[i82much]

I have a 2016 silverado 2500HD with the 6.0 vortec and the 6L90. At 120k miles of very light usage, I am getting a P0700 code and a P0741 code.

Took it to a shop and they say the converter is not locking up. Another issue I noticed is a delayed upshift from third to fourth gear, it happens at a higher RPM than it used to.

It seems most likely me that the 4-5-6 clutch needs to be replaced because the TCC took a dump. Is there any chance at all that just getting the converter to lock up (by replacing the solenoid or converter itself) will cure the 3-4 upshift?

[Half-Inch Stud]

I know nothin about the 6L90 but my opinion is the locking converter doesn't play into the (3-4) shift delay.

4-5 or 5-6 delay could be CPU decision based on valvebody PSI switches used as indicators of HYD circuit status. See here is where i'd say you could drop the pan, h replace the filter and the pan fluid) and drop the switch plate to go and clean the switches of the gray gunk that may prevent good contact.

Did a search; 6L90 common to develop a "3-4 shift flare". Top-off fluid level and hope it's resolved. Some say happens at cold only, and goes away when heated up. Some say either a TCM reflash (solves it) where a rebuild doesn't solve it. And reflash doesn't solve it because a seal (lipseal? Shaft o-ring?) is not sealing to bore for clutchpack.

My opinion is the seals being 10 years old ought be good as new. Look into reflash.

Order of to do:
Top off fluid, drive it.
Drop pan to access switch plate, clean it, change filter, pan fluid. Drive it.
Request TCM reflash.

[ts3189]

Replace the fluid. Worked for me.

[i82much]

I appreciate the feedback. I took it to a local transmission shop with a good reputation. The shop is confident that the converter needs to be replaced because it is not locking up when commanded to do so. Seems to be a pretty common failure mode for this transmission. Based on what they saw in the pan, they think I caught it early enough to maybe get by with just replacing the converter. They are going to look at the pump and clutches to see if they need to go further or not.

When I first took it in they seemed to think a full trans rebuild was most likely but now they seem to think I got lucky. That is a good sign from my perspective, not too often that things get better instead of worse when a repair shop starts digging deeper!

[Formulabruce]

Lock up solenoid, can replace with pan off

[i82much]

Originally Posted by Formulabruce

Lock up solenoid, can replace with pan off

I think they must have tested that. They are replacing the converter and not replacing the TEHCM. It would be pretty obvious if they replaced the converter and not the TEHCM and then it turned out to be a faulty lockup solenoid, no?

[Half-Inch Stud]

Good luck, and good shiftin