it seems that most of the relevant sensors and solenoids are not in the pan and are difficult to access. The intermittent nature of the issue will prove challenging for most transmission shops as well. Any information would be greatly appreciated.
 

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The "flush" will stir up the particles in the trans. Some of the particles are ferrous material which will stick to the magnetic part of the solenoids so they don't operate correctly. Changing the solenoids probably will fix the problem but is labor intensive.
Dropping the pan and changing the filter usually works better.
 

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^+1 with Bill. Has the atf filter ever been changed in 125k mi.? I'd recommend a pan drop fluid/filter change ea. 30k mi.
 

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Discussion Starter #4
To my knowledge, the AT filter has never been changed. When I brought it to the dealer I discussed this with my service writer and he said that it was Chevrolet's policy to only do fluid exchanges and to not open the pan or replace the filter unless specifically requested. Something about not wanting to introduce contaminants into the transmission unnecessarily. Not sure if I believe it, but that's what he said.

As far as the "flush" goes, I'm aware of potential trouble they can cause, particularly for neglected transmissions which have dirty fluid or where the friction material suspended in the fluid is all that's keeping it going. This was a concern of mine so I was sure to confirm with the service writer that they were doing only a "low pressure" fluid exchange, with no special cleaners or chemicals. As it was explained to me, the fluid is slowly pumped out through the filter and out the tranny cooler line while new fluid is added through the other cooler line. The fluid was red prior to the flush, not burnt or dirty, so that factored into my decision to go ahead with the fluid exchange as well.

Do you think it would be useful at this point for me to pull the pan and change the filter? I thought I also read something at some point about a new style of pan magnet that GM called for. If nothing else, I'd be curious to see what kind of shape the filter is in and what there is on the magnet or on the bottom of the pan.
 

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Do you think it would be useful at this point for me to pull the pan and change the filter?
Short answer is yes.

My '08 did the same thing. I replaced the oil pan with the Dorman pan. It has a drain plug so you can change the oil more often. I change it out every-other motor oil change.

I also added the 2nd magnet as recommended by GM along with replacing the filter. It goes without saying, use full synthetic ATF.

I initially drove the vehicle about 100 miles and drained the fluid and re-filled. So-far so good.

If you do this its also a good time to install a shift kit; while your there, why not.
 

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Discussion Starter #6
I've been looking at that pan for awhile, but I have a question. Does the drain plug interfere with the placement of the new donut-shaped magnet that is to be installed? Or is the inner diameter of the magnet such that it fits around the bung for the drain plug? As far as shift kits go, the Transgo 4T65E kit says it works for 1997-2008. Is this accurate?

TransGo 4T65E: SK 4T65E
 

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The 2nd magnet has to be installed next to the drain hole. Unfortunately it doesnt fit around it. The 4T65E kit is the one I used, but mine is an '08. You might want to check with TransGo to make sure it works in the '09. I would think it would, but better safe than sorry.
 

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Discussion Starter #8
I ordered the Dorman pan and the AC Delco pan magents & filter as well as 8 qts of Dexron VI. I am probably going to hold off on a shift kit at this point even though the timing would be convenient since I'll have the pan off. This way, I'm not changing too many variables at once, giving me a better idea of what solves (or doesn't solve) the problem. It'll be some time before I get the new parts on but I'll update with anything interesting I see once I get the pan opened up.

Thanks everyone for all the help.
 
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