P0741 code only, 04 Deville

[Cadillac Jim]

The TCC, by soft-locking the torque converter, takes power that would be lost in normal torque converter slippage and puts it to the drive wheels. This does two things, improvement of fuel economy and reduction of transmission heating. Power isn't affected because the TCC drops out and you get the torque converter when you press the accelerator.

Looking at the numbers, if you lose 1 mpg at, say, 20 mpg at 60 mph (yes, you will get better gas mileage than that, but bear with me and we will scale things), that means that every hour you will use three gallons, about 5% of which will go into heat in the transmission. Every six hours or so, you will burn a gallon of gas that goes into heating the transmission. That's a lot of heat. You can scale things for 27 mpg and its still a lot of heat.

Yes, the 4T80E with an intact, working transmission cooler and a radiator in good working order will absorb that heat. But if the TCC is working properly only a small fraction of that heat is put through the transmission.

Most people that report going a long time or putting a lot of miles on a transmission that reports a P0741 don't do long road trips. One very highly respected member here, KHE, had a bad TCC disintegrate, effectively totaling his transmission; this may be the exception but it is a proven hazard.

Bruce, our host, ever the consummate gentleman, said it best:

I would address the transmission before a long roadtrip, unless you have very flexible travel plans.

The good news is that if you have HISTORY electrical codes related to the P0741 such as P0740/P0743/P0744/etc. then the problem is likely the TCC solenoid, which can be changed with the transmission in the car. Hard-nosed maintenance freaks like me would change all the solenoids just because they are inexpensive relative to the job of replacing them, and the job of replacing all of them is about the same total hours as replacing one of them. Also, I would replace the solenoids if I changed the torque converter to fix a TCC as part of the process of ensuring a trouble-free transmission.

Another thing you might consider in terms of investing in the car with a transmission repair, whether it be replacing the shift solenoids, replacing the torque converter, or a full rebuild, is that the current GM transmission fluid for your transmission, Dexron VI, offers 240% the transmission life of the OEM fill for the 1993-2004 model years. If you do a transmission flush (the standard transmission service at GM dealers), the remaining life of the clutches will be multiplied by that factor. In addition, cold shifting of the 4T80E improves dramatically with Dexron VI over Dexron III (my personal experience and observation).