2014 3500 w/68RFE, P0750... Help Please

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TX14-LL3500

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2014
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Diesel 6.7
I have a Laramie Longhorn dually mega-cab, 144K miles, that went into limp mode while driving. I had it towed to a shop, code pulled was P0750. I am being told all wiring was checked between the ECM and VB, no trouble found. They replaced the valve body w/new VB assembly, this did not resolve the issue, they are unable to communicate with it and are unsuccessful in clearing the P0750 code. Now I am being told the ECM must be bad based on their determination of next steps to resolve the communication issue to the VB.
Truck history: this is the 2nd VB Assy installed on the truck, 1st failed just under 100K, covered by warranty in 2018. When the transmission failed, it went completely out and lost power. I was told plastic pieces of the VB broke off inside the transmission.

Based on information I have read on this forum and YouTube, it appears the 6.7L+68RFE on the 3500s, has a great deal of issues, the valve body fails a lot and I am trying to prevent continuing to throw 1Ks $ at unsuccessful part replacements; these guys are not experienced enough with my particular truck situation. I am hoping someone can provide feedback and assist me. Thank you in advance!
 

mtnrider

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This is a code for shift solenoid A, are they replacing that (with a new one) when they did the valve body??

If you read between the lines you will find the bad reputation is mostly do to people tuning the truck and cranking up the HP (and driving like a teenager). It stock forum it's pretty reliable.

I'd find another transmission shop for starters

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TX14-LL3500

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The Mopar VB Assy includes a new solenoid, I made a point to ask. This the 2nd shop I have taken it to, they are both pointing to the ECM as next steps. (based on the fact the ECM cannot communicate with the VB) The truck is behaving the same with both of the 2 VBs, making them think the ECM is now the problem.
 

GsRAM

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What is the cost of a new ecm? Does a new one need programmed to your truck if replaced? I'd assume that's the case whether new OEM or getting one at a junk yard (what I'd try to do if it was me) I've not read of many ecm failures on these trucks so I'm a bit skeptical of that conclusion at this point.

Yes the OEM valve bodies are known to be problematic, if you replaced OEM with another OEM, I'd not have done that. Sonnnax makes an upgraded replacement valve body I'm considering installing the next time service my trans.

What other diagnostic work has been done so far? This sounds like the same replay again....these modern day techs (kids) have no clue how to diagnose issues and if a laptop can't tell them what's wrong, they are lost.

I hate to even suggest this, but perhaps a trip to a trusted local dealer is in order for even just a few hours of diagnostic time to test the ecm and confirm its status is in order at this point.

Anything is possible, I just have a hard time believing the ecm is bad at this point. How old is the battery in the truck? Has it been load trested recently or replaced ever? I think I'd start there if it still the OEM and even if not it can't hurt. Pull it and take it to your local auto parts store. They will load test it for free. Good luck.
 

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