TX14-LL3500
Junior Member
I have a stock Laramie Longhorn dually 6.7L I6 turbo diesel mega-cab with 68rfe, 144K miles, that went into limp mode while driving and had it towed to a shop, P0750 was the only failure code. 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 (includes the solenoid), 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 out completely other than P. The only intermittent issue I've experienced since I bought the truck w/34K miles, is the transmission sometimes will not go in Park and I have to move the shifter again before it locks in. While it was still under warranty I reported it multiple times, the dealership would attempt to duplicate the issue but tell me no trouble found.
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.
Could this actually be an ECM failure or something else?
Is there a way to test the VB Assy uninstalled from the truck to ensure it is functioning properly and not a new DOA part?
Is there a more detailed method in testing the wiring, pins, etc. beyond general end-to-end voltage testing between the VB and ECM?
What electronic component on the transmission is communicating to the ECM since the 68RFE does not have a transmission controller like the AISIN does?
Thank you in advance!
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 out completely other than P. The only intermittent issue I've experienced since I bought the truck w/34K miles, is the transmission sometimes will not go in Park and I have to move the shifter again before it locks in. While it was still under warranty I reported it multiple times, the dealership would attempt to duplicate the issue but tell me no trouble found.
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.
Could this actually be an ECM failure or something else?
Is there a way to test the VB Assy uninstalled from the truck to ensure it is functioning properly and not a new DOA part?
Is there a more detailed method in testing the wiring, pins, etc. beyond general end-to-end voltage testing between the VB and ECM?
What electronic component on the transmission is communicating to the ECM since the 68RFE does not have a transmission controller like the AISIN does?
Thank you in advance!
