Well, here we go again.
Last year now I was driving to pick up someone and my car's TC was locking up like it should, however I did notice it was kicking down more often when I was heading up a fairly long uphill grade. I understand it's supposed to depending on load / throttle, etc.
Get to my destination, pick up my passenger, and on the way back, my MIL came on and it would no longer lock up - P07040 - TCC Circuit Open / Shorted.
Fast forward to two months ago and I took it to a local transmission shop who insisted that it was not the solenoid, but the TCM, based on what his scan tool was telling him, the signal for TCC would drop to zero and stay there.

I'm convinced the solenoid finally ate itself. The car had 250K miles when it died. I tried testing coil resistance at Pin 5 at the harness sub connector (The orange/brownish one) and read 33 Ohms. Book says between 5-20 Ohms. I know the TCM is buried in the Console and I really hope I don't have to tear it apart.
What say you, hivemind? I have not dropped the pan yet to observe if the solenoid actually moves.

I appreciate your input.

 

not sure if this will work but it's worth a try, I had a P0720 and it resolved it:


this is a common part that breaks, you can replace it yourself, it's very easy and very cheap.
Once replaced, take the car on a long drive (30 mins or so) above 45mph and see how it behaves (engine and transmission fluid need to be at normal warm temperature first)
out here, it's below freezing now so the TCM will not lock until everything warms up, for me it takes about 10-15 mins of interstate, then it locks and everything is normal.

But 100% for sure if that sensor is faulty, the TCM will never send the signal. Try this first.
I doubt that the TCM is fried, seen too many posts of guys replacing them for nothing, more likely the solenoid, if this does not work.

Have you been regularly draining and refilling the transmission fluid over the years? + filter & magnet clean?

you can always take the solenoids out of the transmission and see if they work (search on youtube)
that would give you a definite answer, but I don't think anyone would be surprised if they are going bad at that mileage.

 

Heya. I already did replace the Revolution Sensor last year. It was failing and throwing that P0720, also causing the transmission to drop out of Overdrive at random while cruising on the freeway. I would have to stop, put it in park to 'reset' it. Once I replaced the sensor, it fixed that issue. I would say maybe 3 or 4 months after is when I lost the TCC circuit. It is definitively a P0740 (TCC Circuit Open / Shorted). I can clear the MIL and it comes back almost right away, even if I turn off Overdrive / keep the speed under 40mph.

I appreciate the suggestion though, thanks.