2010 TC transmission/torque converter acting erratic

[Matt416]

I have a 2010 TC, basic model, with about 81,000 miles. I changed the ATF 9,000 miles ago. I have not had any transmission issued up until this point. Transmission fluid still looks clean and full. But now this happened:

Thurs 5/12 - early morning on the freeway, torque converter clutch would not lock up in 4th gear, RPM too high for 4th gear going 65 mph (shifting had been 'harsh' on and off for a few days). Orange wrench light came on, OBD2 said pending fault P0741. Went home, found oil in the 9-pin plug that goes into the transaxle. Cleaned out oil and did not find any wire damage. Everything seemed to work fine for a few days, drove roughly 150 miles.

Tues 5/17 - afternoon, now the torque converter clutch was not disengaging, so slowing down to idle the engine would die. Also died in reverse (engine runs and idles perfectly). No error codes found. Cleaned the plug again even though it looked clean, and vehicle idled fine in drive and reverse.

Wed 5/18 - early morning on the freeway, shifted fine but torque converter clutch would not lock up in 4th gear (RPM too high for 4th gear going 65 mph). Tried disengaging and engaging the overdrive button, and the overdrive-off light came on the first few times, but then would not come on again. Got off the freeway and then back on to go home, shifted manually into 1st, 2nd, and then drive (shifting was not very smooth), but the vehicle would not go into 4th (overdrive). Kept trying the overdrive button, the overdrive-off dash light never came on, and eventually the vehicle went into 4th gear but the torque converter clutch was still not engaged.

Took apart the 9-pin connector, put it back together, double-checked all wires, everything looked good. Test drove in the afternoon, started out on the freeway okay, a little rough shifting, overdrive-off light was working, went into 4th and the torque converter clutch locked in for a little while, then disengaged. The wrench light came on. Got off freeway, drove around the neighborhood, motor did not run rough or die at stops with the transmission in drive, and the wrench light went off. Back on the freeway it would not go into 4th for a while, I tried hitting the overdrive button several times, but the overdrive-off light on the dash would not come on. Got off the freeway, drove around the neighborhood, turned engine off then on, now the overdrive-off light was working, got back on the freeway, now it shifted into 4th but clutch still did not lock up.

I am finding this very frustrating. My gut feeling is this is an electrical/computer problem. According to the shop manual (and tracing the wires) there is no transmission module. The PCM controls the transmission entirely. I thought it might be a solenoid in the transmission, but as far as I can tell, there is no specific solenoid in the transmission that controls the torque converter engagement. Any ideas for what to try next would be greatly appreciated!

Thanks in advance,
Matt

[Matt416]

I am still perplexed by how the torque converter clutch is directly controlled. The PCM decides when it should be engaged or disengaged, but I can’t find a specific solenoid, or even an electrical circuit to actually operate the engaging or disengaging of the torque converter clutch. Any ideas?