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Discussion Starter #1 (Edited)
Hi All:

I am seeing some weird stuff after some history with my transmission; trying to figure out where the problem could be, whether the transmission, a solenoid, the TCM, or somewhere else. The car is an '07 CTS base model with 140K miles. My son normally drives it.

About 15 months ago, the car dies, fluids everywhere. Except it is not a normal color; it turns out the radiator broke so that the engine coolant and the transmission fluids were mixing and spewing out. The car was not driven very far like that, talking yards not miles. The excellent repair shop guys replaced the radiator, flushed the engine coolant, and drained the transmission fluid, then put it all back together the way it should be. The car drove just fine for about a year.

Lately, we noticed that the car was shifting funny between 2nd and 3rd. Also got a P0748 code: pressure control solenoid A. A little research, and some review of the paperwork from the repair shop guys, noted a remark: "replace the transmission fluid again some time within a year". So, we replaced the fluids and filter, and the pressure control solenoid, and the 2-3 shift solenoid, and put it back together. WE DID NOTICE a tiny amount of what we call "clutch material" in the pan. Hardly enough to press together to make much more than a small aspirin, not even close to that. At the same time, we had a P0443 Evap Control Circuit so we replaced the purge valve while we had tools around, we were also having trouble before this starting the engine with less than 1/4 tank after not starting for a few days.

Now, two weeks later: some new problems with the transmission, the cruise control and the sport mode won't work like they should, the P0443 did not go away, plus we have a P0621 GEN Lamp L Control Circuit that we had all along that not dealt with yet. We also had some previous codes that went away on their own before all this transmission mess started (C0228 on the ABS and some code I cannot find that had us considering replacing one or both of the catalytic converters and maybe their O2 sensors) and those codes are not back, but in the back of our minds, something triggered those before.

So, more details on the transmission, cruise control, and sport mode:
1) If I do a reset (remove cable from positive battery terminal for 30 minutes or so), everything works right again: 5th gear works like it should, cruise control works like it should, and the sport mode works like it should. Repeats every time I reset things.
2) After about 15 minutes of normal driving, the sport mode is the first to go: the stick shift motion does not shift the transmission gears, it ignores the shift requests
3) About the same time, cruise control is gone, meaning, it won't turn on at all and the green icon on the dash does not light up, the option does not exist to set the speed.
4) Soon after that, the car only goes up normally to 4th gear as you accelerate; no shift to 5th gear happens.
5) In all of this, downshift when accelerating (say stomp on the gas when at 40, you might expect the car to bounce down from 4th to 3rd say) doesn't behave properly at anytime, whether everything else is normal or everything else (5th/cruise/sport) is not normal. And I do a battery reset, and we go back to step 1.

EDIT: Trying to figure out what to do next, after thinking it through, we decided we needed to have the engine running to refill the transmission fluid. This was because we only got almost 6 quarts in. So we got the car up in the air again, kept the car running, and got the 7.4 quarts in there, roughly. So, after we replaced the two solenoids, we had run two weeks about 1.5 quarts low on fluid. The test drive after the top off was fine again for the first 15 minutes, other than the passing gear downshift thing, and then they all went away again. I reset it one more time on Sunday, and so far, it has been fine, being used as a daily driver, 5th gear and cruise and sport mode are all available.

So, we are confused about what to try next, expecting the issue to show up again soon. END EDIT. Is it the TCM? Is it the transmission? Options we are considering:
1) Replace the transmission with a used one with less miles. $400 for the tranny plus a day or two in the barn plus $100 in fluids and new filter and gasket.
2) Try another drain, replace filter and gasket, and refill and replace the 3-4-5 shift solenoid. $70 for the new solenoid, 3 hours in the barn plus $100 in fluids and new filter and gasket.
3) Replace the TCM. Haven't looked up the cost in time and dollars yet, probably a couple of hundred bucks and a few hours in the barn.
4) Should we fix these other codes first, maybe those are messing things up?

If you are still with me here, thanks! If you are in Central Ohio, I will find a way to buy you a cup of coffee!
 

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Once fail codes show up, the cruise control goes off line. If the codes are tranny codes then extra tranny functions are no longer available.
 

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Discussion Starter #3
I added a detail I had forgotten: here it is, I edited the story above as well.

Trying to figure out what to do next, after thinking it through, we decided we needed to have the engine running to refill the transmission fluid. This was because we only got almost 6 quarts in. So we got the car up in the air again, kept the car running, and got the 7.4 quarts in there, roughly. So, after we replaced the two solenoids, we had run two weeks about 1.5 quarts low on fluid. The test drive after the top off was fine again for the first 15 minutes, other than the passing gear downshift thing, and then they all went away again. I reset it one more time on Sunday, and so far, it has been fine, being used as a daily driver, 5th gear and cruise and sport mode are all available.

So, we are confused about what to try next, expecting the issue to show up again soon.
 

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Discussion Starter #4
Just to bring closure here: be sure to have the engine running when you add transmission fluid to get that last quart and a half in there, even for a car like the CTS where the fill plug is beneath the car, meaning no dipstick or fill from the top of the engine. The transmission and the cruise control and the sport mode have all been fine with the transmission filled with the right amount of fluid.
 
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