Please help. I recently bought a 2016 GC 3.6 with 62TE transmission that has approximately17000 miles. The day after purchasing, after about 50 miles, engine and stability alerts came on. codes P0740 (TCC) and C1252-92 ( ABS vacuum pump)came up. I took it in for diagnosis and found that the codes were just recently erased. I foolishly put too much trust in the dealer and took his word concerning the condition and maintenance of the van. Oil and trans fluid were black and burnt. Trans was overfilled. Other fluids were at min levels. All which were supposedly just serviced. The shop report showed codes p0740, p729, p1790 and p258a stored in system. They recommend replacing transmission, torque converter, trans coolant lines, and oil cooler pump. Their quote was just over $8000. There's no way I can afford that. The dealer has no concern. I'm going to have to try to make the repairs myself. Ive been out of work on short term disability from a crash I was in from July last year. My family has been without a vehicle for 9 months and had to use my moms car.
I've already flushed out the coolant system, changed oil and transmission fluids and filters. The trans fluid was burnt and very dark but no metal or any debris. It was also 3 quarts overfilled. The coolant runs about 200-220°F. I dont know the trans temp but it does take a good while for the fluid to get hot. There doesn't appear to be any substantial fluid leaks, everything seems to look ok. The only codes showing now is p740, c1252-92 about every 60 miles and sometimes p868. The transmission does fine until the engine light comes on, usally with the stability at the same time. The rpms will drop and go back up when applying breaks, sometimes it will shift hard or slip. Once it over revved to 7000 rpms. I can't really make the p740 come up, but seems to come on when hot. The c1252 will come up when I pump the breaks. I really need to know how to trouble shoot this thing and what to look for. I can't afford to throw parts at it and I dont want to have to take anything apart more than once. This is our only vehicle and have to drive daily. Right now im just resting the codes every day untill I can figure out what to do. Thank you so much if you've gotten this far reading. Any suggestions will be most appreciated

 

I'm also here thinking in my old school ways that none of this should be a mystery. Was just sorting through 5th Gen GC posts hoping to find similar issues to mine. Since this post had a generic title, I read through your issues. One thing that is clear: Most posts are completely unanswered, just as yours has been. Oh they get read a lot. Just others in the same boat as you n I searching for answers. I read where you learned your dealer only serves itself with the simple goal of making money. I recently learned the only people able to access the info we need are at the dealer. But, the dealer isn't interested in actually solving problems for customers. They just want to sell parts.
Seems you are ahead of me in understanding some error codes. Could you point me to a list of them?
Rather than take disability, I took early retirement - but my disabilities are verifiable & it takes me forever to accomplish what I once did in minutes.
I'll be sharing what I learn along the way - just a whole different set of problems from yours so far.

As for your transmission fluid, I do have an old school solution for getting all the burnt fluid out. Use a cheap 12V fuel pump to flush the cooler & lines with fresh fluid. You may find that system clogged internally. Perhaps this is also contributing to the higher than expected engine temps you mention.

Praying the best for you.

b

 

You mentioned that stepping on the brakes affects RPM, this makes me think of a vacuum leak. Do a complete check of all vacuum hoses...they simply don't last and given the burnt trans fluid, there may have been high heat which will age the hoses faster

c1252 is a vacuum pump failure
Take a look at this:
https://static.nhtsa.gov/odi/tsbs/20...73320-9999.pdf