Limp mode - no codes

[ccmano]

I need some help from the collective brain trust. I'm helping my buddy with his 2018 2500 6 speed auto trans with about 39k miles. It is under extended warranty. It is increasingly lapsing into limp mode (1st and 4th gear only) and showing high trans fluid temps (over 200'). It shows no codes. Initially only while towing but now after normal driving of half an hour or so. He has taken it to the dealer twice. They say they can't duplicate the problem (no surprise) and reprogramed the TCM. Searching the forums, I'm familiar with the valve body problems and the trans thermostat problems, not to mention all the generally defective transmissions. I find the lack of a code odd. I've told him to get the truck into limp mode and drive to dealer, not turn it off, and take a service advisor for a drive. What if anything are we missing here? I suspect the VB. Any input is welcome.
H

 

[Burla]

You loose the overdrive pistons first with that valve body I am guessing 68rfe, could be cross leaks. Get a bypass valve and get the heat out of the transmission, it is a conundrum if you live in the snow but regardless those heat valves fail and when they do they take the transmission with it. Use a pao transmision fluid which lowers the safe operating temp, I use redline c+ works great, there are others as well. Look at pour points on stat sheet stay away from the 49F PP's, this is where upgraded fluids pay for themselves, in the extremes hot and cold, see chart redline line 2 and 5, mopar line 1. See safe operating range of temps. There is a ton of threads on this bypass, it is simple to do and will replace that valve pumping heat into your trans. forum search rfe thermal bypass let me know if you have any q's.

 

[Burla]

Corey aka hemi395 the great researcher on the board found this amoung many other rfe vids online, not saying this brand is the best, just the info is solid. I do believe this video explains the loss of overdrive pistons.

Product Overview: ATS 68RFE Valve Body and ATS Co-Pilot

Clint Cannon, President of ATS, describes the inherent weaknesses of the 68RFE (545RFE, too) valve body. This is a comprehensive overview of the numerous pro...

youtu.be

 

[Burla]

9 minute mark explains fix od cluth vb pistons.

 

[ccmano]

No sooner I posted, it decided to throw a code. Luckily he followed my suggestion to go straight to the dealer. They checked and determined "bad OD". Nothing more specific (I wasn't there). They are replacing the entire transmission under warranty and estimate a ~3 month wait. Looks like you hit it on the head Burla! He's going to trade the truck in on a new one.
I did the thermostat bypass and fluid/filters change on my 14' 2500 66rfe with 83k on the clock last year. So far so good. Although I don't tow in OD. I'm thinking I may change out my valve body for a Sonnax next year prophilactically given the age and mileage on my truck.
H

 

[Burla]

Sounds like your dealer is milking the manu, it's ok though it will be easy to resale with a new tranny and paper work. I would bet it is just the VB, but who cares get a new tranny and sell it.

 

[Gordo2212]

This happened to my 2018 3500 6.4l. Would go into limp mode with no codes while towing my camper. CE light eventually came on though. It was the valve body. Got that changed out under warranty and no problems since.